Analysis of the Polar Flagellar Gene System of Vibrio parahaemolyticus

Abstract

Vibrio parahaemolyticus has dual flagellar systems adapted for locomotion under different circumstances. A single, sheathed polar flagellum propels the swimmer cell in liquid environments. Numerous unsheathed lateral flagella move the swarmer cell over surfaces. The polar flagellum is produced continuously, whereas the synthesis of lateral flagella is induced under conditions that impede the function of the polar flagellum, e.g., in viscous environments or on surfaces. Thus, the organism possesses two large gene networks that orchestrate polar and lateral flagellar gene expression and assembly. In addition, the polar flagellum functions as a mechanosensor controlling lateral gene expression. In order to gain insight into the genetic circuitry controlling motility and surface sensing, we have sought to define the polar flagellar gene system. The hierarchy of regulation appears to be different from the polar system of Caulobacter crescentus or the peritrichous system of enteric bacteria but is pertinent to many Vibrio and Pseudomonas species. The gene identity and organization of 60 potential flagellar and chemotaxis genes are described. Conserved sequences are defined for two classes of polar flagellar promoters. Phenotypic and genotypic analysis of mutant strains with defects in swimming motility coupled with primer extension analysis of flagellar and chemotaxis transcription provides insight into the polar flagellar organelle, its assembly, and regulation of gene expression.Many bacterial species are motile by means of flagellar propulsion (reviewed in references 5, 32, and 33). Powered by a rotary motor, the flagellum acts as semirigid helical propeller, which is attached via a flexible coupling, known as the hook, to the basal body. The basal body consists of rings and rods that penetrate the membrane and peptidoglycan layers. Associating with the basal body and projecting into the cytoplasm is a structure termed the C ring, which contains the switch proteins and acts as the core, or rotating part, of the motor. Maintenance of a flagellar motility system is a sizable investment with respect to cellular economy in terms of the number of genes and the energy that must be committed to gene expression, protein synthesis, and flagellar rotation. As a result, flagellar systems are highly regulated. A hierarchy of regulation has been elucidated for peritrichously flagellated Escherichia coli and Salmonella enterica serovar Typhimurium (26,27,30). This scheme of control couples gene expression to assembly of the organelle. The pyramid of expression possesses three classes, or tiers, of genes. Genes in each class must be functional in order for expression of the subsequent class to occur. Class 1 genes, flhD and flhC, encode the master transcriptional activators of class 2 flagellar gene expression. The flhDC operon is controlled by a 70 promoter and a number of global regulatory factors (28). The majority of the class 2 flagellar genes encode components of the flagellar export system and the basal body (21). One clas...

FlhF, a signal recognition particle-like GTPase, is involved in the regulation of flagellar arrangement, motility behaviour and protein secretion in Bacillus cereus

“…2a). The flhA gene, which encodes a membrane protein that is part of the flagellar export apparatus Minamino & Macnab, 1999), is located upstream of flhF in B. cereus, as well as in many other bacteria (Carpenter et al, 1992;Dasgupta et al, 2000;Kim & McCarter, 2000;Kusumoto et al, 2006;Pandza et al, 2000). In contrast, only in B. cereus, the gene downstream of flhF is flgG, which encodes the flagellar basal body rod protein in many micro-organisms (Minamino & Macnab, 1999;Zuberi et al, 1991).…”

“…In fact, depending upon the genetic background of B. subtilis, flhF disruption has been reported to differently affect the motility phenotype of this species (Carpenter et al, 1992;Zanen et al, 2004). In all bacterial species studied so far, the protein encoded by flhF shares substantial homology with proteins of the GTP-binding signal recognition particle (SRP) family (Carpenter et al, 1992;Kim & McCarter, 2000;Pandza et al, 2000), such as Ffh and FtsY. However, while Ffh and FtsY are required for targeting many secretory and membrane proteins to the plasma membrane (for a review see Halic & Beckmann, 2005), an involvement of FlhF in protein secretion has been demonstrated only in P. putida (Pandza et al, 2000).…”

The Pseudomonas fluorescens transcription activator AdnA is required for adhesion and motility The GenBank accession number for the sequence reported in this paper is AF312695.

“…The function of orf99 is unknown, but it shares similarity with its positional homologue in P. aeruginosa, orf97. Regions with a similar or identical genetic organization are found in P. aeruginosa, Vibrio cholerae and Vibrio parahaemolyticus (Arora et al, 1997 ;Klose & Mekalanos, 1998a ;Kim & McCarter, 2000).…”

“…Although the conserved aspartate residue is missing, serine and threonine can be phosphorylated, leaving open the possibility that an unrecoginzed kinase exists for AdnA. The regions immediately downstream of fleQ, flaK and flrA contain σ&%-dependent, two-component systems named fleSR, flaLM and flrBC (Ritchings et al, 1995 ;Klose & Mekalanos, 1998a ;Kim & McCarter, 2000). Transcription of fleSR and flrBC is activated by FleQ and FlrA, respectively, so it seems likely that the P. fluorescens fleSR homologues will be regulated by AdnA.…”

Integration of Global Regulatory Mechanisms Controlling Vibrio Cholerae Behavior

“…Genes required for flagellum rotation include pomA (motA), pomB (motB), motX, motY, fliG, fliM and fliN. Inactivation of motA motB, motY or motX by mutation abolish motility but does not prevent flagellum assembly (Boles & McCarter, 2000;Kim & McCarter, 2000;McCarter, 2001). MotA and MotB translocate Na + by forming the Na + conducting channel; MotX and MotY are required for torque generation (Asai et al, 1997).…”