Publications by authors named "Yitzhak Hadar"

87 Publications

Elevated CO and nitrate levels increase wheat root-associated bacterial abundance and impact rhizosphere microbial community composition and function.

ISME J 2021 Apr 18;15(4):1073-1084. Epub 2020 Nov 18.

Soil, Water and Environmental Sciences, Agricultural Research Organization, Volcani Center, Rishon LeZion, Israel.

Elevated CO stimulates plant growth and affects quantity and composition of root exudates, followed by response of its microbiome. Three scenarios representing nitrate fertilization regimes: limited (30 ppm), moderate (70 ppm) and excess nitrate (100 ppm) were compared under ambient and elevated CO (eCO, 850 ppm) to elucidate their combined effects on root-surface-associated bacterial community abundance, structure and function. Wheat root-surface-associated microbiome structure and function, as well as soil and plant properties, were highly influenced by interactions between CO and nitrate levels. Relative abundance of total bacteria per plant increased at eCO under excess nitrate. Elevated CO significantly influenced the abundance of genes encoding enzymes, transporters and secretion systems. Proteobacteria, the largest taxonomic group in wheat roots (~ 75%), is the most influenced group by eCO under all nitrate levels. Rhizobiales, Burkholderiales and Pseudomonadales are responsible for most of these functional changes. A correlation was observed among the five gene-groups whose abundance was significantly changed (secretion systems, particularly type VI secretion system, biofilm formation, pyruvate, fructose and mannose metabolism). These changes in bacterial abundance and gene functions may be the result of alteration in root exudation at eCO, leading to changes in bacteria colonization patterns and influencing their fitness and proliferation.
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http://dx.doi.org/10.1038/s41396-020-00831-8DOI Listing
April 2021

Correction to: The microbiome as a biosensor: functional profiles elucidate hidden stress in hosts.

Microbiome 2020 Jun 30;8(1):101. Epub 2020 Jun 30.

Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization-Volcani Center, 7528809, Rishon Lezion, Israel.

An amendment to this paper has been published and can be accessed via the original article.
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http://dx.doi.org/10.1186/s40168-020-00883-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7325669PMC
June 2020

The microbiome as a biosensor: functional profiles elucidate hidden stress in hosts.

Microbiome 2020 05 21;8(1):71. Epub 2020 May 21.

Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization-Volcani Center, 7528809, Rishon Lezion, Israel.

Background: Microbial communities are highly responsive to environmental cues, and both their structure and activity can be altered in response to changing conditions. We hypothesized that host-associated microbial communities, particularly those colonizing host surfaces, can serve as in situ sensors to reveal environmental conditions experienced by both microorganisms and the host. For a proof-of-concept, we studied a model plant-soil system and employed a non-deterministic gene-centric approach. A holistic analysis was performed using plants of two species and irrigation with water of low quality to induce host stress. Our analyses examined the genetic potential (DNA) and gene expression patterns (RNA) of plant-associated microbial communities, as well as transcriptional profiling of host plants.

Results: Transcriptional analysis of plants irrigated with treated wastewater revealed significant enrichment of general stress-associated root transcripts relative to plants irrigated with fresh water. Metagenomic analysis of root-associated microbial communities in treated wastewater-irrigated plants, however, revealed enrichment of more specific stress-associated genes relating to high levels of salt, high pH and lower levels of oxygen. Meta-analysis of these differentially abundant genes obtained from other metagenome studies, provided evidence of the link between environmental factors such as pH and oxygen and these genes. Analysis of microbial transcriptional response demonstrated that enriched gene content was actively expressed, which implies contemporary response to elevated levels of pH and salt.

Conclusions: We demonstrate here that microbial profiling can elucidate stress signals that cannot be observed even through interrogation of host transcriptome, leading to an alternate mechanism for evaluating in situ conditions experienced by host organisms. This study is a proof-of-concept for the use of microbial communities as microsensors, with great potential for interrogation of a wide range of host systems. Video Abstract.
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http://dx.doi.org/10.1186/s40168-020-00850-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7243336PMC
May 2020

Growing a circular economy with fungal biotechnology: a white paper.

Fungal Biol Biotechnol 2020 2;7. Epub 2020 Apr 2.

22Department of Biology, Microbiology, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.

Fungi have the ability to transform organic materials into a rich and diverse set of useful products and provide distinct opportunities for tackling the urgent challenges before all humans. Fungal biotechnology can advance the transition from our petroleum-based economy into a bio-based circular economy and has the ability to sustainably produce resilient sources of food, feed, chemicals, fuels, textiles, and materials for construction, automotive and transportation industries, for furniture and beyond. Fungal biotechnology offers solutions for securing, stabilizing and enhancing the food supply for a growing human population, while simultaneously lowering greenhouse gas emissions. Fungal biotechnology has, thus, the potential to make a significant contribution to climate change mitigation and meeting the United Nation's sustainable development goals through the rational improvement of new and established fungal cell factories. The White Paper presented here is the result of the 2nd Think Tank meeting held by the EUROFUNG consortium in Berlin in October 2019. This paper highlights discussions on current opportunities and research challenges in fungal biotechnology and aims to inform scientists, educators, the general public, industrial stakeholders and policymakers about the current fungal biotech revolution.
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http://dx.doi.org/10.1186/s40694-020-00095-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7140391PMC
April 2020

Seeking the Roles for Fungal Small-Secreted Proteins in Affecting Saprophytic Lifestyles.

Front Microbiol 2020 24;11:455. Epub 2020 Mar 24.

Department of Plant Pathology and Microbiology, The R.H. Smith Faculty Agriculture, Food and Environment, The Hebrew University of Jerusalem, Jerusalem, Israel.

Small secreted proteins (SSPs) comprise 40-60% of the total fungal secretome and are present in fungi of all phylogenetic groups, representing the entire spectrum of lifestyles. They are characteristically shorter than 300 amino acids in length and have a signal peptide. The majority of SSPs are coded by orphan genes, which lack known domains or similarities to known protein sequences. Effectors are a group of SSPs that have been investigated extensively in fungi that interact with living hosts, either pathogens or mutualistic systems. They are involved in suppressing the host defense response and altering its physiology. Here, we aim to delineate some of the potential roles of SSPs in saprotrophic fungi, that have been bioinformatically predicted as effectors, and termed in this mini-review as "effector-like" proteins. The effector-like Ssp1 from the white-rot fungus is presented as a case study, and its potential role in regulating the ligninolytic system, secondary metabolism, development, and fruiting body initiation are discussed. We propose that deciphering the nature of effector-like SSPs will contribute to our understanding of development and communication in saprophytic fungi, as well as help, to elucidate the origin, regulation, and mechanisms of fungal-host, fungal-fungal, and fungal-bacterial interactions.
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http://dx.doi.org/10.3389/fmicb.2020.00455DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7105643PMC
March 2020

Immunomodulating Effects Exerted by Glucans Extracted from the King Oyster Culinary-Medicinal Mushroom Pleurotus eryngii (Agaricomycetes) Grown in Substrates Containing Various Concentrations of Olive Mill Waste.

Int J Med Mushrooms 2019 ;21(8):765-781

Institute of Biochemistry, School of Nutritional Sciences, Food Science and Nutrition, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel.

We have recently demonstrated that we could enhance glucan content in Pleurotus eryngii following cultivation of the mushrooms on a substrate containing different concentrations of olive mill solid waste (OMSW). These changes are directly related to the content of OMSW in the growing substrate. Using dextran sulfate sodium (DSS)-in-flammatory bowel disease (IBD) mice model, we measured the colonic inflammatory response to the different glucan preparations. We found that the histology damaging score (HDS) resulting from DSS treatment reach a value of 11.8 ± 2.3 were efficiently downregulated by treatment with the fungal extracted glucans. Glucans extracted from stalks cultivated at 20% OMSW downregulated to a HDS value of 6.4 ± 0.5 whereas those cultivated at 80% OMSW showed the strongest effects (5.5 ± 0.6). Similar downregulatory effects were obtained for expression of various intestinal cytokines. All tested glucans were equally effective in regulating the number of CD14/CD16 monocytes from 18.2 ± 2.7% for DSS to 6.4 ± 2.0 for DSS + glucans extracted from stalks cultivated at 50% OMSW. We tested the effect of glucans on lipopolysaccharide-induced production of TNF-α, which demonstrated that stalk-derived glucans were more effective than caps-derived glucans. Isolated glucans competed with anti-Dectin-1 and anti-CR3 antibodies, indicating that they contain β-glucans recognized by these receptors. In conclusion, the most effective glucans in ameliorating IBD-associated symptoms induced by DSS treatment in mice were glucan extracts prepared from the stalk of P. eryngii grown at higher concentrations of OMSW. We conclude that these stress-induced growing conditions may be helpful in selecting more effective glucans derived from edible mushrooms.
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http://dx.doi.org/10.1615/IntJMedMushrooms.2019031549DOI Listing
March 2020

Directed Evolution of β-Glucosidase A Towards Enhanced Thermostability.

Int J Mol Sci 2019 Sep 23;20(19). Epub 2019 Sep 23.

Department of Biomolecular Sciences, The Weizmann Institute of Science, Rehovot 7610001, Israel.

β-Glucosidases are key enzymes in the process of cellulose utilization. It is the last enzyme in the cellulose hydrolysis chain, which converts cellobiose to glucose. Since cellobiose is known to have a feedback inhibitory effect on a variety of cellulases, β-glucosidase can prevent this inhibition by hydrolyzing cellobiose to non-inhibitory glucose. While the optimal temperature of the cellulosome is 70 °C, β-glucosidase A is almost inactive at such high temperatures. Thus, in the current study, a random mutagenesis directed evolutionary approach was conducted to produce a thermostable mutant with K and K, similar to those of the wild-type enzyme. The resultant mutant contained two mutations, A17S and K268N, but only the former was found to affect thermostability, whereby the inflection temperature (T) was increased by 6.4 °C. A17 is located near the central cavity of the native enzyme. Interestingly, multiple alignments revealed that position 17 is relatively conserved, whereby alanine is replaced only by serine. Upon the addition of the thermostable mutant to the secretome for subsequent hydrolysis of microcrystalline cellulose at 70 °C, a higher soluble glucose yield (243%) was obtained compared to the activity of the secretome supplemented with the wild-type enzyme.
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http://dx.doi.org/10.3390/ijms20194701DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6801902PMC
September 2019

Identification and manipulation of genes involved in sensitivity to furfural.

Biotechnol Biofuels 2019 4;12:210. Epub 2019 Sep 4.

1Department of Plant Pathology and Microbiology, The R.H. Smith Faculty Agriculture, Food and Environment, The Hebrew University of Jerusalem, 7600001 Rehovot, Israel.

Background: Biofuels derived from lignocellulosic biomass are a viable alternative to fossil fuels required for transportation. Following plant biomass pretreatment, the furan derivative furfural is present at concentrations which are inhibitory to yeasts. Detoxification of furfural is thus important for efficient fermentation. Here, we searched for new genetic attributes in the fungus that may be linked to furfural tolerance. The fact that furfural is involved in the natural process of sexual spore germination of and that this fungus is highly amenable to genetic manipulations makes it a rational candidate for this study.

Results: Both hypothesis-based and unbiased (random promotor mutagenesis) approaches were performed to identify genes associated with the response to furfural. Changes in the transcriptional profile following exposure to furfural revealed that the affected processes were, overall, similar to those observed in . was more tolerant (by ~ 30%) to furfural when carboxymethyl cellulose was the main carbon source as opposed to sucrose, indicative of a link between carbohydrate metabolism and furfural tolerance. We also observed increased tolerance in a Δ- mutant (CRE-1 is a key transcription factor that regulates the ability of fungi to utilize non-preferred carbon sources). In addition, analysis of aldehyde dehydrogenase mutants showed that - (NCU00378) was involved in tolerance to furfural as well as the predicted membrane transporter NCU05580 (-), a homolog of in . Further to the rational screening, an unbiased approach revealed additional genes whose inactivation conferred increased tolerance to furfural: (i) NCU02488, which affected the abundance of the non-anchored cell wall protein NCW-1 (NCU05137), and (ii) the zinc finger protein NCU01407.

Conclusions: We identified attributes in associated with tolerance or degradation of furfural, using complementary research approaches. The manipulation of the genes involved in furan sensitivity can provide a means for improving the production of biofuel producing strains. Similar research approaches can be utilized in and other filamentous fungi to identify additional attributes relevant to other furans or toxic chemicals.
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http://dx.doi.org/10.1186/s13068-019-1550-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6724289PMC
September 2019

Altering NO emissions by manipulating wheat root bacterial community.

Sci Rep 2019 05 20;9(1):7613. Epub 2019 May 20.

Soil, Water and Environmental Sciences, Agricultural Research Organization, Volcani Center, Rishon LeZion, Israel.

Nitrous oxide (NO) is a greenhouse gas and a potent ozone-depleting substance in the stratosphere. Agricultural soils are one of the main global sources of NO emissions, particularly from cereal fields due to their high areal coverage. The aim of this study was to isolate NO-reducing bacteria able to mitigate NO emissions from the soil after inoculation. We isolated several bacteria from wheat roots that were capable of NO reduction in vitro and studied their genetic potential and activity under different environmental conditions. Three of these isolates- all carrying the nitrous oxide reductase-encoding clade I nosZ, able to reduce NO in vitro, and efficient colonizers of wheat roots- presented different NO-reduction strategies when growing in the root zone, possibly due to the different conditions in situ and their metabolic preferences. Each isolate seemed to prefer to operate at different altered oxygen levels. Isolate AU243 (related to Agrobacterium/Rhizobium) could reduce both nitrate and NO and operated better at lower oxygen levels. Isolate AU14 (related to Alcaligenes faecalis), lacking nitrate reductases, operated better under less anoxic conditions. Isolate NT128 (related to Pseudomonas stutzeri) caused slightly increased NO emissions under both anoxic and ambient conditions. These results therefore emphasize the importance of a deep understanding of soil-plant-microbe interactions when environmental application is being considered.
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http://dx.doi.org/10.1038/s41598-019-44124-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6527579PMC
May 2019

Manipulating the Expression of Small Secreted Protein 1 (Ssp1) Alters Patterns of Development and Metabolism in the White-Rot Fungus .

Appl Environ Microbiol 2019 08 18;85(15). Epub 2019 Jul 18.

Department of Plant Pathology and Microbiology, R. H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel

The function of small secreted proteins (SSPs) in saprotrophic fungi is, for the most part, unknown. The white-rot mushroom produces considerable amounts of SSPs at the onset of secondary metabolism, during colony development, and in response to chemical compounds such as 5-hydroxymethylfurfural and aryl alcohols. Genetic manipulation of Ssp1, by knockdown (KD) or overexpression (OE), indicated that they are, in fact, involved in the regulation of the ligninolytic system. To elucidate their potential involvement in fungal development, quantitative secretome analysis was performed during the trophophase and the idiophase and at a transition point between the two growth phases. The mutations conferred a time shift in the secretion and expression patterns: OE preceded the entrance to idiophase and secondary metabolism, while KD was delayed. This was also correlated with expression patterns of selected genes. The KD colony aged at a slower pace, accompanied by a slower decline in biomass over time. In contrast, the OE strain exhibited severe lysis and aging of the colony at the same time point. These phenomena were accompanied by variations in yellow pigment production, characteristic of entrance of the wild type into idiophase. The pigment was produced earlier and in a larger amount in the OE strain and was absent from the KD strain. Furthermore, the dikaryon harboring OE exhibited a delay in the initiation of fruiting body formation as well as earlier aging. We propose that Ssp1 might function as a part of the fungal communication network and regulate the pattern of fungal development and metabolism in Small secreted proteins (SSPs) are common in fungal saprotrophs, but their roles remain elusive. As such, they comprise part of a gene pool which may be involved in governing fungal lifestyles not limited to symbiosis and pathogenicity, in which they are commonly referred to as "effectors." We propose that Ssp1 in the white-rot fungus regulates the transition from primary to secondary metabolism, development, aging, and fruiting body initiation. Our observations uncover a novel regulatory role of effector-like SSPs in a saprotroph, suggesting that they may act in fungal communication as well as in response to environmental cues. The presence of Ssp1 homologues in other fungal species supports a common potential role in environmental sensing and fungal development.
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http://dx.doi.org/10.1128/AEM.00761-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6643241PMC
August 2019

Transformation of lamotrigine by white-rot fungus Pleurotus ostreatus.

Environ Pollut 2019 Jul 12;250:546-553. Epub 2019 Apr 12.

Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, 7610001, Israel. Electronic address:

One of the most persistent pharmaceutical compounds commonly found in treated wastewater is lamotrigine (LTG). It has also been detected in soils and crops irrigated with treated wastewater. Here we focused on the ability of the white-rot edible mushroom Pleurotus ostreatus to remove and transform LTG in liquid cultures. At concentrations of environmental relevance (1 and 10 μg L) LTG was almost completely removed from the culture medium within 20 days. To elucidate the mechanism of LTG removal and transformation, we applied a physiological-based approach using inhibitors and a competing agent. These experiments were conducted at a higher concentration for metabolites detection. Based on identification of sulfur-containing metabolites and LTG N2-oxide and the effect of specific inhibitors, cytochrome P450 oxidation is suggested as one of the reaction mechanisms leading to LTG transformation. The variety and number of transformation products (i.e., conjugates) found in the current study were larger than reported in mammals. Moreover, known conjugates with glucuronide, glutathione, or cysteine/glycine, were not found in our system. Since the majority of the identified transformation products were conjugates of LTG, this study highlights the persistence of LTG as an organic pollutant in ecosystems exposed to wastewater.
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http://dx.doi.org/10.1016/j.envpol.2019.04.057DOI Listing
July 2019

Host Specificity and Spatial Distribution Preference of Three Isolates.

Front Microbiol 2018 10;9:3263. Epub 2019 Jan 10.

Department of Soil, Water, and Environmental Sciences, Agricultural Research Organization-Volcani Center, Rishon LeZion, Israel.

Plant hosts recruit and maintain a distinct root-associated microbiota based on host and bacterium traits. However, past studies disregarded microbial strain-host specificity and spatial micro-heterogeneity of the root compartment. Using genetic manipulation, confocal laser scanning microscopy, real-time quantitative PCR, and genome sequencing we characterized the colonization patterns of three spp. isolates native to wheat roots, on the micro-scale. Namely, isolates NT0133, NT124, and NT128. All three isolates preferentially colonized wheat over cucumber roots that served as control for host specificity. Furthermore, not only had the isolates strong host specificity but each isolate had a distinct spatial distribution on the root, all within a few millimeters. Isolate -NT0124 preferentially colonized root tips, whereas NT0133 showed a preference for zones distant from the tip. In contrast, isolate -NT0128 had no preference for a specific niche on the root. While all isolates maintained genetic potential for motility and biofilm formation their phenotype varied significantly and corresponded to their niche preference. These results demonstrate the importance of spatial colonization patterns, governed by both niche and bacterial characteristics which will have great importance in future attempts to manipulate the plant microbiome by constructing synthetic microbial consortia.
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http://dx.doi.org/10.3389/fmicb.2018.03263DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6335278PMC
January 2019

Root microbiome response to treated wastewater irrigation.

Sci Total Environ 2019 Mar 20;655:899-907. Epub 2018 Nov 20.

Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization - Volcani Center, Rishon Lezion 7528809, Israel. Electronic address:

With increasing fresh water (FW) scarcity, the use of treated wastewater (TWW) for crop irrigation is expanding globally. Besides clear benefits, some undesired long-term effects of irrigation with this low quality water on plant performance have been reported. As the rhizosphere microbiome can mediate plant-soil interactions, an examination of the response of these organisms to TWW is necessary to understand the full effects of water quality. In the current study, the effects of irrigation water quality on the microbial community structure of soil and roots as well as edaphic properties and plant performance were evaluated. We compared soil and roots microbiomes of two different plant species (tomato and lettuce), each grown in two distinct soils, and irrigated with either FW or TWW. Irrigation with TWW significantly increase soil pH, EC, K, Na and DOC, and decrease plant fruit and shoot weight, relatively to samples irrigated with FW. We calculated the effect size of plant species, soil type, and irrigation water quality on microbial community structure in soil and root. In the roots, plant species and irrigation water were the dominant factors in shaping both total (DNA based) and active (RNA based) microbial communities, with both factors contributing similarly to the observed microbial population. Soil type and irrigation water were the dominant factors shaping the total microbial community in the soil and were of similar magnitude. Irrigation water quality is demonstrated to be a major force in shaping root-associated microbiome, leading to altered microbial community structure in the critical juncture between plant and soil.
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http://dx.doi.org/10.1016/j.scitotenv.2018.11.251DOI Listing
March 2019

Spatial Distribution of Glucan Type and Content between Caps and Stalks in : Impact on the Anti-inflammatory Functionality.

Int J Mol Sci 2018 Oct 28;19(11). Epub 2018 Oct 28.

Institute of Biochemistry, School of Nutritional Sciences, Food Science and Nutrition, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel.

is recognized for its prominent nutritional and medicinal value. In our study, we tested the effect of glucans on lipopolysaccharide (LPS)-induced production of TNF-α. We demonstrated that glucan extracts are more effective than mill mushroom preparations. Additionally, the effectiveness of stalk-derived glucans were slightly more pronounced than of caps. Cap and stalk glucans from mill or isolated glucan competed dose-dependently with anti-Dectin-and anti-CR-3 antibodies, indicating that they contain β-glucans recognized by these receptors. Using the dextran sulfate sodium (DSS)-inflammatory bowel disease mice model, intestinal inflammatory response to the mill preparations was measured and compared to extracted glucan fractions from caps and stalks. We found that mill and glucan extracts were very effective in downregulating IFN-γ and MIP-2 levels and that stalk-derived preparations were more effective than from caps. The tested glucans were equally effective in regulating the number of CD14/CD16 monocytes and upregulating the levels of fecal-released IgA to almost normal levels. In conclusion, the most effective glucans in ameliorating some IBD-inflammatory associated symptoms induced by DSS treatment in mice were glucan extracts prepared from the stalk of . These spatial distinctions may be helpful in selecting more effective specific anti-inflammatory mushrooms-derived glucans.
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http://dx.doi.org/10.3390/ijms19113371DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6274982PMC
October 2018

Effects of modification in the white-rot fungus altering substrate preference during biological pretreatment.

Biotechnol Biofuels 2018 27;11:212. Epub 2018 Jul 27.

1Department of Plant Pathology and Microbiology, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, 76100 Israel.

Background: During the process of bioethanol production, cellulose is hydrolyzed into its monomeric soluble units. For efficient hydrolysis, a chemical and/or mechanical pretreatment step is required. Such pretreatment is designed to increase enzymatic digestibility of the cellulose chains inter alia by de-crystallization of the cellulose chains and by removing barriers, such as lignin from the plant cell wall. Biological pretreatment, in which lignin is decomposed or modified by white-rot fungi, has also been considered. One disadvantage in biological pretreatment, however, is the consumption of the cellulose by the fungus. Thus, fungal species that attack lignin with only minimal cellulose loss are advantageous. The secretomes of white-rot fungi contain carbohydrate-active enzymes (CAZymes) including lignin-modifying enzymes. Thus, modification of secretome composition can alter the ratio of lignin/cellulose degradation.

Results: was genetically modified to either overexpress or eliminate (by gene replacement) the transcriptional regulator CRE1, known to act as a repressor in the process of carbon catabolite repression. The -overexpressing transformant demonstrated lower secreted cellulolytic activity and slightly increased selectivity (based on the chemical composition of pretreated wheat straw), whereas the knockout transformant demonstrated increased cellulolytic activity and significantly reduced residual cellulose, thereby displaying lower selectivity. Pretreatment of wheat straw using the wild-type PC9 resulted in 2.8-fold higher yields of soluble sugar compared to untreated wheat straw. The overexpression transformant showed similar yields (2.6-fold), but the knockout transformant exhibited lower yields (1.2-fold) of soluble sugar. Based on proteomic secretome analysis, production of numerous CAZymes was affected by modification of the expression level of .

Conclusions: The gene functions as a regulator for expression of fungal CAZymes active against plant cell wall lignocelluloses, hence altering the substrate preference of the fungi tested. While the knockout resulted in a less efficient biological pretreatment, i.e., less saccharification of the treated biomass, the converse manipulation of (overexpression) failed to improve efficiency. Despite the inverse nature of the two genetic alterations, the expected "mirror image" (i.e., opposite regulatory response) was not observed, indicating that the secretion level of CAZymes, was not exclusively dependent on CRE1 activity.
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http://dx.doi.org/10.1186/s13068-018-1209-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6062969PMC
July 2018

Author Correction: A role for small secreted proteins (SSPs) in a saprophytic fungal lifestyle: Ligninolytic enzyme regulation in Pleurotus ostreatus.

Sci Rep 2018 Mar 6;8(1):4213. Epub 2018 Mar 6.

The R.H. Smith Faculty Agriculture, Food and Environment, The Hebrew University of Jerusalem, Department of Plant Pathology and Microbiology, Rehovot, 76100, Israel.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.
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http://dx.doi.org/10.1038/s41598-018-21904-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5840412PMC
March 2018

Quality of Irrigation Water Affects Soil Functionality and Bacterial Community Stability in Response to Heat Disturbance.

Appl Environ Microbiol 2018 02 31;84(4). Epub 2018 Jan 31.

Department of Soil, Water, and Environmental Sciences, Agricultural Research Organization, Volcani Center, Beit Dagan, Israel

Anthropogenic activities alter the structure and function of a bacterial community. Furthermore, bacterial communities structured by the conditions the anthropogenic activities present may consequently reduce their stability in response to an unpredicted acute disturbance. The present mesocosm-scale study exposed soil bacterial communities to different irrigation water types, including freshwater, fertilized freshwater, treated wastewater, and artificial wastewater, and evaluated their response to a disturbance caused by heat. These effectors may be considered deterministic and stochastic forces common in agricultural operations of arid and semiarid regions. Bacterial communities under conditions of high mineral and organic carbon availability (artificial wastewater) differed from the native bacterial community and showed a proteobacterial dominance. These bacterial communities had a lower resistance to the heat treatment disturbance than soils under conditions of low resource availability (high-quality treated wastewater or freshwater). The latter soil bacterial communities showed a higher abundance of operational taxonomic units (OTUs) classified as These results were elucidated by soil under conditions of high resource availability, which lost higher degrees of functional potential and had a greater bacterial community composition change. However, the functional resilience, after the disturbance ended, was higher under a condition of high resource availability despite the bacterial community composition shift and the decrease in species richness. The functional resilience was directly connected to the high growth rates of certain and proteobacterial groups. A high stability was found in samples that supported the coexistence of both resistant OTUs and fast-growing OTUs. This report presents the results of a study employing a hypothesis-based experimental approach to reveal the forces involved in determining the stability of a soil bacterial community to disturbance. The resultant postdisturbance bacterial community composition dynamics and functionality were analyzed. The paper demonstrates the relatedness of community structure and stability under cultivation conditions prevalent in an arid area under irrigation with water of different qualities. The use of common agricultural practices to demonstrate these features has not been described before. The combination of a fundamental theoretical issue in ecology with common and concerning disturbances caused by agricultural practice makes this study unique. Furthermore, the results of the present study have applicable importance regarding soil conservation, as it enables a better characterization and monitoring of stressed soil bacterial communities and possible intervention to reduce the stress. It will also be of valued interest in coming years, as fresh water scarcity and the use of alternative water sources are expected to rise globally.
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http://dx.doi.org/10.1128/AEM.02087-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5795067PMC
February 2018

A role for small secreted proteins (SSPs) in a saprophytic fungal lifestyle: Ligninolytic enzyme regulation in Pleurotus ostreatus.

Sci Rep 2017 11 6;7(1):14553. Epub 2017 Nov 6.

The R.H. Smith Faculty Agriculture, Food and Environment, The Hebrew University of Jerusalem, Department of Plant Pathology and Microbiology, Rehovot, 76100, Israel.

Small secreted proteins (SSPs), along with lignocellulose degrading enzymes, are integral components of the secretome of Pleurotus ostreatus, a white rot fungus. In this study, we identified 3 genes (ssp1, 2 and 3) encoding proteins that are annotated as SSPs and that exhibited of ~4,500- fold expression, 24 hr following exposure to the toxic compound 5-hydroxymethylfurfural (HMF). Homologues to genes encoding these SSPs are present in the genomes of other basidiomycete fungi, however the role of SSPs is not yet understood. SSPs, aryl-alcohol oxidases (AAO) and the intracellular aryl-alcohol dehydrogenases (AAD) were also produced after exposure to other aryl-alcohols, known substrates and inducers of AAOs, and during idiophase (after the onset of secondary metabolism). A knockdown strain of ssp1 exhibited reduced production of AAO-and AAD-encoding genes after HMF exposure. Conversely, a strain overexpressing ssp1 exhibited elevated expression of genes encoding AAOs and ADD, resulting in a 3-fold increase in enzymatic activity of AAOs, as well as increased expression and protein abundance of versatile peroxidase 1, which directly degrades lignin. We propose that in addition to symbionts and pathogens, SSPs also have roles in saprophytes and function in P. ostreatus as components of the ligninolytic system.
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http://dx.doi.org/10.1038/s41598-017-15112-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5674062PMC
November 2017

How does cellulosome composition influence deconstruction of lignocellulosic substrates in () DSM 1313?

Biotechnol Biofuels 2017 18;10:222. Epub 2017 Sep 18.

Department of Biomolecular Sciences, The Weizmann Institute of Science, 76100 Rehovot, Israel.

Background: Bioethanol production processes involve enzymatic hydrolysis of pretreated lignocellulosic biomass into fermentable sugars. Due to the relatively high cost of enzyme production, the development of potent and cost-effective cellulolytic cocktails is critical for increasing the cost-effectiveness of bioethanol production. In this context, the multi-protein cellulolytic complex of () the cellulosome, was studied here. is known to assemble cellulosomes of various subunit (enzyme) compositions, in response to the available carbon source. In the current study, different carbon sources were used, and their influence on both cellulosomal composition and the resultant activity was investigated.

Results: Glucose, cellobiose, microcrystalline cellulose, alkaline-pretreated switchgrass, alkaline-pretreated corn stover, and dilute acid-pretreated corn stover were used as sole carbon sources in the growth media of strain DSM 1313. The purified cellulosomes were compared for their activity on selected cellulosic substrates. Interestingly, cellulosomes derived from cells grown on lignocellulosic biomass showed no advantage in hydrolyzing the original carbon source used for their production. Instead, microcrystalline cellulose- and glucose-derived cellulosomes were equal or superior in their capacity to deconstruct lignocellulosic biomass. Mass spectrometry analysis revealed differential composition of catalytic and structural subunits (scaffoldins) in the different cellulosome samples. The most abundant catalytic subunits in all cellulosome types include Cel48S, Cel9K, Cel9Q, Cel9R, and Cel5G. Microcrystalline cellulose- and glucose-derived cellulosome samples showed higher endoglucanase-to-exoglucanase ratios and higher catalytic subunit-per-scaffoldin ratios compared to lignocellulose-derived cellulosome types.

Conclusion: The results reported here highlight the finding that cellulosomes derived from cells grown on glucose and microcrystalline cellulose are more efficient in their action on cellulosic substrates than other cellulosome preparations. These results should be considered in the future development of -based cellulolytic cocktails, designer cellulosomes, or engineering of improved strains for deconstruction of lignocellulosic biomass.
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http://dx.doi.org/10.1186/s13068-017-0909-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5604425PMC
September 2017

Olive Mill Waste Enhances α-Glucan Content in the Edible Mushroom Pleurotus eryngii.

Int J Mol Sci 2017 Jul 18;18(7). Epub 2017 Jul 18.

Edible Mushrooms Development, MIGAL, Kiryat Shmona 11016, Israel.

Mushroom polysaccharides are edible polymers that have numerous reported biological functions; the most common effects are attributed to β-glucans. In recent years, it became apparent that the less abundant α-glucans also possess potent effects in various health conditions. Here we explore several species for their total, β and α-glucan content. was found to have the highest total glucan concentrations and the highest α-glucans proportion. We also found that the stalks (stipe) of the fruit body contained higher glucan content then the caps (pileus). Since mushrooms respond markedly to changes in environmental and growth conditions, we developed cultivation methods aiming to increase the levels of α and β-glucans. Using olive mill solid waste (OMSW) from three-phase olive mills in the cultivation substrate. We were able to enrich the levels mainly of α-glucans. Maximal total glucan concentrations were enhanced up to twice when the growth substrate contained 80% of OMSW compared to no OMSW. Taking together this study demonstrate that can serve as a potential rich source of glucans for nutritional and medicinal applications and that glucan content in mushroom fruiting bodies can be further enriched by applying OMSW into the cultivation substrate.
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http://dx.doi.org/10.3390/ijms18071564DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5536052PMC
July 2017

Ferrichrome Has Found Its Match: Biomimetic Analogues with Diversified Activity Map Discrete Microbial Targets.

Chemistry 2017 Sep 31;23(53):13181-13191. Epub 2017 Aug 31.

Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot, 7610001, Israel.

Siderophores provide an established platform for studying molecular recognition principles in biological systems. Herein, the preparation of ferrichrome (FC) biomimetic analogues varying in length and polarity of the amino acid chain separating between the tripodal scaffold and the pendent Fe chelating hydroxamic acid groups was reported. Spectroscopic and potentiometric titrations determined their iron affinity to be within the range of efficient chelators. Microbial growth promotion and iron uptake studies were conducted on E. coli, P. putida and U. maydis. A wide range of siderophore activity was observed in the current series: from a rare case of a species-specific growth promotor in P. putida to an analogue matching FC in cross-phylum activity and uptake pathway. A fluorescent conjugate of the broad-range analogue visualized siderophore destination in bacteria (periplasmic space) vs. fungi (cytosol) mapping new therapeutic targets. Quantum dots (QDs) decorated with the most potent FC analogue provided a tool for immobilization of FC-recognizing bacteria. Bacterial clusters formed around QDs may provide a platform for their selection and concentration.
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http://dx.doi.org/10.1002/chem.201702647DOI Listing
September 2017

Recombinant ostreolysin induces brown fat-like phenotype in HIB-1B cells.

Mol Nutr Food Res 2017 09 9;61(9). Epub 2017 Jun 9.

School of Nutritional Sciences, Institute of Biochemistry, Food Science and Nutrition, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.

Scope: Brown adipose tissue (BAT) is the main regulator of thermogenesis by increasing energy expenditure through the uncoupling of oxidative metabolism from ATP synthesis. There is a growing body of evidence for BAT being the key responsible organ in combating obesity and its related disorders. Herein we propose the fungal protein ostreolysin (Oly), which has been previously shown to bind to cholesterol-enriched raft-like membrane domains (lipid rafts) of mammalian cells, as a suitable candidate for interaction with brown preadipocytes. The aim of the present study was therefore to characterize the mechanism by which a recombinant version of ostreolysin (rOly) induces brown adipocyte differentiation.

Methods And Results: Primary isolated brown preadipocytes or HIB-1B brown preadipocyte cells were treated with rOly and the effects on morphology, lipid accumulation, respiration rate, and associated gene and protein expression were measured. rOly upregulated mRNA and protein levels of factors related to brown adipocyte differentiation, induced lipid droplet formation, and increased cellular respiration rate due to expression of uncoupling protein 1. rOly also upregulated β-tubulin expression, and therefore microtubules might be involved in its mechanism of action.

Conclusion: rOly promotes brown adipocyte differentiation, suggesting a new mechanism for rOly's contribution to the battle against obesity.
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http://dx.doi.org/10.1002/mnfr.201700057DOI Listing
September 2017

A recombinant fungal compound induces anti-proliferative and pro-apoptotic effects on colon cancer cells.

Oncotarget 2017 Apr;8(17):28854-28864

The Robert H. Smith Faculty of Agriculture, Food and Environment, Institute of Biochemistry, Food Science and Nutrition, The Hebrew University of Jerusalem, Rehovot 76100, Israel.

Finding intracellular pathways and molecules that can prevent the proliferation of colon cancer cells can provide significant bases for developing treatments for this disease. Ostreolysin (Oly) is a protein found in the mushroom Pleurotus ostreatus, and we have produced a recombinant version of this protein (rOly).We measured the viability of several colon cancer cells treated with rOly. Xenografts and syngeneic colon cancer cells were injected into in vivo mouse models, which were then treated with this recombinant protein.rOly treatment induced a significant reduction in viability of human and mouse colon cancer cells. In contrast, there was no reduction in the viability of normal epithelial cells from the small intestine. In the search for cellular targets of rOly, we showed that it enhances the anti-proliferative activity of drugs targeting cellular tubulin. This was accompanied by a reduction in the weight and volume of tumours in mice injected with rOly as compared to their respective control mice in two in vivo models.Our results advance the functional understanding of rOly as a potential anti-cancer treatment associated with pro-apoptotic activities preferentially targeting colon cancer cells.
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http://dx.doi.org/10.18632/oncotarget.15859DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5438697PMC
April 2017

Toward combined delignification and saccharification of wheat straw by a laccase-containing designer cellulosome.

Proc Natl Acad Sci U S A 2016 09 12;113(39):10854-9. Epub 2016 Sep 12.

Department of Biomolecular Sciences, The Weizmann Institute of Science, Rehovot 76100, Israel;

Efficient breakdown of lignocellulose polymers into simple molecules is a key technological bottleneck limiting the production of plant-derived biofuels and chemicals. In nature, plant biomass degradation is achieved by the action of a wide range of microbial enzymes. In aerobic microorganisms, these enzymes are secreted as discrete elements in contrast to certain anaerobic bacteria, where they are assembled into large multienzyme complexes termed cellulosomes. These complexes allow for very efficient hydrolysis of cellulose and hemicellulose due to the spatial proximity of synergistically acting enzymes and to the limited diffusion of the enzymes and their products. Recently, designer cellulosomes have been developed to incorporate foreign enzymatic activities in cellulosomes so as to enhance lignocellulose hydrolysis further. In this study, we complemented a cellulosome active on cellulose and hemicellulose by addition of an enzyme active on lignin. To do so, we designed a dockerin-fused variant of a recently characterized laccase from the aerobic bacterium Thermobifida fusca The resultant chimera exhibited activity levels similar to the wild-type enzyme and properly integrated into the designer cellulosome. The resulting complex yielded a twofold increase in the amount of reducing sugars released from wheat straw compared with the same system lacking the laccase. The unorthodox use of aerobic enzymes in designer cellulosome machinery effects simultaneous degradation of the three major components of the plant cell wall (cellulose, hemicellulose, and lignin), paving the way for more efficient lignocellulose conversion into soluble sugars en route to alternative fuels production.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5047212PMC
http://dx.doi.org/10.1073/pnas.1608012113DOI Listing
September 2016

Limits of Versatility of Versatile Peroxidase.

Appl Environ Microbiol 2016 07 30;82(14):4070-4080. Epub 2016 Jun 30.

Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel

Unlabelled: Although Mn(2+) is the most abundant substrate of versatile peroxidases (VPs), repression of Pleurotus ostreatus vp1 expression occurred in Mn(2+)-sufficient medium. This seems to be a biological contradiction. The aim of this study was to explore the mechanism of direct oxidation by VP1 under Mn(2+)-deficient conditions, as it was found to be the predominant enzyme during fungal growth in the presence of synthetic and natural substrates. The native VP1 was purified and characterized using three substrates, Mn(2+), Orange II (OII), and Reactive Black 5 (RB5), each oxidized by a different active site in the enzyme. While the pH optimum for Mn(2+) oxidation is 5, the optimum pH for direct oxidation of both dyes was found to be 3. Indeed, effective in vivo decolorization occurred in media without addition of Mn(2+) only under acidic conditions. We have determined that Mn(2+) inhibits in vitro the direct oxidation of both OII and RB5 while RB5 stabilizes both Mn(2+) and OII oxidation. Furthermore, OII was found to inhibit the oxidation of both Mn(2+) and RB5. In addition, we could demonstrate that VP1 can cleave OII in two different modes. Under Mn(2+)-mediated oxidation conditions, VP1 was able to cleave the azo bond only in asymmetric mode, while under the optimum conditions for direct oxidation (absence of Mn(2+) at pH 3) both symmetric and asymmetric cleavages occurred. We concluded that the oxidation mechanism of aromatic compounds by VP1 is controlled by Mn(2+) and pH levels both in the growth medium and in the reaction mixture.

Importance: VP1 is a member of the ligninolytic heme peroxidase gene family of the white rot fungus Pleurotus ostreatus and plays a fundamental role in biodegradation. This enzyme exhibits a versatile nature, as it can oxidize different substrates under altered environmental conditions. VPs are highly interesting enzymes due to the fact that they contain unique active sites that are responsible for direct oxidation of various aromatic compounds, including lignin, in addition to the well-known Mn(2+) binding active site. This study demonstrates the limits of versatility of P. ostreatus VP1, which harbors multiple active sites, exhibiting a broad range of enzymatic activities, but they perform differently under distinct conditions. The versatility of P. ostreatus and its enzymes is an advantageous factor in the fungal ability to adapt to changing environments. This trait expands the possibilities for the potential utilization of P. ostreatus and other white rot fungi.
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http://dx.doi.org/10.1128/AEM.00743-16DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4959207PMC
July 2016

Biomimetic ferrichrome: structural motifs for switching between narrow- and broad-spectrum activities in P. putida and E. coli.

Dalton Trans 2015 Dec 13;44(48):20850-8. Epub 2015 Oct 13.

Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel.

A series of novel ferrichrome (FC) analogs was designed based on the X-ray structure of FC in the FhuA transporter of Escherichia coli. Two strategies were employed: the first strategy optimized the overall size and relative orientation of H-bonding interactions. The second strategy increased H-bonding interactions by introducing external H-donors onto analogs' backbone. Tris-amino templates were coupled to succinic or aspartic acid, and the second carboxyl was used for hydroxamate construction. Succinic acid provided analogs without substituents, whereas aspartic acid generated analogs with external amines (i.e. H-donors). All analogs had similar physicochemical properties, yet the biological activity in Pseudomonas putida and E. coli showed great variation. While some analogs targeted specifically P. putida, others were active in both strains thus exhibiting broad-spectrum activity (as in native FC). Narrow-spectrum or species-specificity might find application in microbial diagnostic kits, while broad-spectrum recognition may have advantages in therapeutics as siderophore-drug conjugates. The differences in the structure and range of microbial recognition helped us in formulating guidelines for minimal essential parameters required for inducing broad-spectrum activity.
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http://dx.doi.org/10.1039/c5dt02685gDOI Listing
December 2015

Transformation Pathways of the Recalcitrant Pharmaceutical Compound Carbamazepine by the White-Rot Fungus Pleurotus ostreatus: Effects of Growth Conditions.

Environ Sci Technol 2015 Oct 29;49(20):12351-62. Epub 2015 Sep 29.

Department of Analytical Chemistry, Helmholtz Centre for Environmental Research - UFZ , Permoserstrasse 15, 04318 Leipzig, Germany.

The widely used anticonvulsant pharmaceutical carbamazepine is recalcitrant in many environmental niches and thus poses a challenge in wastewater treatment. We followed the decomposition of carbamazepine by the white-rot fungus Pleurotus ostreatus in liquid culture compared to solid-state fermentation on lignocellulosic substrate where different enzymatic systems are active. Carbamazepine metabolites were identified using liquid chromatography-high-resolution mass spectrometry (LC-Q-TOF-MS). In liquid culture, carbamazepine was only transformed to 10,11-epoxy carbamazepine and 10,11-dihydroxy carbamazepine as a dead-end product. During solid-state fermentation, carbamazepine metabolism resulted in the generation of an additional 22 transformation products, some of which are toxic. Under solid-state-fermentation conditions, 10,11-epoxy carbamazepine was further metabolized via acridine and 10,11-dihydroxy carbamazepine pathways. The latter was further metabolized via five subpathways. When (14)C-carbonyl-labeled carbamazepine was used as the substrate, (14)C-CO2 release amounted to 17.4% of the initial radioactivity after 63 days of incubation. The proposed pathways were validated using metabolites (10,11-epoxy carbamazepine, 10,11-dihydroxy carbamazepine, and acridine) as primary substrates and following their fate at different time points. This work highlights the effect of growth conditions on the transformation pathways of xenobiotics. A better understanding of the fate of pollutants during bioremediation treatments is important for establishment of such technologies.
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http://dx.doi.org/10.1021/acs.est.5b02222DOI Listing
October 2015

Electrochemistry Combined with LC-HRMS: Elucidating Transformation Products of the Recalcitrant Pharmaceutical Compound Carbamazepine Generated by the White-Rot Fungus Pleurotus ostreatus.

Environ Sci Technol 2015 Oct 29;49(20):12342-50. Epub 2015 Sep 29.

Department of Analytical Chemistry, Helmholtz Centre for Environmental Research-UFZ , Permoserstrasse 15, Leipzig 04318, Germany.

Transformation products (TPs) of environmental pollutants must be identified to understand biodegradation processes and reaction mechanisms and to assess the efficiency of treatment processes. The combination of oxidation by an electrochemical cell (EC) with analysis by liquid chromatography-high-resolution mass spectrometry (LC-HRMS) is a rapid approach for the determination and identification of TPs generated by natural microbial processes. Electrochemically generated TPs of the recalcitrant pharmaceutical carbamazepine (CBZ) were used for a target screening for TPs formed by the white-rot fungus Pleurotus ostreatus. EC with LC-HRMS facilitates detection and identification of TPs because the product spectrum is not superimposed with biogenic metabolites and elevated substrate concentrations can be used. A group of 10 TPs formed in the microbial process were detected by target screening for molecular ions, and another 4 were detected by screening on the basis of characteristic fragment ions. Three of these TPs have never been reported before. For CBZ, EC with LC-HRMS was found to be more effective than software tools in defining targets for the screening and faster than nontarget screening alone in TP identification. EC with LC-HRMS may be used to feed MS databases with spectra of possible TPs of larger numbers of environmental contaminants for an efficient target screening.
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http://dx.doi.org/10.1021/acs.est.5b02229DOI Listing
October 2015

Seasonal effect and anthropogenic impact on the composition of the active bacterial community in Mediterranean orchard soil.

FEMS Microbiol Ecol 2015 Sep 6;91(9):fiv096. Epub 2015 Aug 6.

Department of Soil, Water, and Environmental Sciences, Agricultural Research Organization, Volcani Center, Bet-Dagan, 5025001, Israel

Several anthropogenic interventions, common in agriculture, may influence active bacterial communities in soil without affecting their total composition. Therefore, the composition of an active bacterial community in soil may reflect its relation to biogeochemical processes. This issue was addressed during two consecutive years in olive-orchard soil, irrigated with treated wastewater (TWW) in a Mediterranean climate, by following the active (rRNA) and total (rRNA gene) bacterial community in the soil. Although TWW irrigation did not affect the composition of the total soil bacterial community, it had an effect on the active fraction of the community. These results, based on 16S rRNA data, indicate that the organic matter and minerals in TWW were not directly utilized for the rapid proliferation of specific taxonomic groups. Activity levels, manifested by variance in the relative abundance of the active and total communities of selected operational taxonomic units, revealed annual and seasonal fluctuations and fluctuations dependent on the type of irrigation. The potential activity (nitrification rates) and community composition of ammonia-oxidizing bacteria were affected by TWW irrigation, and this group of bacteria was therefore further explored. It was concluded that irrigation with TWW had little effect on "who is there", i.e. which bacteria were present, but influenced "who is active", with a distinct effect on bacteria associated with the biochemical cycling of nitrogen.
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http://dx.doi.org/10.1093/femsec/fiv096DOI Listing
September 2015