W727 Rhizobacterial Community Structure and Function in a Dryland Ecosystem

Date: Sunday, January 15, 2012
Time: 8:20 AM
Room: Pacific Salon 2
Linda S. Thomashow , Agricultural Research Service, US Department of Agriculture, Pullman, WA
D. V. Mavrodi , Department of Plant Pathology, Washington State University, Pullman, WA
O. V. Mavrodi , Department of Plant Pathology, Washington State University, Pullman, WA
R. F. Bonsall , Department of Plant Pathology, Washington State University, Pullman, WA
K. Breakwell , Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, Australia
J. A. Parejko , Molecular and Cellular Biology, Washington State University, Pullman, WA
D. A. Weller , Agricultural Research Service, US Department of Agriculture, Pullman, WA
I. T. Paulsen , Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, Australia
We recently discovered large populations of phenazine-producing (Phz+) Pseudomonas strains and concentrations of the antibiotic phenazine-1-carboxylic acid (PCA) of up to 1.6 µg g-1 of root plus rhizosphere soil on roots of non-irrigated cereals grown over more than a million hectares of the Columbia Plateau of central Washington State. To test the hypothesis that these Phz+ populations are enriched specifically under dryland conditions, we established adjacent irrigated and nonirrigated plots of wheat at the Washington State University Dryland Research Station at Lind, Washington in March of  2011. We monitored population densities and rhizosphere colonization frequencies of indigenous Phz+ bacteria, as well as rhizosphere concentrations of PCA, at two-week intervals until harvest four months later. With or without irrigation, Phz+ bacterial populations increased until mid-June, and then populations in the irrigated plots declined significantly as compared to those in the nonirrigated plots. We also recovered PCA from roots grown with or without irrigation until June, by which time amounts recovered under either condition had declined significantly as compared to amounts recovered earlier in the season. As a first step towards understanding the molecular mechanisms involved in survival of Phz+ bacteria under dryland conditions, we have begun to generate a draft sequence of P. fluorescens 2-79, a well-studied biocontrol strain isolated over 30 years ago from the Lind site. We also have isolated rhizosphere DNA three times during the field experiment in order to perform a global analysis of bacterial community structure in the rhizosphere of wheat grown under irrigated and dryland conditions. We expect results of these analyses to provide insight into the major phylogenetic groups represented in each community, reveal how each sample differs in terms of species diversity and composition, and enable us to determine whether these differences can be correlated with soil moisture and wheat growth stage.