Publications by authors named "Varda Zakin"

14 Publications

  • Page 1 of 1

Host Factors Modulating Ochratoxin A Biosynthesis during Fruit Colonization by .

J Fungi (Basel) 2020 Dec 28;7(1). Epub 2020 Dec 28.

Institute of Postharvest and Food Sciences, The Volcani Center, Agricultural Research Organization, Rishon LeZion 7528809, Israel.

is a strong and consistent ochratoxin A (OTA) producer and considered to be the main source of this toxic metabolite in grapes and grape products such as wine, grape juice and dried vine fruit. OTA is produced under certain growth conditions and its accumulation is affected by several environmental factors, such as growth phase, substrate, temperature, water activity and pH. In this study, we examined the impact of fruit host factors on regulation and accumulation of OTA in colonized grape berries, and assessed in vitro the impact of those factors on the transcriptional levels of the key genes and global regulators contributing to fungal colonization and mycotoxin synthesis. We found that limited sugar content, low pH levels and high malic acid concentrations activated OTA biosynthesis by , both in synthetic media and during fruit colonization, through modulation of global regulator of secondary metabolism, and OTA gene cluster expression. These findings indicate that fruit host factors may have a significant impact on the capability of to produce and accumulate OTA in grapes.
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http://dx.doi.org/10.3390/jof7010010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7823970PMC
December 2020

Functional roles of LaeA, polyketide synthase, and glucose oxidase in the regulation of ochratoxin A biosynthesis and virulence in Aspergillus carbonarius.

Mol Plant Pathol 2021 01 10;22(1):117-129. Epub 2020 Nov 10.

Institute of Postharvest and Food Sciences, The Volcani Center, Agricultural Research Organization, Rishon LeZion, Israel.

Aspergillus carbonarius is the major producer of ochratoxin A (OTA) among Aspergillus species, but the contribution of this secondary metabolite to fungal virulence has not been assessed. We characterized the functions and addressed the roles of three factors in the regulation of OTA synthesis and pathogenicity in A. carbonarius: LaeA, a transcriptional factor regulating the production of secondary metabolites; polyketide synthase, required for OTA biosynthesis; and glucose oxidase (GOX), regulating gluconic acid (GLA) accumulation and acidification of the host tissue during fungal growth. Deletion of laeA in A. carbonarius resulted in significantly reduced OTA production in colonized nectarines and grapes. The ∆laeA mutant was unable to efficiently acidify the colonized tissue, as a direct result of diminished GLA production, leading to attenuated virulence in infected fruit compared to the wild type (WT). The designed Acpks-knockout mutant resulted in complete inhibition of OTA production in vitro and in colonized fruit. Interestingly, physiological analysis revealed that the colonization pattern of the ∆Acpks mutant was similar to that of the WT strain, with high production of GLA in the colonized tissue, suggesting that OTA accumulation does not contribute to A. carbonarius pathogenicity. Disruption of the Acgox gene inactivated GLA production in A. carbonarius, and this mutant showed attenuated virulence in infected fruit compared to the WT strain. These data identify the global regulator LaeA and GOX as critical factors modulating A. carbonarius pathogenicity by controlling transcription of genes important for fungal secondary metabolism and infection.
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http://dx.doi.org/10.1111/mpp.13013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7749749PMC
January 2021

The pH-Responsive Transcription Factor PacC Governs Pathogenicity and Ochratoxin A Biosynthesis in .

Front Microbiol 2020 13;11:210. Epub 2020 Feb 13.

Institute of Postharvest and Food Sciences, Agricultural Research Organization, Volcani Center, Rishon LeZion, Israel.

Pathogenic fungi must respond effectively to changes in environmental pH for successful host colonization, virulence and toxin production. is a mycotoxigenic pathogen with the ability to colonize many plant hosts and secrete ochratoxin A (OTA). In this study, we characterized the functions and addressed the role of PacC-mediated pH signaling in pathogenicity using designed gene knockout mutant. Δ mutant displayed an acidity-mimicking phenotype, which resulted in impaired fungal growth at neutral/alkaline pH, accompanied by reduced sporulation and conidial germination compared to the wild type (WT) strain. The Δ mutant was unable to efficiently acidify the growth media as a direct result of diminished gluconic and citric acid production. Furthermore, loss of resulted in a complete inhibition of OTA production at pH 7.0. Additionally, Δ mutant exhibited attenuated virulence compared to the WT toward grapes and nectarine fruits. Reintroduction of gene into Δ mutant restored the WT phenotype. Our results demonstrate important roles of PacC of in OTA biosynthesis and in pathogenicity by controlling transcription of genes important for fungal secondary metabolism and infection.
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http://dx.doi.org/10.3389/fmicb.2020.00210DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7031272PMC
February 2020

Synergistic Inhibition of Mycotoxigenic Fungi and Mycotoxin Production by Combination of Pomegranate Peel Extract and Azole Fungicide.

Front Microbiol 2019 20;10:1919. Epub 2019 Aug 20.

Department of Food Quality and Safety, Institute for Postharvest and Food Sciences, Agricultural Research Organization, The Volcani Center, Rishon LeZion, Israel.

Fungal plant pathogens cause considerable losses in yield and quality of field crops worldwide. In addition, under specific environmental conditions, many fungi, including such as some and spp., are further able to produce mycotoxins while colonizing their host, which accumulate in human and animal tissues, posing a serious threat to consumer health. Extensive use of azole fungicides in crop protection stimulated the emergence of acquired azole resistance in some plant and human fungal pathogens. Combination treatments, which become popular in clinical practice, offer an alternative strategy for managing potentially resistant toxigenic fungi and reducing the required dosage of specific drugs. In the current study we tested the effect of pomegranate peel extract (PPE) on the growth and toxin production of the mycotoxigenic fungi and , both alone and in combination with the azole fungicide prochloraz (PRZ). Using time-lapse microscopy and quantitative image analysis we demonstrate significant delay of conidial germination and hyphal elongation rate in both fungi following PPE treatment in combination with PRZ. Moreover, PPE treatment reduced aflatoxin production by up to 97%, while a combined treatment with sub-inhibitory doses of PPE and PRZ resulted in complete inhibition of toxin production over a 72 h treatment. These findings were supported by qRT-PCR analysis, showing down-regulation of key genes involved in the aflatoxin biosynthetic pathway under combined PPE/PRZ treatment al low concentrations. Our results provide first evidence for synergistic effects between the commercial drug PRZ and natural compound PPE. Future application of these findings may allow to reduce the required dosage of PRZ, and possibly additional azole drugs, to inhibit mycotoxigenic fungi, ultimately reducing potential concerns over exposure to high doses of these potentially harmful fungicides.
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http://dx.doi.org/10.3389/fmicb.2019.01919DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6710344PMC
August 2019

N-Halamine Derivatized Nanoparticles with Selective Cyanocidal Activity: Potential for Targeted Elimination of Harmful Cyanobacterial Blooms.

Environ Sci Technol 2019 Aug 22;53(15):9160-9170. Epub 2019 Jul 22.

Department of Food Science, Institute of Postharvest and Food Sciences , Agricultural Research Organization, The Volcani Center , Rishon LeZion 7528809 , Israel.

Harmful cyanobacterial blooms (HCBs) are becoming a major challenge for the management of both natural and man-made freshwater lakes and reservoirs. Phytoplankton communities are an essential component of aquatic ecosystems, providing the basis for natural food webs as well as important environmental services. HCBs, driven by a combination of environmental pollution and rising global temperatures, destabilize phytoplankton communities with major impacts on aquatic ecology and trophic interactions. Application of currently available algaecides generally results in unselective elimination of phytoplankton species, disrupting water ecology and environmental services provided by beneficial algae. There is thus a need for selective cyanocidal compounds that can eliminate cyanobacteria while preserving algal members of the phytoplankton community. Here, we demonstrate the efficacy of N-halamine derivatized nanoparticles (Cl NPs) in selectively eliminating cyanobacteria, including the universal bloom-forming species , while having minimal effect on co-occurring algal species. We further support these results with the use a simple microfluidic platform in combination with advanced live-imaging microscopy to study the effects of Cl NPs on both laboratory cultures and natural populations of cyanobacteria and algae at single cell resolutions. We note that the Cl NPs used in this work were made of polymethacrylamide, a nonbiodegradable polymer that may be unsuitable for use as a cyanocide in open aquatic environments. Nevertheless, the demonstrated selective action of these Cl NPs suggests a potential for developing alternative, biodegradable carriers with similar properties as future cyanocidal agents that will enable selective elimination of HCBs.
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http://dx.doi.org/10.1021/acs.est.9b01368DOI Listing
August 2019

Shifts in the Composition of the Microbiota of Stored Wheat Grains in Response to Fumigation.

Front Microbiol 2019 17;10:1098. Epub 2019 May 17.

Institute of Postharvest and Food Sciences, Agricultural Research Organization - The Volcani Center, Rishon LeZion, Israel.

While the wheat-associated microbiome is of major agricultural importance, little is known about the alterations in wheat grain microbial community composition during storage. Characterization of the bacterial and fungal communities in stored wheat grains revealed the impact of phosphine fumigation, one of the most effective methods to eliminate insects in stored commodities, on the composition of the wheat grain microbiome. High-throughput amplicon sequencing of the bacterial 16S rRNA gene and fungal internal transcribed spacer (ITS) region was used to analyze the wheat grain microbiome at different times over as 6 months period of storage. Higher bacterial diversity was found across the samples during the first (immediately after harvest) and second (3 months later) time points, with a predominance of , , , and . A two-fold decrease in the number of bacterial operational taxonomic units (OTUs) was observed in wheat grains at the last time point (6 months later), following phosphine treatment. In contrast to the effect of phosphine on bacteria, it did not affect fungal diversity in stored grains. The majority of fungal sequences were assigned to , followed by , , and unidentified fungi, which were evenly distributed throughout the storage period. Alpha and beta diversity analyses were confirmed by examination of the cultured microbial taxa obtained from the stored wheat grains. Mycotoxin analysis of wheat grains collected after phosphine fumigation revealed the presence of toxins, primarily deoxynivalenol (DON). Several mycotoxigenic spp. were also detected in the same samples. Results of the present study indicate that microbiome of stored, whole wheat grains was strongly affected by phosphine fumigation, which changed the structure of the microbial community leading to shifts in species composition toward mycotoxigenic strains. A better understanding of the complex interactions within the microbial communities of stored grains will assist in the development of novel biocontrol strategies to overcome mycotoxin contamination.
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http://dx.doi.org/10.3389/fmicb.2019.01098DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6533538PMC
May 2019

Rapid Detection and Identification of Mycotoxigenic Fungi and Mycotoxins in Stored Wheat Grain.

Toxins (Basel) 2017 09 25;9(10). Epub 2017 Sep 25.

Department of Food Quality and Safety, Institute for Postharvest and Food Sciences, Agricultural Research Organization, The Volcani Center, Rishon LeZion 7528809, Israel.

This study aimed to assess the occurrence of toxigenic fungi and mycotoxin contamination in stored wheat grains by using advanced molecular and analytical techniques. A multiplex polymerase chain reaction (PCR) strategy was established for rapid identification of mycotoxigenic fungi, and an improved analytical method was developed for simultaneous multi-mycotoxin determination in wheat grains by liquid chromatography-tandem mass spectrometry (LC/MS/MS) without the need for any clean-up. The optimized multiplex PCR method was highly specific in detecting fungal species containing species-specific and mycotoxin metabolic pathway genes. The method was applied for evaluation of 34 wheat grain samples collected from storage warehouses for the presence of mycotoxin-producing fungi, and a few samples were found positive for and species. Further chemical analysis revealed that 17 samples contained mycotoxins above the level of detection, but only six samples were found to be contaminated over the EU regulatory limits with at least one mycotoxin. Aflatoxin B₁, fumonisins, and deoxynivalenol were the most common toxins found in these samples. The results showed a strong correlation between the presence of mycotoxin biosynthesis genes as analyzed by multiplex PCR and mycotoxin detection by LC/MS/MS. The present findings indicate that a combined approach might provide rapid, accurate, and sensitive detection of mycotoxigenic species and mycotoxins in wheat grains.
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http://dx.doi.org/10.3390/toxins9100302DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5666349PMC
September 2017

Bioinspired passive anti-biofouling surfaces preventing biofilm formation.

J Mater Chem B 2015 Feb 14;3(7):1371-1378. Epub 2015 Jan 14.

Department of Materials Science and Engineering, Technion Israel Institute of Technology, 32000 Haifa, Israel.

Biofilm formation enables bacteria to grow under unfavorable conditions, provides them with protection, and increases their resistance to antimicrobial agents. Once a biofilm has formed, it is difficult, and in some systems, impossible to treat. Strategies based on the release of biocidal agents have shown only transient efficiency. Herein, we present a novel bioinspired passive approach to the prevention of surface biofilm attachment by exploiting superhydrophobic surfaces formed via the self-assembly of paraffin or fluorinated wax crystals. Our surfaces show exceptional ability to inhibit biofilm formation of both Gram-positive Bacillus cereus and Gram-negative Pseudomonas aeruginosa over a 7 day period (up to 99.9% inhibition).
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http://dx.doi.org/10.1039/c4tb01522cDOI Listing
February 2015

External pH is a cue for the behavioral switch that determines surface motility and biofilm formation of Alicyclobacillus acidoterrestris.

J Food Prot 2014 Aug;77(8):1418-23

Department of Food Quality and Safety, Institute for Postharvest Technology and Food Sciences, Agricultural Research Organization (ARO), The Volcani Center, P.O. Box 6, Bet-Dagan 50250, Israel.

Bacteria use different strategies to survive unfavorable environmental conditions. Alicyclobacillus acidoterrestris is a bacterium capable of surviving extremely harsh conditions, for instance, during industrial food processing. A. acidoterrestris is a spore-forming, thermoacidophilic, nonpathogenic bacterium that commonly contaminates commercial pasteurized fruit juices and is, therefore, considered a major microbiological contaminant in the juice industry. The purpose of this study was to elucidate whether A. acidoterrestris is capable of multicellular behavior by testing its ability of biofilm formation and surface motility. A. acidoterrestris was found to be proficient in migration over a surface that is apparently powered by flagella. It was further shown that lowering the external pH leads to inhibition in surface motility of these bacteria. Concomitantly, the reduction in the external pH triggered biofilm formation of A. acidoterrestris cells. Thus, although no significant biofilm was formed at pH 4.5, robust cell adhesion and confluent biofilm formation was seen below the pH 3.6. These findings indicate that the reduction of external pH is an environmental cue for the behavioral switch that inhibits surface motility and triggers biofilm formation of A. acidoterrestris. Gaining insight into the multicellular behavior that facilitates A. acidoterrestris survival in food contact surfaces may contribute to the development of novel antimicrobial means to prevent cross-contamination caused by this bacterium.
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http://dx.doi.org/10.4315/0362-028X.JFP-13-425DOI Listing
August 2014

Butyric acid released during milk lipolysis triggers biofilm formation of Bacillus species.

Int J Food Microbiol 2014 Jul 22;181:19-27. Epub 2014 Apr 22.

Department of Food Quality and Safety, Agricultural Research Organization (ARO), Bet-Dagan, Israel. Electronic address:

Bacillus species form biofilms within milking pipelines and on surfaces of equipment in the dairy industry which represent a continuous hygiene problem and can lead to serious economic losses due to food spoilage and equipment impairment. Although much is known about the mechanism by which the model organism Bacillus subtilis forms biofilms in laboratory mediums in vitro, little is known of how these biofilms are formed in natural environments such as milk. Besides, little is known of the signaling pathways leading to biofilm formation in other Bacillus species, such as Bacillus cereus and Bacillus licheniformis, both of which are known to contaminate milk. In this study, we report that milk triggers the formation of biofilm-related structures, termed bundles. We show this to be a conserved phenomenon among all Bacillus members tested. Moreover, we demonstrate that the tasA gene, which encodes a major portion of the matrix which holds the biofilm together, is vital for this process. Furthermore, we show that the free fatty acid (FFA) - butyric acid (BA), which is released during lipolysis of milk fat and demonstrates antimicrobial activity, is the potent trigger for biofilm bundle formation. We finally show that BA-triggered biofilm bundle formation is mediated by the histidine kinase, KinD. Taken together, these observations indicate that BA, which is a major FFA within milk triggers biofilm formation in a conserved mechanism among members of the Bacillus genus.
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http://dx.doi.org/10.1016/j.ijfoodmicro.2014.04.013DOI Listing
July 2014

Durable contact active antimicrobial materials formed by a one-step covalent modification of polyvinyl alcohol, cellulose and glass surfaces.

Colloids Surf B Biointerfaces 2013 Dec 2;112:356-61. Epub 2013 Aug 2.

Department of Food Quality and Safety, Agricultural Research Organization, The Volcani Center, Bet-Dagan 50250, Israel. Electronic address:

In this work we have applied a direct covalent linkage of quaternary ammonium salts (QAS) to prepare a series of contact active antimicrobial surfaces based on widely utilized materials. Formation of antimicrobial polyvinyl alcohol (PVA-QAS), cellulose (cellulose-QAS) and glass (glass-QAS) surfaces was achieved by one step synthesis with no auxiliary linkers. The X-ray photoelectron spectroscopy (XPS) revealed tridentate binding mode of the antimicrobial agent. The antimicrobial activity of the prepared materials was tested on Bacillus cereus, Alicyclobacillus acidoterrestris, Escherichia coli and Pseudomonas aeruginosa. Active site density of the modified materials was examined and found to correlate with their antimicrobial activity. Stability studies at different pH values and temperatures confirmed that the linkage of the bioactive moiety to the surface is robust and resistant to a range of pH and temperatures. Prolonged long-term effectiveness of the contact active materials was demonstrated by their repeated usage, without loss of the antimicrobial efficacy.
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http://dx.doi.org/10.1016/j.colsurfb.2013.07.032DOI Listing
December 2013

Draft Genome Sequence of Alicyclobacillus acidoterrestris Strain ATCC 49025.

Genome Announc 2013 Sep 5;1(5). Epub 2013 Sep 5.

Department of Food Quality and Safety, Agricultural Research Organization The Volcani Center, Bet-Dagan, Israel.

Alicyclobacillus acidoterrestris is a spore-forming Gram-positive, thermo-acidophilic, nonpathogenic bacterium which contaminates commercial pasteurized fruit juices. The draft genome sequence for A. acidoterrestris strain ATCC 49025 is reported here, providing genetic data relevant to the successful adaptation and survival of this strain in its ecological niche.
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http://dx.doi.org/10.1128/genomeA.00638-13DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3764408PMC
September 2013

Scientific evidence of the therapeutic effects of dead sea treatments: a systematic review.

Semin Arthritis Rheum 2012 Oct 12;42(2):186-200. Epub 2012 Apr 12.

Maccabi Healthcare Services, Tel Aviv, Israel.

Objectives: The Dead Sea, the deepest and most saline lake on earth, has been known from biblical times for its healing properties. The aim of this systematic review was to present critically the level of evidence for the claims of therapeutic effects of Dead Sea treatments in several rheumatologic diseases and psoriasis as well as to review these treatments' safety.

Methods: All articles cited in MEDLINE under the query, "Dead Sea," were reviewed.

Results: We found bona fide evidence that Dead Sea treatments are especially effective in psoriasis due to both the special characteristics of solar ultraviolet radiation in the Dead Sea and the Dead Sea water balneotherapy. Dead Sea mud and Dead Sea balneotherapy have been found to be beneficial in rheumatologic diseases, including rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, and knee osteoarthritis. In the safety analysis, we found no evidence for an increase in skin neoplasia, although skin actinic damage seems to be increased in patients treated in the Dead Sea. Dead Sea treatments do not lead to worsening of blood pressure. Substantial ingestion of Dead Sea water (generally in unusual near-drowning cases) is toxic and can result in cardiac rhythm disturbances because of electrolyte concentration abnormalities. Laboratory analysis of Dead Sea mud did not reveal mineral concentrations that could represent a health concern for their intended use.

Conclusions: Dead Sea treatments are beneficial in several rheumatologic diseases and psoriasis and have a good safety profile.
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http://dx.doi.org/10.1016/j.semarthrit.2012.02.006DOI Listing
October 2012

Two different propionicins produced by Propionibacterium thoenii P-127.

Peptides 2003 Nov;24(11):1733-40

Department of Food Science, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet-Dagan 50250, Israel.

The bacteriocin GBZ-1 was purified from the growth media of Propionibacterium thoenii P-127 and was found to have a molecular weight of 6000Da. P. thoenii P-127 also known as the producer of the bacteriocin PLG-1 (MW 10kDa). Under specific growth conditions, on semi-solid media, P. thoenii P-127 produced both PLG-1 and GBZ-1. The N-terminal of GBZ-1 was microsequenced, the gene was cloned and the DNA sequence was determined and identified. GBZ-1 is highly homologous to a protease-activated antimicrobial peptide (PAMP). In contrast to PAMP, it was purified in its active form and no protease digestion was required for its activation. The survival curve of indicator bacteria Lactobacillus delbrueckii subsp. lactic ATCC 4797 showed two phases. The fast phase of 20min was followed by a slow phase. While bacterial survival was reduced by 2logs during the fast phase, bacterial survival was reduced by additional 3logs up to 200min during the slow phase. GBZ-1 activity was affected by magnesium and its activity was completely abolished at 50mM magnesium chloride. Other divalent cations had no effect on GBZ-1 activity of GBZ-1. To the best of our knowledge this is the first report of a bacterium producing two different bacteriocins under different growth conditions.
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http://dx.doi.org/10.1016/j.peptides.2003.08.018DOI Listing
November 2003