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Regulation of toxin production by Rathayibacter toxicus, causative agent of bacterial head blight of grasses and annual ryegrass toxicity

Elizabeth Rogers: USDA ARS FDWSRU

<div>The USDA-APHIS select agent<em> Rathayibacter toxicus</em> is a gram-positive bacterium that produces a lethal tunicamycin-like toxin in many forage grasses in association with seed gall nematodes from <em>Anguina</em> and related genera. To date, <em>R. toxicus</em> has only been found in Australia; however, anguinid seed gall nematodes are widespread, including in the grass seed production areas of the U.S. Pacific Northwest. At this point, little is known about when or why <em>R. toxicus</em> produces tunicamycin. Whole genome sequencing has identified a putative tunicamycin biosynthetic gene cluster (TGC) which contains genes similar to all 12 essential genes necessary for tunicamycin production in the characterized TGC from <em>Streptomyces chartreusis.</em> Triggers of toxin production under field conditions are unknown, although tunicamycin concentration increases in the final stages of seed maturation and drying. In the laboratory, toxin production can be turned on using a bacteriophage (NCPPB 3778). However, <em>R. toxicus</em> rapidly stops producing tunicamycin under standard laboratory growth conditions. Preliminary qRT-PCR experiments have shown that the TGC is expressed constitutively under both toxin-producing and non-producing conditions, suggesting post-transcriptional regulation of tunicamycin biosynthesis. Results from ongoing experiments examining the transcription, translation, and protein function of the TGC will be presented.</div>