- Volume 160, Issue 10, 2014
Volume 160, Issue 10, 2014
- Physiology and Biochemistry
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Role of gliotoxin in the symbiotic and pathogenic interactions of Trichoderma virens
Using a gene disruption strategy, we generated mutants in the gliP locus of the plant-beneficial fungus Trichoderma virens that were no longer capable of producing gliotoxin. Phenotypic assays demonstrated that the gliP-disrupted mutants grew faster, were more sensitive to oxidative stress and exhibited a sparse colony edge compared with the WT strain. In a plate confrontation assay, the mutants deficient in gliotoxin production were ineffective as mycoparasites against the oomycete, Pythium ultimum, and the necrotrophic fungal pathogen, Sclerotinia sclerotiorum, but retained mycoparasitic ability against Rhizoctonia solani. Biocontrol assays in soil showed that the mutants were incapable of protecting cotton seedlings from attack by P. ultimum, against which the WT strain was highly effective. The mutants, however, were as effective as the WT strain in protecting cotton seedlings against R. solani. Loss of gliotoxin production also resulted in a reduced ability of the mutants to attack the sclerotia of S. sclerotiorum compared with the WT. The addition of exogenous gliotoxin to the sclerotia colonized by the mutants partially restored their degradative abilities. Interestingly, as in Aspergillus fumigatus, an opportunistic human pathogen, gliotoxin was found to be involved in pathogenicity of T. virens against larvae of the wax moth, Galleria mellonella. The loss of gliotoxin production in T. virens was restored by complementation with the gliP gene from A. fumigatus. We have, thus, demonstrated that the putative gliP cluster of T. virens is responsible for the biosynthesis of gliotoxin, and gliotoxin is involved in mycoparasitism and biocontrol properties of this plant-beneficial fungus.
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Functional characterization of the dguRABC locus for d-Glu and d-Gln utilization in Pseudomonas aeruginosa PAO1
More Lessd-Glu, an essential component of peptidoglycans, can be utilized as a carbon and nitrogen source by Pseudomonas aeruginosa. DNA microarrays were employed to identify genes involved in d-Glu catabolism. Through gene knockout and growth phenotype analysis, the divergent dguR–dguABC (d-Glu utilization) gene cluster was shown to participate in d-Glu and d-Gln catabolism and regulation. Growth of the dguR and dguA mutants was abolished completely on d-Glu or retarded on d-Gln as the sole source of carbon and/or nitrogen. The dguA gene encoded a FAD-dependent d-amino acid dehydrogenase with d-Glu as its preferred substrate, and its promoter was specifically induced by exogenous d-Glu and d-Gln. The function of DguR as a transcriptional activator of the dguABC operon was demonstrated by promoter activity measurements in vivo and by mobility shift assays with purified His-tagged DguR in vitro. Although the DNA-binding activity of DguR did not require d-Glu, the presence of d-Glu, but not d-Gln, in the binding reaction was found to stabilize a preferred nucleoprotein complex. The presence of a putative DguR operator was revealed by in silica analysis of the dguR–dguA intergenic regions among Pseudomonas spp. and binding of DguR to a highly conserved 19 bp sequence motif was further demonstrated. The dguB gene encodes a putative enamine/imine deaminase of the RidA family, but its role in d-Glu catabolism remains to be determined. Whilst a lesion in dguC encoding a periplasmic solute binding protein only affected growth on d-Glu slightly, expression of the previously characterized AatJMQP transporter for acidic l-amino acid uptake was found inducible by d-Glu and essential for d-Glu utilization. In summary, the findings of this study supported DguA as a new member of the FAD-dependent d-amino acid dehydrogenase family, and DguR as a d-Glu sensor and transcriptional activator of the dguA promoter.
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