Leland S. Pierson, III. Associate Professor, Department of Plant Pathology. Ph.D., Washington State University. Microbial gene regulation in the rhizosphere; mechanisms involved in biological control of plant pathogens.

All living organisms need to obtain nutrients for survival, growth and reproduction. It is becoming clear that in the case of host-associated bacteria, nutrient procurement involves highly evolved recognition systems that utilize complex signaling pathways among and between the bacterium and its host. In the rhizosphere, the zone of soil in which microorganisms are subject to the influence of the plant root, competition for the increased nutrients available as root exudates is intense. In response to this competition, bacteria have evolved diverse mechanisms which enable them to effectively compete for these resources. In essence, biological control of most root pathogens is a consequence of competition between the introduced biocontrol strain and other microorganisms, including the pathogen. In order to understand, and ultimately to improve biological control, we must understand the role of the competitive mechanisms in the lifecycle of the bacterium and the molecular circuitry used to regulate their production. My laboratory is studying the regulation of phenazine antibiotic production in Pseudomonas aureofaciens strain 30-84. This bacterium colonizes plant roots and inhibits the growth of several fungal plant pathogens through the production of phenazine antibiotics. We have found that the expression of the genes responsible for phenazine production is exquisitely regulated at multiple levels. We have identified a sensory transduction pathway that includes the production of a diffusible signal molecule that allows intra-population and inter-population signaling to occur on the plant root. In addition, sensitive reporter fusions are being used to study the influence of the host, indigenous microflora, and the pathogen on bacterial gene expression on the root.

Pierson, L.S. III. Genetic analysis of selected antifungal metabolites produced by Pseudomonas aureofaciens. In: Plant-Microbe Interactions and Biological Control. Boland, G.J., and Kuykendall, L.D., eds. Marcel Dekker, Inc. (in press).

Wood, D.W., and Pierson, L.S. III. The phzI gene of Pseudomonas aureofaciens 30-84 is responsible for the production of a diffusible signal required for phenazine antibiotic production. Gene (in press).

Pierson, L.S. III, Gaffney, T., Lam, S., and Gong, F.C. Molecular analysis of genes encoding phenazine biosynthesis in the biological control bacterium Pseudomonas aureofaciens 30-84. FEMS Microbiology Letters (in press).

Pierson, L.S. III, Keppenne, V.D., and Wood, D.W. 1994. Phenazine antibiotic biosynthesis in Pseudomonas aureofaciens 30-84 is regulated by PhzR in response to cell density. J. Bacteriol. 176:3966-3974.

Pierson, L.S. III, and Pierson, E.A.. Phenazine antibiotic production by the biological control bacterium Pseudomonas aureofaciens: role in ecology and disease suppression. FEMS Microbiology Letters (in press).