Negative cross-communication among wheat rhizosphere bacteria: effect on antibiotic production by the biological control bacterium Pseudomonas aureofaciens 30-84

• Published in: Applied and Environmental Microbiology Vol. 70; no. 5; pp. 3103 - 3109
• Main Authors: Morello, J.E, Pierson, E.A, Pierson, L.S. III
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.05.2004
• Subjects: Antibiotics; antifungal properties; Bacteria; Bacteria - growth & development; Bacteria - metabolism; Bacterial Proteins - metabolism; beta-galactosidase; Biological and medical sciences; biological control; biological control agents; biosynthesis; cell communication; Culture Media, Conditioned - pharmacology; Fundamental and applied biological sciences. Psychology; fungal antagonists; Gaeumannomyces graminis var. tritici; Gene expression; Gene Expression Regulation, Bacterial - drug effects; gene induction; in vitro studies; Microbiology; Pest Control, Biological; phenazines; Phenazines - metabolism; phzB gene; phzB promoter; Plant Diseases - microbiology; Plant Microbiology; plant pathogenic fungi; Plant Roots - microbiology; promoter regions; Pseudomonas - growth & development; Pseudomonas - metabolism; Pseudomonas aureofaciens; Pseudomonas chlororaphis; reporter genes; Signal Transduction; Soil Microbiology; Triticum - microbiology; Triticum aestivum; Wheat; Pseudomonadales; Monocotyledones; Biological control; Pseudomonas aureofaciens; Rhizosphere; Antibiotic; Gramineae; Angiospermae; Production; Pseudomonadaceae; Bacteria; Pseudomonas chlororaphis; Spermatophyta; Wheat; Triticum aestivum
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.70.5.3103-3109.2004

Phenazine antibiotic production in the biological control bacterium Pseudomonas aureofaciens 30-84 is regulated in part via the PhzR/PhzI N-acyl homoserine lactone (AHL) system. Previous work showed that a subpopulation of the wheat rhizosphere community positively affected phenazine gene expression in strain 30-84 via AHL signals (E. A. Pierson, D. W. Wood, J. A. Cannon, F. M. Blachere, and L. S. Pierson III, Mol. Plant-Microbe Interact. 11:1078-1084, 1998). In the present work, a second subpopulation, one that negatively affected phenazine gene expression, was identified from this rhizosphere community. Strain 30-84 grown in conditioned medium (CM) from several strains produced lower levels of phenazines (1.5- to 9.3-fold) than control when grown in CM from the strain 30-84I1/I2. Growth of the phzB::lacZ reporter strain 30-84Z in this CM resulted in decreased lacZ expression (4.3- to 9.2-fold) compared to growth of the control strain in CM, indicating that inhibition of phzB occurred at the level of gene expression. Preliminary chemical and biological characterizations suggested that these signals, unlike other identified negative signals, were not extractable in ethyl acetate. Introduction of extra copies of phzR and phzI, but not phzI alone, in trans into strain 30-84Z reduced the negative effect on phzB::lacZ expression. The presence of negative-signal-producing strains in a mixture with strain 30-84 reduced strain 30-84's ability to inhibit the take-all disease pathogen in vitro. Together, the results from the previous work on the positive-signal subpopulation and the present work on the negative-signal subpopulation suggest that cross-communication among members of the rhizosphere community and strain 30-84 may control secondary metabolite production and pathogen inhibition.