Publications by authors named "Linda S Thomashow"

64 Publications

Global landscape of phenazine biosynthesis and biodegradation reveals species-specific colonization patterns in agricultural soils and crop microbiomes.

Elife 2020 09 15;9. Epub 2020 Sep 15.

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, United States.

Phenazines are natural bacterial antibiotics that can protect crops from disease. However, for most crops it is unknown which producers and specific phenazines are ecologically relevant, and whether phenazine biodegradation can counter their effects. To better understand their ecology, we developed and environmentally-validated a quantitative metagenomic approach to mine for phenazine biosynthesis and biodegradation genes, applying it to >800 soil and plant-associated shotgun-metagenomes. We discover novel producer-crop associations and demonstrate that phenazine biosynthesis is prevalent across habitats and preferentially enriched in rhizospheres, whereas biodegrading bacteria are rare. We validate an association between maize and , a putative producer abundant in crop microbiomes. upregulates phenazine biosynthesis during phosphate limitation and robustly colonizes maize seedling roots. This work provides a global picture of phenazines in natural environments and highlights plant-microbe associations of agricultural potential. Our metagenomic approach may be extended to other metabolites and functional traits in diverse ecosystems.
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http://dx.doi.org/10.7554/eLife.59726DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7591250PMC
September 2020

Proteomics Reveals the Changes that Contribute to Fusarium Head Blight Resistance in Wheat.

Phytopathology 2021 Feb 21;111(2):386-397. Epub 2020 Dec 21.

College of Agronomy, Northwest A&F University, Yangling 712100, People's Republic of China.

Fusarium head blight (FHB) is a devastating disease of wheat, causing yield losses and quality reduction as a result of mycotoxin production. In this study, iTRAQ (isobaric tags for relative and absolute quantification)-labeling-based mass spectrometry was employed to characterize the proteome in wheat cultivars Xinong 538 and Zhoumai 18 with contrasting levels of FHB resistance as a means to elucidate the molecular mechanisms contributing to FHB resistance. A total of 13,669 proteins were identified in the two cultivars 48 h after inoculation. Among these, 2,505 unique proteins exclusively accumulated in Xinong 538 (resistant) and 887 proteins in Zhoumai 18 (susceptible). Gene Ontology enrichment analysis showed that most differentially accumulated proteins (DAPs) from both cultivars were assigned to the following categories: metabolic process, single-organism process, cellular process, and response to stimulus. Kyoto Encyclopedia of Genes and Genomes analysis showed that a greater number of proteins belonging to different metabolic pathways were identified in Xinong 538 compared with Zhoumai 18. Specifically, DAPs from the FHB-resistant cultivar Xinong 538 populated categories of metabolic pathways related to plant-pathogen interaction. These DAPs might play a critical role in defense responses exhibited by Xinong 538. DAPs from both genotypes were assigned to all wheat chromosomes except chromosome 6B, with approximately 30% mapping to wheat chromosomes 2B, 3B, 5B, and 5D. Twenty single nucleotide polymorphism markers, flanking DAPs on chromosomes 1B, 3B, 5B, and 6A, overlapped with the location of earlier mapped FHB-resistance quantitative trait loci. The data provide evidence for the involvement of several DAPs in the early stages of the FHB-resistance response in wheat; however, further functional characterization of candidate proteins is warranted.
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http://dx.doi.org/10.1094/PHYTO-05-20-0171-RDOI Listing
February 2021

Predicting disease occurrence with high accuracy based on soil macroecological patterns of Fusarium wilt.

ISME J 2020 Dec 17;14(12):2936-2950. Epub 2020 Jul 17.

The Key Laboratory of Plant Immunity, Jiangsu Provincial Key Lab for Organic Solid Waste Utilization, National Engineering Research Center for Organic-based Fertilizers, Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, Nanjing Agricultural University, Nanjing, 210095, China.

Soil-borne plant diseases are increasingly causing devastating losses in agricultural production. The development of a more refined model for disease prediction can aid in reducing crop losses through the use of preventative control measures or soil fallowing for a planting season. The emergence of high-throughput DNA sequencing technology has provided unprecedented insight into the microbial composition of diseased versus healthy soils. However, a single independent case study rarely yields a general conclusion predictive of the disease in a particular soil. Here, we attempt to account for the differences among various studies and plant varieties using a machine-learning approach based on 24 independent bacterial data sets comprising 758 samples and 22 independent fungal data sets comprising 279 samples of healthy or Fusarium wilt-diseased soils from eight different countries. We found that soil bacterial and fungal communities were both clearly separated between diseased and healthy soil samples that originated from six crops across nine countries or regions. Alpha diversity was consistently greater in the fungal community of healthy soils. While diseased soil microbiomes harbored higher abundances of Xanthomonadaceae, Bacillaceae, Gibberella, and Fusarium oxysporum, the healthy soil microbiome contained more Streptomyces Mirabilis, Bradyrhizobiaceae, Comamonadaceae, Mortierella, and nonpathogenic fungi of Fusarium. Furthermore, a random forest method identified 45 bacterial OTUs and 40 fungal OTUs that categorized the health status of the soil with an accuracy >80%. We conclude that these models can be applied to predict the potential for occurrence of F. oxysporum wilt by revealing key biological indicators and features common to the wilt-diseased soil microbiome.
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http://dx.doi.org/10.1038/s41396-020-0720-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7784920PMC
December 2020

Genome-Wide Identification and Expression Profile Analysis of the Phospholipase C Gene Family in Wheat ( L.).

Plants (Basel) 2020 Jul 13;9(7). Epub 2020 Jul 13.

College of Agronomy, Northwest A&F University, Yangling 712100, China.

Phospholipid-hydrolyzing enzymes include members of the phospholipase C (PLC) family that play important roles in regulating plant growth and responding to stress. In the present study, a systematic in silico analysis of the wheat gene family revealed a total of 26 wheat genes (s). Phylogenetic and sequence alignment analyses divided the wheat PLC genes into 2 subfamilies, (containing the typical X, Y, and C2 domains) and (containing a phosphatase domain). expression patterns differed among tissues, organs, and under abiotic stress conditions. The transcript levels of 8 genes were validated through qPCR analyses. Most of the genes were sensitive to salt stress and were up-regulated rapidly, and some were sensitive to low temperatures and drought. Overexpression of significantly improved resistance to salt and drought stress in , and the primary root of P1-OE was significantly longer than that of the wild type under stress conditions. Our results not only provide comprehensive information for understanding the gene family in wheat, but can also provide a solid foundation for functional characterization of the wheat PLC gene family.
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http://dx.doi.org/10.3390/plants9070885DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7412115PMC
July 2020

2-79 Transformed with Pyrrolnitrin Biosynthesis Genes Has Improved Biocontrol Activity Against Soilborne Pathogens of Wheat and Canola.

Phytopathology 2020 May 24;110(5):1010-1017. Epub 2020 Mar 24.

U.S. Department of Agriculture-Agriculture Research Service, Wheat Health, Genetics and Quality Research Unit, Pullman, WA 99164-6430, U.S.A.

A four-gene operon () from Pf-5 encoding the biosynthesis of the antibiotic pyrronitrin was introduced into (formerly ) 2-79, an aggressive root colonizer of both dryland and irrigated wheat roots that naturally produces the antibiotic phenazine-1-carboxylic acid and suppresses both take-all and Rhizoctonia root rot of wheat. Recombinant strains ZHW15 and ZHW25 produced both antibiotics and maintained population sizes in the rhizosphere of wheat that were comparable to those of strain 2-79. The recombinant strains inhibited in vitro the wheat pathogens anastomosis group 8 (AG-8) and AG-2-1, var. , , , and significantly more than did strain 2-79. Both the wild-type and recombinant strains were equally inhibitory of . When applied as a seed treatment, the recombinant strains suppressed take-all, Rhizoctonia root rot of wheat, and Rhizoctonia root and stem rot of canola significantly better than did wild-type strain 2-79.
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http://dx.doi.org/10.1094/PHYTO-09-19-0367-RDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7238759PMC
May 2020

Exploring the Pathogenicity of Q8r1-96 and Other Strains of the Complex on Tomato.

Plant Dis 2020 Apr 29;104(4):1026-1031. Epub 2020 Jan 29.

U.S. Department of Agriculture, Agricultural Research Service, Wheat Health, Genetics and Quality Research Unit, Pullman, WA 99164-6430, U.S.A.

and related species of the complex have long been studied as biocontrol and growth-promoting rhizobacteria involved in suppression of soilborne pathogens. We report here that Q8r1-96 and other 2,4-diacetylphloroglucinol (DAPG)-producing fluorescent pseudomonads involved in take-all decline of wheat in the Pacific Northwest of the United States can also be pathogenic to other plant hosts. Strain Q8r1-96 caused necrosis when injected into tomato stems and immature tomato fruits, either attached or removed from the plant, but lesion development was dose dependent, with a minimum of 10 CFU ml required to cause visible tissue damage. We explored the relative contribution of several known plant-microbe interaction traits to the pathogenicity of strain Q8r1-96. Type III secretion system (T3SS) mutants of Q8r1-96, injected at a concentration of 10 CFU ml, were significantly less virulent, but not consistently, as compared with the wild-type strain. However, a DAPG-deficient mutant of Q8r1-96 was significantly and consistently less virulent as compared with the wild type. Strain Q8r1-96acc, engineered to over express ACC deaminase, caused a similar amount of necrosis as the wild type. Cell-free culture filtrates of strain Q8r1-96 and pure DAPG also cause necrosis in tomato fruits. Our results suggest that DAPG plays a significant role in the ability of Q8r1-96 to cause necrosis of tomato tissue, but other factors also contribute to the pathogenic properties of this organism.
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http://dx.doi.org/10.1094/PDIS-09-19-1989-REDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7163159PMC
April 2020

Phenazine-1-Carboxylic Acid-Producing Bacteria Enhance the Reactivity of Iron Minerals in Dryland and Irrigated Wheat Rhizospheres.

Environ Sci Technol 2019 12 5;53(24):14273-14284. Epub 2019 Dec 5.

United State Department of Agriculture - Agricultural Research Service , Wheat Health, Genetics and Quality Research Unit , Pullman , Washington 99164-6430 , United States.

Phenazine-1-carboxylic acid (PCA) is a broad-spectrum antibiotic produced by rhizobacteria in the dryland wheat fields of the Columbia Plateau. PCA and other phenazines reductively dissolve Fe and Mn oxyhydroxides in bacterial culture systems, but the impact of PCA upon Fe and Mn cycling in the rhizosphere is unknown. Here, concentrations of dithionite-extractable and poorly crystalline Fe were approximately 10% and 30-40% higher, respectively, in dryland and irrigated rhizospheres inoculated with the PCA-producing (PCA) strain 2-79 than in rhizospheres inoculated with a PCA-deficient mutant. However, rhizosphere concentrations of Fe(II) and Mn did not differ significantly, indicating that PCA-mediated redox transformations of Fe and Mn were transient or were masked by competing processes. Total Fe and Mn uptake into wheat biomass also did not differ significantly, but the PCA strain significantly altered Fe translocation into shoots. X-ray absorption near edge spectroscopy revealed an abundance of Fe-bearing oxyhydroxides and phyllosilicates in all rhizospheres. These results indicate that the PCA strain enhanced the reactivity and mobility of Fe derived from soil minerals without producing parallel changes in plant Fe uptake. This is the first report that directly links significant alterations of Fe-bearing minerals in the rhizosphere to a single bacterial trait.
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http://dx.doi.org/10.1021/acs.est.9b03962DOI Listing
December 2019

A mutualistic interaction between Streptomyces bacteria, strawberry plants and pollinating bees.

Nat Commun 2019 10 22;10(1):4802. Epub 2019 Oct 22.

Department of Plant Medicine and Institute of Agriculture and Life Science, Gyeongsang National University, Jinju, 52828, Republic of Korea.

Microbes can establish mutualistic interactions with plants and insects. Here we track the movement of an endophytic strain of Streptomyces bacteria throughout a managed strawberry ecosystem. We show that a Streptomyces isolate found in the rhizosphere and on flowers protects both the plant and pollinating honeybees from pathogens (phytopathogenic fungus Botrytis cinerea and pathogenic bacteria, respectively). The pollinators can transfer the Streptomyces bacteria among flowers and plants, and Streptomyces can move into the plant vascular bundle from the flowers and from the rhizosphere. Our results present a tripartite mutualism between Streptomyces, plant and pollinator partners.
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http://dx.doi.org/10.1038/s41467-019-12785-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6805876PMC
October 2019

Root-associated microbes in sustainable agriculture: models, metabolites and mechanisms.

Pest Manag Sci 2019 Sep 19;75(9):2360-2367. Epub 2019 Apr 19.

USDA, Agricultural Research Service, Wheat Health, Genetics and Quality Research Unit, Department of Plant Pathology, Washington State University, Pullman, WA, USA.

Since the discovery of penicillin in 1928 and throughout the 'age of antibiotics' from the 1940s until the 1980s, the detection of novel antibiotics was restricted by lack of knowledge about the distribution and ecology of antibiotic producers in nature. The discovery that a phenazine compound produced by Pseudomonas bacteria could suppress soilborne plant pathogens, and its recovery from rhizosphere soil in 1990, provided the first incontrovertible evidence that natural metabolites could control plant pathogens in the environment and opened a new era in biological control by root-associated rhizobacteria. More recently, the advent of genomics, the availability of highly sensitive bioanalytical instrumentation, and the discovery of protective endophytes have accelerated progress toward overcoming many of the impediments that until now have limited the exploitation of beneficial plant-associated microbes to enhance agricultural sustainability. Here, we present key developments that have established the importance of these microbes in the control of pathogens, discuss concepts resulting from the exploration of classical model systems, and highlight advances emerging from ongoing investigations. © 2019 Society of Chemical Industry.
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http://dx.doi.org/10.1002/ps.5406DOI Listing
September 2019

Diversity of phytobeneficial traits revealed by whole-genome analysis of worldwide-isolated phenazine-producing Pseudomonas spp.

Environ Microbiol 2019 01 17;21(1):437-455. Epub 2018 Dec 17.

Department of Biology, Université de Moncton, Moncton, NB, Canada.

Plant-beneficial Pseudomonas spp. competitively colonize the rhizosphere and display plant-growth promotion and/or disease-suppression activities. Some strains within the P. fluorescens species complex produce phenazine derivatives, such as phenazine-1-carboxylic acid. These antimicrobial compounds are broadly inhibitory to numerous soil-dwelling plant pathogens and play a role in the ecological competence of phenazine-producing Pseudomonas spp. We assembled a collection encompassing 63 strains representative of the worldwide diversity of plant-beneficial phenazine-producing Pseudomonas spp. In this study, we report the sequencing of 58 complete genomes using PacBio RS II sequencing technology. Distributed among four subgroups within the P. fluorescens species complex, the diversity of our collection is reflected by the large pangenome which accounts for 25 413 protein-coding genes. We identified genes and clusters encoding for numerous phytobeneficial traits, including antibiotics, siderophores and cyclic lipopeptides biosynthesis, some of which were previously unknown in these microorganisms. Finally, we gained insight into the evolutionary history of the phenazine biosynthetic operon. Given its diverse genomic context, it is likely that this operon was relocated several times during Pseudomonas evolution. Our findings acknowledge the tremendous diversity of plant-beneficial phenazine-producing Pseudomonas spp., paving the way for comparative analyses to identify new genetic determinants involved in biocontrol, plant-growth promotion and rhizosphere competence.
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http://dx.doi.org/10.1111/1462-2920.14476DOI Listing
January 2019

Construction of a proteome reference map and response of Gaeumannomyces graminis var. tritici to 2,4-diacetylphloroglucinol.

Fungal Biol 2018 11 17;122(11):1098-1108. Epub 2018 Sep 17.

Division of Applied Life Science (BK21Plus) and Institute of Agriculture & Life Sciences, Gyeongsang National University, Jinju 52828, Republic of Korea. Electronic address:

Take-all disease, caused by Gaeumannomyces graminis var. tritici (Ggt), is one of the most serious root diseases in wheat production. In this study, a proteomic platform based on 2-dimensional gel electrophoresis (2-DE) and Matrix-Assisted Laser Desorption/Ionization Time of Flight Tandem Mass Spectrometry (MALDI-TOF/TOF MS) was used to construct the first proteome database reference map of G. graminis var. tritici and to identify the response of the pathogen to 2,4-diacetylphloroglucinol (DAPG), which is a natural antibiotic produced by antagonistic Pseudomonas spp. in take-all suppressive soils. For mapping, a total of 240 spots was identified that represented 209 different proteins. The most abundant biological function categories in the Ggt proteome were related to carbohydrate metabolism (21%), amino acid metabolism (15%), protein folding and degradation (12%), translation (11%), and stress response (10%). In total, 51 Ggt proteins were affected by DAPG treatment. Based on gene ontology, carbohydrate metabolism, amino acid metabolism, stress response, and protein folding and degradation proteins were the ones most modulated by DAPG treatment. This study provides the first extensive proteomic reference map constructed for Ggt and represents the first time that the response of Ggt to DAPG has been characterized at the proteomic level.
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http://dx.doi.org/10.1016/j.funbio.2018.09.001DOI Listing
November 2018

The soil-borne legacy in the age of the holobiont.

Microb Biotechnol 2019 01 16;12(1):51-54. Epub 2018 Oct 16.

Wheat Health, Genetics, and Quality Research Unit, United States Department of Agriculture, Agricultural Research Service, Pullman, WA, 99164-6430, USA.

Future efforts to increase agricultural productivity will focus on crops as functional units comprised of plants and their associated microflora in the context of the various environments in which they are grown. It is suggested that future efforts to increase agricultural productivity will focus on crops as functional units comprised of plants and their associated beneficial microorganisms in the context in which they are grown. Scientists, industry, and farmers must work closely together to develop, adapt, and apply new technologies to a wide range of cropping systems. Consumer education is needed help grow public awareness that 'plant probiotics' offer a safe and environmentally friendly alternative to dependence on the use of chemical pesticides.
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http://dx.doi.org/10.1111/1751-7915.13325DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6302707PMC
January 2019

Rapidly mitigating antibiotic resistant risks in chicken manure by Hermetia illucens bioconversion with intestinal microflora.

Environ Microbiol 2018 11;20(11):4051-4062

State Key Laboratory of Agricultural Microbiology, National Engineering Research Centre of Microbial Pesticides, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, China.

Antibiotic resistance genes (ARGs) in animal manure are an environmental concern due to naturally occurring bacteria being exposed to these wastes and developing multidrug resistance. The bioconversion of manure with fly larvae is a promising alternative for recycling these wastes while attenuating ARGs. We investigated the impact of black soldier fly (BSF, Hermetia illucens) larval bioconversion of chicken manure on the persistence of associated ARGs. Compared with traditional composting or sterile larval treatments (by 48.4% or 88.7%), non-sterile BSF larval treatments effectively reduced ARGs and integrin genes by 95.0% during 12 days, due to rapid decreases in concentrations of the genes and associated bacteria as they passed through the larval gut and were affected by intestinal microbes. After larval treatments, bacterial community composition differed significantly, with the percentage of Firmicutes possibly carrying ARGs reduced by 65.5% or more. On average, human pathogenic bacteria populations declined by 70.7%-92.9%, effectively mitigating risks of these bacteria carrying ARGs. Environmental pH, nitrogen content and antibiotic concentrations were closely related to both bacterial community composition and targeted gene attenuation in larval systems. Selective pressures of larval gut environments with intestinal microbes, larval bacteriostasis and reformulation of manure due to larval digestion contributed to ARG attenuation.
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http://dx.doi.org/10.1111/1462-2920.14450DOI Listing
November 2018

Differential Response of Wheat Cultivars to Pseudomonas brassicacearum and Take-All Decline Soil.

Phytopathology 2018 Dec 17;108(12):1363-1372. Epub 2018 Oct 17.

First author: State Key Laboratory of Crop Stress Biology for Arid Areas, College of Agronomy, Northwest A&F University, Yangling 712100, P.R. China; second author: Department of Cell and Molecular Biology, The University of Southern Mississippi, Hattiesburg 39406: and third and fourth authors: U.S. Department of Agriculture, Agricultural Research Service, Wheat Health, Genetics and Quality Research Unit, Pullman, WA 99164-6430.

2,4-Diacetylphloroglucinol (DAPG)-producing Pseudomonas spp. in the P. fluorescens complex are primarily responsible for a natural suppression of take-all of wheat known as take-all decline (TAD) in many fields in the United States. P. brassicacearum, the most common DAPG producer found in TAD soils in the Pacific Northwest (PNW) of the United States, has biological control, growth promoting and phytotoxic activities. In this study, we explored how the wheat cultivar affects the level of take-all suppression when grown in a TAD soil, and how cultivars respond to colonization by P. brassicacearum. Three cultivars (Tara, Finley, and Buchanan) supported similar rhizosphere population sizes of P. brassicacearum when grown in a TAD soil, however they developed significantly different amounts of take-all. Cultivars Tara and Buchanan developed the least and most take-all, respectively, and Finley showed an intermediate amount of disease. However, when grown in TAD soil that was pasteurized to eliminate both DAPG producers and take-all suppression, all three cultivars were equally susceptible to take-all. The three cultivars also responded differently to the colonization and phytotoxicity of P. brassicacearum strains Q8r1-96 and L5.1-96, which are characteristic of DAPG producers in PNW TAD soils. Compared with cultivar Tara, cultivar Buchanan showed significantly reduced seedling emergence and root growth when colonized by P. brassicacearum, and the response of Finley was intermediate. However, all cultivars emerged equally when treated with a DAPG-deficient mutant of Q8r1-96. Our results indicate that wheat cultivars grown in a TAD soil modulate both the robustness of take-all suppression and the potential phytotoxicity of the antibiotic DAPG.
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http://dx.doi.org/10.1094/PHYTO-01-18-0024-RDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6483097PMC
December 2018

Phenazine-1-carboxylic acid and soil moisture influence biofilm development and turnover of rhizobacterial biomass on wheat root surfaces.

Environ Microbiol 2018 06 26;20(6):2178-2194. Epub 2018 Jul 26.

United States Department of Agriculture - Agricultural Research Service, Wheat Health, Genetics, and Quality Research Unit, Pullman, WA 99164-6430, USA.

Phenazine-1-carboxylic acid (PCA) is produced by rhizobacteria in dryland but not in irrigated wheat fields of the Pacific Northwest, USA. PCA promotes biofilm development in bacterial cultures and bacterial colonization of wheat rhizospheres. However, its impact upon biofilm development has not been demonstrated in the rhizosphere, where biofilms influence terrestrial carbon and nitrogen cycles with ramifications for crop and soil health. Furthermore, the relationships between soil moisture and the rates of PCA biosynthesis and degradation have not been established. In this study, expression of PCA biosynthesis genes was upregulated relative to background transcription, and persistence of PCA was slightly decreased in dryland relative to irrigated wheat rhizospheres. Biofilms in dryland rhizospheres inoculated with the PCA-producing (PCA ) strain Pseudomonas synxantha 2-79RN were more robust than those in rhizospheres inoculated with an isogenic PCA-deficient (PCA ) mutant strain. This trend was reversed in irrigated rhizospheres. In dryland PCA rhizospheres, the turnover of N-labelled rhizobacterial biomass was slower than in the PCA and irrigated PCA treatments, and incorporation of bacterial N into root cell walls was observed in multiple treatments. These results indicate that PCA promotes biofilm development in dryland rhizospheres, and likely influences crop nutrition and soil health in dryland wheat fields.
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http://dx.doi.org/10.1111/1462-2920.14244DOI Listing
June 2018

Long-Term Irrigation Affects the Dynamics and Activity of the Wheat Rhizosphere Microbiome.

Front Plant Sci 2018 21;9:345. Epub 2018 Mar 21.

Wheat Health, Genetics and Quality Research Unit, USDA Agricultural Research Service, Pullman, WA, United States.

The Inland Pacific Northwest (IPNW) encompasses 1. 6 million cropland hectares and is a major wheat-producing area in the western United States. The climate throughout the region is semi-arid, making the availability of water a significant challenge for IPNW agriculture. Much attention has been given to uncovering the effects of water stress on the physiology of wheat and the dynamics of its soilborne diseases. In contrast, the impact of soil moisture on the establishment and activity of microbial communities in the rhizosphere of dryland wheat remains poorly understood. We addressed this gap by conducting a three-year field study involving wheat grown in adjacent irrigated and dryland (rainfed) plots established in Lind, Washington State. We used deep amplicon sequencing of the V4 region of the 16S rRNA to characterize the responses of the wheat rhizosphere microbiome to overhead irrigation. We also characterized the population dynamics and activity of indigenous Phz rhizobacteria that produce the antibiotic phenazine-1-carboxylic acid (PCA) and contribute to the natural suppression of soilborne pathogens of wheat. Results of the study revealed that irrigation affected the Phz rhizobacteria adversely, which was evident from the significantly reduced plant colonization frequency, population size and levels of PCA in the field. The observed differences between irrigated and dryland plots were reproducible and amplified over the course of the study, thus identifying soil moisture as a critical abiotic factor that influences the dynamics, and activity of indigenous Phz communities. The three seasons of irrigation had a slight effect on the overall diversity within the rhizosphere microbiome but led to significant differences in the relative abundances of specific OTUs. In particular, irrigation differentially affected multiple groups of and , including taxa with known plant growth-promoting activity. Analysis of environmental variables revealed that the separation between irrigated and dryland treatments was due to changes in the water potential (Ψ) and pH. In contrast, the temporal changes in the composition of the rhizosphere microbiome correlated with temperature and precipitation. In summary, our long-term study provides insights into how the availability of water in a semi-arid agroecosystem shapes the belowground wheat microbiome.
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http://dx.doi.org/10.3389/fpls.2018.00345DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5871930PMC
March 2018

Multiple Modes of Nematode Control by Volatiles of 1A00316 from Antarctic Soil against .

Front Microbiol 2018 23;9:253. Epub 2018 Feb 23.

State Key Laboratory of Agricultural Microbiology and National Engineering Research Center of Microbe Pesticides, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, China.

1A00316 isolated from Antarctic soil showed nematicidal potential for biological control of ; however, little was known about whether strain 1A00316 could produce volatile organic compounds (VOCs), and if they had potential for use in biological control against . In this study, VOCs produced by a culture filtrate of 1A00316 were evaluated by experiments in three-compartment Petri dishes and 96-well culture plates. Our results showed that juveniles gradually reduced their movement within 24-48 h of incubation with mortality ranging from 6.49 to 86.19%, and mostly stopped action after 72 h. Moreover, egg hatching in culture filtrates of strain 1A00316 was much reduced compared to that in sterile distilled water or culture medium. Volatiles from 1A00316 analysis carried out by solid-phase micro-extraction gas chromatography-mass spectrometry (SPME-GC/MS) included dimethyl-disulfide, 1-undecene, 2-nonanone, 2-octanone, (Z)-hexen-1-ol acetate, 2-undecanone, and 1-(ethenyloxy)-octadecane. Of these, dimethyl-disulfide, 2-nonanone, 2-octanone, (Z)-hexen-1-ol acetate, and 2-undecanone had strong nematicidal activity against J2 larvae by direct-contact in 96-well culture plates, and only 2-undecanone acted as a fumigant. In addition, the seven VOCs inhibited egg hatching of both by direct-contact and by fumigation. All of the seven VOCs repelled J2 juveniles in 2% water agar Petri plates. These results show that VOCs from strain 1A00316 act on different stages in the development of via nematicidal, fumigant, and repellent activities and have potential for development as agents with multiple modes of control of root-knot nematodes.
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http://dx.doi.org/10.3389/fmicb.2018.00253DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5863520PMC
February 2018

Volatile organic compounds from Paenibacillus polymyxa KM2501-1 control Meloidogyne incognita by multiple strategies.

Sci Rep 2017 11 24;7(1):16213. Epub 2017 Nov 24.

State Key Laboratory of Agricultural Microbiology and National Engineering Research Center of Microbial Pesticides, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, 430070, Hubei, China.

Plant-parasitic nematodes (PPNs) cause serious crop losses worldwide. In this study, we investigated the nematicidal factors and the modes and mechanisms of action involved in nematode control by Paenibacillus polymyxa KM2501-1. Treatment of the second-stage juveniles (J2) juveniles of PPN Meloidogyne incognita with the biological control agent KM2501-1 resulted in a mortality of 87.66% in vitro and reduced symptoms on tomato by up to 82.61% under greenhouse conditions. We isolated 11 volatile organic compounds (VOCs) from strain KM2501-1, of which 8 had contact nematicidal activity, 6 had fumigant activity, and 5 acted as stable chemotactic agents to M. incognita. The VOCs provided a comprehensive strategy against PPNs that included "honey-trap", fumigant, attractant and repellent modes. Furfural acetone and 2-decanol functioned as "honey-traps" attracting M. incognita and then killing it by contact or fumigation. Two other VOCs, 2-nonanone and 2-decanone, as well as strain KM2501-1 itself, destroyed the integrity of the intestine and pharynx. Collectively our results indicate that VOCs produced by P. polymyxa KM2501-1 act through diverse mechanisms to control M. incognita. Moreover, the novel "honey-trap" mode of VOC-nematode interaction revealed in this study extends our understanding of the strategies exploited by nematicidal biocontrol agents.
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http://dx.doi.org/10.1038/s41598-017-16631-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5701253PMC
November 2017

Sensitivity of Rhizoctonia Isolates to Phenazine-1-Carboxylic Acid and Biological Control by Phenazine-Producing Pseudomonas spp.

Phytopathology 2017 06 4;107(6):692-703. Epub 2017 Apr 4.

First and second authors: Department of Plant Pathology, Washington State University, Pullman 99164-6430; and third, fourth, and fifth authors: United States Department of Agriculture-Agricultural Research Service, Wheat Health, Genetics and Quality Research Unit, Pullman, WA 99164-6430.

Rhizoctonia solani anastomosis groups (AG)-8 and AG-2-1 and R. oryzae are ubiquitous in cereal-based cropping systems of the Columbia Plateau of the Inland Pacific Northwest and commonly infect wheat. AG-8 and R. oryzae, causal agents of Rhizoctonia root rot and bare patch, are most commonly found in fields in the low-precipitation zone, whereas R. solani AG-2-1 is much less virulent on wheat and is distributed in fields throughout the low-, intermediate-, and high-precipitation zones. Fluorescent Pseudomonas spp. that produce the antibiotic phenazine-1-carboxylic acid (PCA) also are abundant in the rhizosphere of crops grown in the low-precipitation zone but their broader geographic distribution and effect on populations of Rhizoctonia is unknown. To address these questions, we surveyed the distribution of PCA producers (Phz) in 59 fields in cereal-based cropping systems throughout the Columbia Plateau. Phz Pseudomonas spp. were detected in 37 of 59 samples and comprised from 0 to 12.5% of the total culturable heterotrophic aerobic rhizosphere bacteria. The frequency with which individual plants were colonized by Phz pseudomonads ranged from 0 to 100%. High and moderate colonization frequencies of Phz pseudomonads were associated with roots from fields located in the driest areas whereas only moderate and low colonization frequencies were associated with crops where higher annual precipitation occurs. Thus, the geographic distribution of Phz pseudomonads overlaps closely with the distribution of R. solani AG-8 but not with that of R. oryzae or R. solani AG-2-1. Moreover, linear regression analysis demonstrated a highly significant inverse relationship between annual precipitation and the frequency of rhizospheres colonized by Phz pseudomonads. Phz pseudomonads representative of the four major indigenous species (P. aridus, P. cerealis, P. orientalis, and P. synxantha) suppressed Rhizoctonia root rot of wheat when applied as seed treatments. In vitro, mean 50% effective dose values for isolates of AG-8 and AG-2-1 from fields with high and low frequencies of phenazine producers did not differ significantly, nor was there a correlation between virulence of an isolate and sensitivity to PCA, resulting in rejection of the hypothesis that tolerance in Rhizoctonia spp. to PCA develops in nature upon exposure to Phz pseudomonads.
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http://dx.doi.org/10.1094/PHYTO-07-16-0257-RDOI Listing
June 2017

Induced systemic resistance: a delicate balance.

Environ Microbiol Rep 2016 10;8(5):560-563

USDA-ARS Wheat Health, Genetics and Quality Research Unit, 365 Johnson Hall, Washington State University, Pullman, Washington, 99164-6430, USA.

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http://dx.doi.org/10.1111/1758-2229.12474DOI Listing
October 2016

Rhizosphere Competence of Wild-Type and Genetically Engineered Pseudomonas brassicacearum Is Affected by the Crop Species.

Phytopathology 2016 Jun 29;106(6):554-61. Epub 2016 Apr 29.

First author: Department of Crop and Soil Sciences, Washington State University, Pullman 99164-6420; and second and third authors: U.S. Department of Agriculture, Agricultural Research Service, Wheat Health, Genetics and Quality Research Unit, Pullman, WA 99164-6430.

2,4-Diacetylphloroglucinol (2,4-DAPG)-producing Pseudomonas brassicacearum Q8r1-96 is a highly effective biocontrol agent of take-all disease of wheat. Strain Z30-97, a recombinant derivative of Q8r1-96 containing the phzABCDEFG operon from P. synxantha (formerly P. fluorescens) 2-79 inserted into its chromosome, also produces phenazine-1-carboxylic acid. Rhizosphere population sizes of Q8r1-96, Z30-97, and 2-79, introduced into the soil, were assayed during successive growth cycles of barley, navy bean, or pea under controlled conditions as a measure of the impact of crop species on rhizosphere colonization of each strain. In the barley rhizosphere, Z30-96 colonized less that Q8r1-96 when they were introduced separately, and Q8r1-96 out-competed Z30-96 when the strains were introduced together. In the navy bean rhizosphere, Q8r1-96 colonized better than Z30-97 when the strains were introduced separately. However, both strains had similar population densities when introduced together. Strain Q8r1-96 and Z30-97 colonized the pea rhizosphere equally well when each strain was introduced separately, but Z30-97 out-competed Q8r1-96 when they were introduced together. To our knowledge, this is the first report of a recombinant biocontrol strain of Pseudomonas spp. gaining rhizosphere competitiveness on a crop species. When assessing the potential fate of and risk posed by a recombinant Pseudomonas sp. in soil, both the identity of the introduced genes and the crop species colonized by the recombinant strain need to be considered.
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http://dx.doi.org/10.1094/PHYTO-09-15-0244-RDOI Listing
June 2016

Molecular Characterization, Morphological Characteristics, Virulence, and Geographic Distribution of Rhizoctonia spp. in Washington State.

Phytopathology 2016 May 21;106(5):459-73. Epub 2016 Mar 21.

First and third authors: Department of Plant Pathology, Washington State University, Pullman, WA 99164-6430; and second, fourth, and fifth authors: U.S. Department of Agriculture-Agricultural Research Service, Wheat Health, Genetics and Quality Research Unit, Pullman, WA 99164-6430.

Rhizoctonia root rot and bare patch, caused by Rhizoctonia solani anastomosis group (AG)-8 and R. oryzae, are chronic and important yield-limiting diseases of wheat and barley in the Inland Pacific Northwest (PNW) of the United States. Major gaps remain in our understanding of the epidemiology of these diseases, in part because multiple Rhizoctonia AGs and species can be isolated from the same cereal roots from the field, contributing to the challenge of identifying the causal agents correctly. In this study, a collection totaling 498 isolates of Rhizoctonia was assembled from surveys conducted from 2000 to 2009, 2010, and 2011 over a wide range of cereal production fields throughout Washington State in the PNW. To determine the identity of the isolates, PCR with AG- or species-specific primers and/or DNA sequence analysis of the internal transcribed spacers was performed. R. solani AG-2-1, AG-8, AG-10, AG-3, AG-4, and AG-11 comprised 157 (32%), 70 (14%), 21 (4%), 20 (4%), 1 (0.2%), and 1 (0.2%), respectively, of the total isolates. AG-I-like binucleate Rhizoctonia sp. comprised 44 (9%) of the total; and 53 (11%), 80 (16%), and 51 (10%) were identified as R. oryzae genotypes I, II, and III, respectively. Isolates of AG-2-1, the dominant Rhizoctonia, occurred in all six agronomic zones defined by annual precipitation and temperature within the region sampled. Isolates of AG-8 also were cosmopolitan in their distribution but the frequency of isolation varied among years, and they were most abundant in zones of low and moderate precipitation. R. oryzae was cosmopolitan, and collectively the three genotypes comprised 37% of the isolates. Only isolates of R. solani AG-8 and R. oryzae genotypes II and III (but not genotype I) caused symptoms typically associated with Rhizoctonia root rot and bare patch of wheat. Isolates of AG-2-1 caused only mild root rot and AG-I-like binucleate isolates and members of groups AG-3, AG-4, and AG-11 showed only slight or no discoloration of the roots. However, all isolates of AG-2-1 caused severe damping-off of canola, resulting in 100% mortality. Isolates of Rhizoctonia AG-8, AG-2-1, AG-10, AG-I-like binucleate Rhizoctonia, and R. oryzae genotypes I, II, and III could be distinguished by colony morphology on potato dextrose agar, by PCR with specific primers, or by the type and severity of disease on wheat and canola seedlings, and results of these approaches correlated completely. Based on cultured isolates, we also identified the geographic distribution of all of these Rhizoctonia isolates in cereal-based production systems throughout Washington State.
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http://dx.doi.org/10.1094/PHYTO-09-15-0208-RDOI Listing
May 2016

Microbial and biochemical basis of a Fusarium wilt-suppressive soil.

ISME J 2016 Jan 9;10(1):119-29. Epub 2015 Jun 9.

IALS and Department of Plant Medicine, Gyeongsang National University, Jinju, Republic of Korea.

Crops lack genetic resistance to most necrotrophic pathogens. To compensate for this disadvantage, plants recruit antagonistic members of the soil microbiome to defend their roots against pathogens and other pests. The best examples of this microbially based defense of roots are observed in disease-suppressive soils in which suppressiveness is induced by continuously growing crops that are susceptible to a pathogen, but the molecular basis of most is poorly understood. Here we report the microbial characterization of a Korean soil with specific suppressiveness to Fusarium wilt of strawberry. In this soil, an attack on strawberry roots by Fusarium oxysporum results in a response by microbial defenders, of which members of the Actinobacteria appear to have a key role. We also identify Streptomyces genes responsible for the ribosomal synthesis of a novel heat-stable antifungal thiopeptide antibiotic inhibitory to F. oxysporum and the antibiotic's mode of action against fungal cell wall biosynthesis. Both classical- and community-oriented approaches were required to dissect this suppressive soil from the field to the molecular level, and the results highlight the role of natural antibiotics as weapons in the microbial warfare in the rhizosphere that is integral to plant health, vigor and development.
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http://dx.doi.org/10.1038/ismej.2015.95DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4681868PMC
January 2016

Draft Genome Sequence of the Phenazine-Producing Pseudomonas fluorescens Strain 2-79.

Genome Announc 2015 Mar 26;3(2). Epub 2015 Mar 26.

Department of Molecular Microbiology and Genetics, Institute of Microbiology and Genetics, Georg-August Universität, Göttingen, Germany

Pseudomonas fluorescens strain 2-79, a natural isolate of the rhizosphere of wheat (Triticum aestivum L.), possesses antagonistic potential toward several fungal pathogens. We report the draft genome sequence of strain 2-79, which comprises 5,674 protein-coding sequences.
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http://dx.doi.org/10.1128/genomeA.00130-15DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4384134PMC
March 2015

Biocontrol and plant growth-promoting activity of rhizobacteria from Chinese fields with contaminated soils.

Microb Biotechnol 2015 May 15;8(3):404-18. Epub 2014 Sep 15.

State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, China; Department of Plant Pathology, Washington State University, Pullman, WA, 99164-6430, USA.

The aim of this study was to inventory the types of plant growth-promoting rhizobacteria (PGPR) present in the rhizosphere of plants grown in soils contaminated with heavy metals, recalcitrant organics, petroleum sewage or salinity in China. We screened 1223 isolates for antifungal activity and about 24% inhibited Rhizoctonia solani or Sclerotinia sclerotiorum. Twenty-four strains inhibitory to R. solani, Gaeumannomyces graminis var. tritici and/or S. sclerotiorum and representing the dominant morphotypes were assayed for PGPR activity. Seven strains contained phlD, prnD, pltC or phzF genes and produced the antibiotics 2,4-diacetylphloroglucinol, pyrrolnitrin, pyoluteorin and phenazines respectively. Six strains contained acdS, which encodes 1-aminocyclopropane-1-carboxylic acid deaminase. Phylogenetic analysis of 16S rDNA and phlD, phzF and acdS genes demonstrated that some strains identified as Pseudomonas were similar to model PGPR strains Pseudomonas protegens Pf-5, Pseudomonas chlororaphis subsp. aureofaciens 30-84 and P. brassicacearum Q8r1-96. Pseudomonas protegens- and P. chlororaphis-like strains had the greatest biocontrol activity against Rhizoctonia root rot and take-all of wheat. Pseudomonas protegens and P. brassicacearum-like strains showed the greatest promotion of canola growth. Our results indicate that strains from contaminated soils are similar to well-described PGPR found in agricultural soils worldwide.
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http://dx.doi.org/10.1111/1751-7915.12158DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4408174PMC
May 2015

Pseudomonas protegens Pf-5 causes discoloration and pitting of mushroom caps due to the production of antifungal metabolites.

Mol Plant Microbe Interact 2014 Jul;27(7):733-46

Bacteria in the diverse Pseudomonas fluorescens group include rhizosphere inhabitants known for their antifungal metabolite production and biological control of plant disease, such as Pseudomonas protegens Pf-5, and mushroom pathogens, such as Pseudomonas tolaasii. Here, we report that strain Pf-5 causes brown, sunken lesions on peeled caps of the button mushroom (Agaricus bisporus) that resemble brown blotch symptoms caused by P. tolaasii. Strain Pf-5 produces six known antifungal metabolites under the control of the GacS/GacA signal transduction system. A gacA mutant produces none of these metabolites and did not cause lesions on mushroom caps. Mutants deficient in the biosynthesis of the antifungal metabolites 2,4-diacetylphloroglucinol and pyoluteorin caused less-severe symptoms than wild-type Pf-5 on peeled mushroom caps, whereas mutants deficient in the production of lipopeptide orfamide A caused similar symptoms to wild-type Pf-5. Purified pyoluteorin and 2,4-diacetylphloroglucinol mimicked the symptoms caused by Pf-5. Both compounds were isolated from mushroom tissue inoculated with Pf-5, providing direct evidence for their in situ production by the bacterium. Although the lipopeptide tolaasin is responsible for brown blotch of mushroom caused by P. tolaasii, P. protegens Pf-5 caused brown blotch-like symptoms on peeled mushroom caps through a lipopeptide-independent mechanism involving the production of 2,4-diacetylphloroglucinol and pyoluteorin.
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http://dx.doi.org/10.1094/MPMI-10-13-0311-RDOI Listing
July 2014

Biological control of wheat root diseases by the CLP-producing strain Pseudomonas fluorescens HC1-07.

Phytopathology 2014 Mar;104(3):248-56

Pseudomonas fluorescens HC1-07, previously isolated from the phyllosphere of wheat grown in Hebei province, China, suppresses the soilborne disease of wheat take-all, caused by Gaeumannomyces graminis var. tritici. We report here that strain HC1-07 also suppresses Rhizoctonia root rot of wheat caused by Rhizoctonia solani AG-8. Strain HC1-07 produced a cyclic lipopeptide (CLP) with a molecular weight of 1,126.42 based on analysis by electrospray ionization mass spectrometry. Extracted CLP inhibited the growth of G. graminis var. tritici and R. solani in vitro. To determine the role of this CLP in biological control, plasposon mutagenesis was used to generate two nonproducing mutants, HC1-07viscB and HC1-07prtR2. Analysis of regions flanking plasposon insertions in HC1-07prtR2 and HC1-07viscB revealed that the inactivated genes were similar to prtR and viscB, respectively, of the well-described biocontrol strain P. fluorescens SBW25 that produces the CLP viscosin. Both genes in HC1-07 were required for the production of the viscosin-like CLP. The two mutants were less inhibitory to G. graminis var. tritici and R. solani in vitro and reduced in ability to suppress take-all. HC1-07viscB but not HC-07prtR2 was reduced in ability to suppress Rhizoctonia root rot. In addition to CLP production, prtR also played a role in protease production.
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http://dx.doi.org/10.1094/PHYTO-05-13-0142-RDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5523110PMC
March 2014

Trapped intermediates in crystals of the FMN-dependent oxidase PhzG provide insight into the final steps of phenazine biosynthesis.

Acta Crystallogr D Biol Crystallogr 2013 Aug 13;69(Pt 8):1403-13. Epub 2013 Jul 13.

Lehrstuhl für Biochemie, Universität Bayreuth, Universitätsstrasse 30, 95447 Bayreuth, Germany.

Phenazines are redox-active secondary metabolites that many bacteria produce and secrete into the environment. They are broad-specificity antibiotics, but also act as virulence and survival factors in infectious diseases. Phenazines are derived from chorismic acid, but important details of their biosynthesis are still unclear. For example, three two-electron oxidations seem to be necessary in the final steps of the pathway, while only one oxidase, the FMN-dependent PhzG, is conserved in the phenazine-biosynthesis phz operon. Here, crystal structures of PhzG from Pseudomonas fluorescens 2-79 and from Burkholderia lata 383 in complex with excess FMN and with the phenazine-biosynthesis intermediates hexahydrophenazine-1,6-dicarboxylate and tetrahydrophenazine-1-carboxylate generated in situ are reported. Corroborated with biochemical data, these complexes demonstrate that PhzG is the terminal enzyme in phenazine biosynthesis and that its relaxed substrate specificity lets it participate in the generation of both phenazine-1,6-dicarboxylic acid (PDC) and phenazine-1-carboxylic acid (PCA). This suggests that competition between flavin-dependent oxidations through PhzG and spontaneous oxidative decarboxylations determines the ratio of PDC, PCA and unsubstituted phenazine as the products of phenazine biosynthesis. Further, the results indicate that PhzG synthesizes phenazines in their reduced form. These reduced molecules, and not the fully aromatized derivatives, are the likely end products in vivo, explaining why only one oxidase is required in the phenazine-biosynthesis pathway.
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http://dx.doi.org/10.1107/S0907444913008354DOI Listing
August 2013

pA506, a conjugative plasmid of the plant epiphyte Pseudomonas fluorescens A506.

Appl Environ Microbiol 2013 Sep 28;79(17):5272-82. Epub 2013 Jun 28.

Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon, USA.

Conjugative plasmids are known to facilitate the acquisition and dispersal of genes contributing to the fitness of Pseudomonas spp. Here, we report the characterization of pA506, the 57-kb conjugative plasmid of Pseudomonas fluorescens A506, a plant epiphyte used in the United States for the biological control of fire blight disease of pear and apple. Twenty-nine of the 67 open reading frames (ORFs) of pA506 have putative functions in conjugation, including a type IV secretion system related to that of MOBP6 family plasmids and a gene cluster for type IV pili. We demonstrate that pA506 is self-transmissible via conjugation between A506 and strains of Pseudomonas spp. or the Enterobacteriaceae. The origin of vegetative replication (oriV) of pA506 is typical of those in pPT23A family plasmids, which are present in many pathovars of Pseudomonas syringae, but pA506 lacks repA, a defining locus for pPT23A plasmids, and has a novel partitioning region. We selected a plasmid-cured derivative of A506 and compared it to the wild type to identify plasmid-encoded phenotypes. pA506 conferred UV resistance, presumably due to the plasmid-borne rulAB genes, but did not influence epiphytic fitness of A506 on pear or apple blossoms in the field. pA506 does not appear to confer resistance to antibiotics or other toxic elements. Based on the conjugative nature of pA506 and the large number of its genes that are shared with plasmids from diverse groups of environmental bacteria, the plasmid is likely to serve as a vehicle for genetic exchange between A506 and its coinhabitants on plant surfaces.
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http://dx.doi.org/10.1128/AEM.01354-13DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3753976PMC
September 2013