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The secret life of bacteria: The interaction of Enterobacter and the soil pathogen Rhizoctonia solani

Peiqi Zhang: University of Florida

<div>Bacteria and fungi in mycorhizosphere both have a profound impact on the health of crops. Various endohyphal bacteria have been isolated from the soil fungus <em>Rhizoctonia solani</em> AG2-2IIIB, which causes brown patch disease in cool season turfgrass, including the <em>Enterobacter</em> sp. strain named En-cren. Endophytic En-cren was shown to contribute to the virulence of the fungal pathogen and it can be released as a free-living bacterium when hyphae are damaged, rapidly migrating along the outside of hyphae. The objectives to this study was to identify the genetic nature of hyphal motility of the bacteria and whether the bacteria contribute to the virulence of the fungal pathogen through the production of phenylacetic acid (PAA). The bacteria can travel by the aerial hyphae of <em>R. solani</em> and presumably expand to new niches in the soil environment. Single mutations in flagella hook protein <em>flgE</em> and type IV pilus secretin <em>pilQ</em> did not prevent hyphal movement. The tests of double mutants of both motility apparatus are in progress. En-cren produces PAA and indole acetic acid (IAA), of which the former has been proposed as a virulence factor of <em>R. solani</em>. Mutation of the gene for indole pyruvate decarboxylase suppressed PAA and IAA production in free-living cultures of the bacterium. The study will provide greater understanding of the interaction of bacteria and fungi of the mycorhizosphere and, more specifically, of the broad range soil pathogen <em>Rhizoctonia solani</em>.</div>