Cross-Regulation in Vibrio parahaemolyticus : Compensatory Activation of Polar Flagellar Genes by the Lateral Flagellar Regulator LafK

Abstract

Gene organization and hierarchical regulation of the polar flagellar genes of Vibrio parahaemolyticus, Vibrio cholerae, and Pseudomonas aeruginosa appear highly similar, with one puzzling difference. Two 54 -dependent regulators are required to direct different classes of intermediate flagellar gene expression in V. cholerae and P. aeruginosa, whereas the V. parahaemolyticus homolog of one of these regulators, FlaK, appears dispensable. Here we demonstrate that there is compensatory activation of polar flagellar genes by the lateral flagellar regulator LafK.Acting as propellers driven by rotary motors, flagella are highly complex and efficient molecular machines. Flagellar assembly, which occurs via a flagellum-specific type three secretion system, initiates with the formation of a ring structure in the membrane. It proceeds to formation of a basal body hook and culminates with the polymerization of the extracytoplasmic propeller-like filament, subunits of which are secreted through the basal body hook structure (reviewed in reference 9). The assembly of this complex organelle requires the products of more than 35 genes. Flagellar gene expression is carefully regulated by a number of mechanisms such that there are sequential classes of gene expression coupled to morphogenesis of the organelle (reviewed in reference 1).Although the classes of temporally expressed flagellar genes are generally comparable (with a few variations), the specific regulators and sigma factors controlling early, middle, and late gene expression differ considerably. Flagellar gene organization and the specific transcriptional regulators of polar flagellar genes appear similar in many Vibrio and Pseudomonas species (reviewed in reference 14). In these organisms, 54 -dependent transcription factors regulate expression of intermediate genes, which encode components of the flagellar export-assembly complex and basal body hook structure. An alternate sigma factor ( 28 ) directs late polar gene expression, including transcription of propeller-encoding genes (e.g., flagellin genes). In Vibrio cholerae and Pseudomonas aeruginosa, experiments suggest that there are four classes in the temporal hierarchy of expression, with two subclasses of intermediate genes requiring There has been a puzzling discrepancy between observations of the phenotype of mutants of V. parahaemolyticus that is not in accordance with the regulatory scheme deciphered for other polarly flagellated Vibrio and Pseudomonas species. The flaK gene was discovered as an open reading frame encoding a potential 54 -dependent regulator located downstream of the flagellin chaperone-encoding gene fliS (formerly named flaJ). The gene was disrupted, but disappointingly it was not found to be important for swimming motility (21). Bacteria with flaK lesions have only slight swimming motility defects, an observation that is not consistent with FlaK being required for intermediate flagellar gene expression. Therefore, another regulatory scenario must be postulated for V. parahaemolyticus. In t...

Transcriptional Hierarchy of Aeromonas hydrophila Polar-Flagellum Genes

“…parahaemolyticus and some A. hydrophila strains express dual flagellum systems, and LafK is the lateral-flagellum master regulator (8,39). In V. parahaemolyticus LafK is able to compensate for the mutation of the polar-flagellum 54 -dependent response regulator FlaK (19). Data obtained are consistent with the fact that the A. hydrophila FlrA mutation abolishes polar-flagellum formation in liquid and solid media but does not affect inducible lateral-flagellum formation (7).…”

“…One open reading frame of lateralflagellum clusters of both species encodes a 54 -dependent response regulator, LafK, essential for lateral-flagellum generation (8,39). V. parahaemolyticus LafK is able to compensate for mutation of the polar-flagellum 54 -dependent response regulator, FlaK (19). The A. hydrophila FlrA mutation abolished polar-flagellum formation but did not affect lateral-flagellum-dependent swarming motility on semisolid medium; furthermore an A. hydrophila LafK mutation that abolished lateral-flagellum formation did not affect polar-flagellum biogenesis (7,8).…”

Characterization of the relationship between polar and lateral flagellar structural genes in the deep-sea bacterium Shewanella piezotolerans WP3

“…Additionally, the transcriptional hierarchy of the PF and LF systems has been shown to be specific with no interconnections1524. Although compensatory activation of PF genes by the LF regulator LafK has been demonstrated11, genetic experiments in V. parahaemolyticus , which has a dual flagellar system, suggested that there are no shared structural components among the two motility systems and that mutants unable to swarm retain swimming motility and vice versa10. An investigation of the dual flagellar system of Shewanella putrefaciens CN-32 also demonstrated that the motor components were highly specific and were unlikely to be shared between the two flagellar systems19.…”

“…Mutations affecting PF performance resulted in the production of LF in liquid medium10. Moreover, the LF regulator LafK could influence the expression of PF genes by compensatory activation11. Nevertheless, the relationship between the polar and lateral flagellar structural genes is still largely unknown.…”

Polar, Peritrichous, and Lateral Flagella Belong to Three Distinguishable Flagellar Families

“…9 We used either laf-mutants or the control of growth conditions to produce purified pof. 9,10 In an earlier paper, we named the major flagellar polymorph observed under physiological conditions left-handed curly (or L-Curly). However, this form would be called N by Leifson's definition, because it is the commonest polymorph under ordinary conditions.…”