Rhizobacterial community structure and function in dryland wheat
L. THOMASHOW (1), D. Mavrodi (2), O. Mavrodi (3), J. Parejko (4), M. Le Tourneau (5), R. Bonsall (3), D. Weller (1) (1) USDA-ARS, U.S.A.; (2) Department of Biological Sciences, The University of Southern Mississippi, U.S.A.; (3) Department of Plant Pathology, Washington State University, U.S.A.; (4) Department of Microbiology, University of Wisconsin-LaCrosse, U.S.A.; (5) Department of Soils, Washington State University, U.S.A.

Certain fluorescent Pseudomonas spp. produce phenazine antibiotics inhibitory to root pathogens. These rhizobacteria include P. synxantha 2-79 and representatives of at least three other Pseudomonas species that produce phenazine-1-carboxylic acid (PCA) and comprise up to 10% of the total culturable heterotrophic aerobic bacteria on the roots of dryland spring wheat grown in the inland Pacific Northwest, USA. PCA production on roots of field-grown wheat occurred mainly during the first half of the growing season but remained detectable for at least 130 days after planting. In vitro, the compound had a half-life of 3 or 4 days in dry or moist soils, respectively, and remained detectable throughout the 3-week experiment. These data indicate that most PCA synthesis in the field occurs early in the season, but that synthesis may continue to occur even as soil water potentials approach -400 to -500 kPa. We suggest that PCA producers (Phz+) survive desiccation on roots in biofilms. Comparisons of bacterial colony morphology on root samples by SEM and helium ion microscopy consistently showed more robust biofilms on roots colonized by wild-type strain 2-79 than on roots colonized by its Phz- mutant under dryland conditions.

Abstract Number: P3-81
Session Type: Poster