Characterization of Two Outer Membrane Proteins, FlgO and FlgP, That Influence Vibrio cholerae Motility

Abstract

FlgO is an outer membrane protein that localizes throughout the membrane and not at the flagellar pole. Although FlgO and FlgP do not specifically localize to the flagellum, they are required for flagellar stability. Due to the nature of these motility defects, we established that the flagellum is not sufficient for adherence; rather, motility is the essential factor required for attachment and thus colonization by V. cholerae O1 of the classical biotype. This study reveals a novel mechanism for which the outer membrane proteins FlgO and FlgP function in motility to mediate flagellar stability and influence attachment and colonization.The causative agent of the infectious diarrheal disease cholera is the bacterium Vibrio cholerae. This enteric pathogen naturally inhabits an aquatic environment and is motile by the action of a single polar flagellum. The mechanism of pathogenesis by which V. cholerae causes disease is a stepwise and cyclic process. First, contaminated food or water is ingested; then, the bacteria pass through the stomach. After withstanding that acidic environment, the bacteria enter the lumen of the intestine and attach to the intestinal epithelium of the human host. Once the bacteria establish an initial attachment, the bacteria begin to express the toxin-coregulated pilus, which facilitates bacterium-bacterium interactions and the formation of microcolonies. Subsequently, an enterotoxin, cholera toxin, is expressed and secreted by the bacteria, which through a cascade of events leads to profuse, watery diarrhea. Eventually, the bacteria are shed from the host and are dispersed back into the environment, thus renewing the cycle.Although the later stages of the disease, which include the production of toxin-coregulated pilus and cholera toxin, are well characterized, little is known about the initial stages of pathogenesis. The attachment factor GbpA has been shown to bind chitin, an abundant substance found in the environment that is a polymer of N-acetylglucosamine (GlcNAc) carbohydrate subunits (17). GbpA is also involved in the initial attachment of V. cholerae to epithelial cells, which have exposed GlcNAc moieties on their surfaces. In the absence of gbpA, only a 50% reduction in attachment is observed, suggesting that there may be additional factors that are involved in initiating attachment to the intestinal epithelium.Colonization requires a functional flagellum; therefore, motility is a crucial virulence factor of V. cholerae (9, 12). The flagellum functions to propel the cell through its environment. In the host, the flagellum functions as a means to gain access to the microvilli of the epithelial cells by facilitating the penetration of the intestinal mucus layer, an action that is important for colonization (1,4,14). The flagellum is composed of a base, a hook, and a filament. The flagellar apparatus is assembled in an ordered cascade of events. The genes necessary for motility and chemotaxis are found distributed among six regions on the large chromosome of V. cholerae (regions I t...

The Flagellar Basal Body-Associated Protein FlgT Is Essential for a Novel Ring Structure in the Sodium-Driven Vibrio Motor

“…(28). The flgO and flgP genes are located in the region next to the flgT gene on genome, and it has been reported that flagella in a flgO or flgP mutant are shorter in length than wild-type flagella (28). Further work needs to be done to identify all of the components contained in the purified basal body fraction.…”

“…P, periplasmic fraction; F, flowthrough fraction; E, eluted fraction. (28). The flgO and flgP genes are located in the region next to the flgT gene on genome, and it has been reported that flagella in a flgO or flgP mutant are shorter in length than wild-type flagella (28).…”

Insight into the assembly mechanism in the supramolecular rings of the sodium-driven Vibrio flagellar motor from the structure of FlgT

“…Unknown H-ring components assemble around the LP ring to form the complete H ring. FlgO and FlgP might be potential candidates as the outer part of the H ring because they are outer membrane proteins (26). The MotX-MotY complex then associates with the basal body through MotY-N to form the T ring.…”

Vibrio cholerae Flagellar Synthesis and Virulence

“…FlgO homologues are only found in Vibrio spp. V. cholerae strains lacking flgO have a similar phenotype as flgP strains, namely they produce fragile flagella that break easily while swimming (Morris, Peng et al 2008;Martinez, Dharmasena et al 2009). …”

“…FlgP homologues are restricted to Vibrio, Helicobacter, and Campylobacter spp. V. cholerae FlgP is a lipoprotein that affects flagellar stability; flgP mutants synthesize fragile flagella and appear non-motile in motility agar, presumably due to breakage of flagella during swimming (Morris, Peng et al 2008;Martinez, Dharmasena et al 2009). FlgO homologues are only found in Vibrio spp.…”