Quorum Sensing Controls Flagellar Morphogenesis in Burkholderia glumae

Abstract

Burkholderia glumae is a motile plant pathogenic bacterium that has multiple polar flagella and one LuxR/LuxI-type quorum sensing (QS) system, TofR/TofI. A QS-dependent transcriptional regulator, QsmR, activates flagellar master regulator flhDC genes. FlhDC subsequently activates flagellar gene expression in B. glumae at 37 degrees C. Here, we confirm that the interplay between QS and temperature is critical for normal polar flagellar morphogenesis in B. glumae. In the wild-type bacterium, flagellar gene expression and flagellar number were greater at 28 degrees C compared to 37 degrees C. The QS-dependent flhC gene was significantly expressed at 28 degrees C in two QS-defective (tofI::Omega and qsmR::Omega) mutants. Thus, flagella were present in both tofI::Omega and qsmR::Omega mutants at 28 degrees C, but were absent at 37 degrees C. Most tofI::Omega and qsmR::Omega mutant cells possessed polar or nonpolar flagella at 28 degrees C. Nonpolarly flagellated cells processing flagella around cell surface of both tofI::Omega and qsmR::Omega mutants exhibited tumbling and spinning movements. The flhF gene encoding GTPase involved in regulating the correct placement of flagella in other bacteria was expressed in QS mutants in a FlhDC-dependent manner at 28 degrees C. However, FlhF was mislocalized in QS mutants, and was associated with nonpolar flagellar formation in QS mutants at 28 degrees C. These results indicate that QS-independent expression of flagellar genes at 28 degrees C allows flagellar biogenesis, but is not sufficient for normal polar flagellar morphogenesis in B. glumae. Our findings demonstrate that QS functions together with temperature to control flagellar morphogenesis in B. glumae.