Submitted to: Proceedings of Workshop on Global Int Org Biocontrol (IOBC) Working Group
Publication Type: Proceedings
Publication Acceptance Date: 9/1/2005
Publication Date: 1/20/2006
Citation: Mavrodi, O.V., Mavrodi, D.V., Weller, D.M., Thomashow, L.S. 2006. Role of ptsp recombinase and orft genes in root colonization by pseudomonas fluorescens q8r1-96. Proceedings of Workshop on Global Int Org Biocontrol (IOBC) Working Group. IOBC/WPRS Bulletin Vol. 29(2) The Netherlands. 2006 Interpretive Summary: Take-all decline (TAD) is a natural biological control of take-all disease of wheat caused by Gaeumannomyces graminis var. tritici. TAD develops because of the buildup of isolates of Pseudomonas fluorescens, which produce the antifungal compound 2,4-diacetylphloroglucinol (DAPG). Because DAPG-producing strains are such aggressive colonists of wheat roots, they are a rich source of biocontrol agents that can be applied directly to seeds to suppress root pathogens. This studies reports on genes that were hypothesized to contribute to the unique colonizing abilities of DAPG-producing bacteria.
Technical Abstract: Q8r1-96 is representative of the D-genotype of DAPG producers, which aggressively colonize and maintain large population sizes on the roots of wheat, pea, and sugarbeet. In order to study the role of ptsP and orfT in colonization of the wheat rhizosphere, clones containing these genes were identified in a Q8r1-96 genomic library, sequenced, and used to construct gene replacement mutants of Q8r1-96. The ptsP and orfT genes influence global processes including organic nitrogen utilization and transmembrane transport, respectively. Mutants in these genes were characterized phenotypically for 2,4-DAPG production, motility, fluorescence, colony morphology, exoprotease and hydrogen cyanide production, carbon and nitrogen utilization, and the ability to colonize the rhizosphere of wheat grown in a natural soil. Colonies formed by the mutant orfT did not differ from those of Q8r1-96, whereas those of the ptsP mutant exhibited altered colony morphology, increased fluorescence, and decreased motility. In addition, the ptsP mutant produced decreased amounts of exoprotease and phloroglucinol compounds as compared to the wild type. The ptsP mutant was impaired in wheat root colonization, whereas the orfT mutant was not impaired. However, both mutants were less competitive than P. fluorescens Q8r1-96 in the wheat rhizosphere when introduced into the soil in mixed inoculation with the parental strain.