Regulation of polar flagellum genes is mediated by quorum sensing and FlhDC in Burkholderia glumae

• Published in: Molecular microbiology Vol. 64; no. 1; pp. 165 - 179
• Main Authors: Kim, Jinwoo, Kang, Yongsung, Choi, Okhee, Jeong, Yeonhwa, Jeong, Jae-Eun, Lim, Jae Yun, Kim, Minkyun, Moon, Jae Sun, Suga, Hiroaki, Hwang, Ingyu
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01-04-2007; Blackwell Publishing Ltd; Blackwell Science
• Subjects: Amino Acid Sequence; Anatomy & physiology; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Base Sequence; Binding sites; Biochemistry; Biological and medical sciences; Burkholderia - growth & development; Burkholderia - metabolism; Burkholderia - pathogenicity; Burkholderia - physiology; Chemical compounds; Chemotaxis; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Flagella - genetics; Flagella - metabolism; Fundamental and applied biological sciences. Psychology; Gene expression; Gene Expression Regulation, Bacterial; Genes; Microbiology; Miscellaneous; Molecular Sequence Data; Multigene Family; Mutation; Oryza - microbiology; Plant Diseases - microbiology; Plant pathology; Proteins; Quorum Sensing; Rice; Trans-Activators - genetics; Trans-Activators - metabolism; Plant pathogen; Gene; Microbiology; Burkholderia glumae; Flagellum; Bacteria; Quorum sensing
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/j.1365-2958.2007.05646.x

The bacterium Burkholderia glumae causes rice grain rot by producing toxoflavin, whose expression is regulated by quorum sensing (QS). We report a major deviation from the current paradigm for the regulation of bacterial polar flagellum genes. The N-octanoyl homoserine lactone (C8-HSL)-deficient mutant of B. glumae is aflagellate and has lost the ability to swim and swarm at 37°C. Mutagenesis of the bacterium with the mini-Tn5rescue identified an IclR-type transcriptional regulator, called QsmR, which is important for flagellum formation. TofR, which is a cognate C8-HSL receptor, activated qsmR expression by binding directly to the qsmR promoter region. From the flagellum gene cluster, we identified flhDC homologues that are directly activated by QsmR. FlhDC in turn activates the expression of genes involved in flagellum biosynthesis, motor functions and chemotaxis in B. glumae. Non-motile qsmR, fliA and flhDC mutants produced toxoflavin, but lost pathogenicity for rice. The unexpected discovery of FlhDC in a polarly flagellate bacterium suggests that exceptions to the typical regulatory mechanisms of flagellum genes exist in Gram-negative bacteria. The finding that functional flagella play critical roles in the pathogenicity of B. glumae suggests that either QS or flagellum formation constitutes a good target for the control of rice grain rot.