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Differential regulatory systems of virulence-related functions between two strains of Burkholderia glumae require a common master regulator qsmR

Tiago De Paula Lelis: Louisiana State University

<div><em>Burkholderia glumae</em> is a major bacterial pathogen of rice in the United States. Significant phenotypic and genotypic variations have been reported within this specie. <em>B. glumae</em> strains 336gr-1 and 411gr-6 show phenotypic variations in virulence and pigmentation. Virulence-related genes are mostly regulated by the TofI/TofR-mediated quorum sensing (QS) system. To study the function of QS in <em>B. glumae</em> 336gr-1 and 411gr-6, a series of deletion mutants were generated for <em>ΔtofI/tofR</em> derivatives using the pkkSacB suicide vector. The <em>ΔtofI/tofR</em> derivative of 336gr-1 completely lost its ability to produce toxoflavin in LB media, and its extracellular protease activity in NA agar supplemented with 1% skim milk. However, the <em>ΔtofI/tofR</em> derivative of 411gr-6 retained the ability to produce toxoflavin, and extracellular protease in a lower level compared to its parent strain 411gr-6. Additionally, virulence of each quorum-sensing-defective derivatives was tested with the susceptible rice cultivar Trenasse. 336gr-1 ΔtofI/R and 411gr-6 ΔtofI/R exhibited retained virulence to cause disease in the rice plants with disease severity scoring as much as 20% and 60%, respectively, at 14 days after inoculation. Remarkably, it was found that deletion of <em>qsmR</em>, a regulatory gene for quorum-sensing, abolished toxoflavin production, and extracellular protease activity in both 336gr-1, and 411gr-6 strains, indicating the master regulatory role of this gene for the bacterial pathogenesis.</div>