Bacterial secondary metabolites mediate cooperative and competitive interactions between rhizosphere microorganisms
Q. YAN (1), B. Philmus (2), J. Chang (3), J. Loper (4) (1) Oregon State University, U.S.A.; (2) Oregon State University, U.S.A.; (3) Oregon State University, U.S.A.; (4) USDA-ARS Horticultural Crops Research Laboratory, U.S.A.

Bacteria are highly cooperative and competitive in their habitats on plant surfaces and secondary metabolites play a role in both processes. Pseudomonas protegens Pf-5 suppresses soilborne plant diseases due to the production of a large spectrum of antibiotics. Among the antibiotics produced by Pf-5, pyoluteorin (Plt) and 2,4-diacetylphloroglucinol (DAPG) are coordinately regulated and both function in intracellular and intercellular communication. We previously showed that phloroglucinol (PG), an intermediate of DAPG synthesized by PhlD, is required for production of both DAPG and Plt. This study focused on pltM, which encodes a putative halogenase required for Plt production.  Purified PltM transformed PG into chlorinated PGs (chloro-1,3,5-trihydroxybenzene and 2,4-dichlorobenzene-1,3,5-triol), which chemically complemented pltM and phlD mutants for Plt production and inhibition of Pythium ultimum. These chlorinated PGs were detected in cultures of Pf-5, but not in cultures of pltM or phlD mutants. A pltM mutant could produce Plt if co-cultured with a strain that produced a chlorinated PG. Our data demonstrate that PG, an intermediate in DAPG biosynthesis, is chlorinated by PltM into intercellular signals regulating Plt production. DAPG and Plt are potent antibiotics contributing to the suppression of plant diseases, and their biosynthetic genes also function jointly to synthesize metabolites serving as intercellular signals coordinating antibiotic production.

Abstract Number: P5-132
Session Type: Poster