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We have characterized open reading frame RSP0072, which is located within the flgG operon in Rhodobacter sphaeroides. The amino acid sequence analysis of this gene product showed the presence of a soluble lytic transglycosylase domain. The deletion of the N-terminal region (90 amino acids) of the product of RSP0072 yields a leaky nonmotile phenotype, as determined by swarm assays in soft agar. Electron micrographs revealed the lack of flagella in mutant cells. The purified wild-type protein showed lytic activity on extracts of Micrococcus luteus. In contrast, no lytic activity was observed when the residues E57 or E83 were replaced by alanine. Affinity blotting suggests that the protein encoded by RSP0072 interacts with the flagellar rod-scaffolding protein FlgJ, which lacks the muramidase domain present in FlgJ of many bacteria. We propose that the product of RSP0072 is a flagellar muramidase that is exported to the periplasm via the Sec pathway, where it interacts with FlgJ to open a gap in the peptidoglycan layer for the subsequent penetration of the nascent flagellar structure.

Rhodobacter sphaeroides expresses two different flagellar systems, a subpolar flagellum (fla1) and multiple polar flagella (fla2). These structures are encoded by different sets of flagellar genes. The chemotactic control of the subpolar flagellum (fla1) is mediated by three of the six different CheY proteins (CheY6, CheY4, or CheY3). We show evidence that CheY1, CheY2, and CheY5 control the chemotactic behavior mediated by fla2 flagella and that RSP6099 encodes the fla2 FliM protein.Many bacteria move by using flagella as the locomotive organelle. Flagella alternate between clockwise and counterclockwise rotation or in some cases between rotation and brief stop periods, which allow the bacterial cell to swim in a linear trajectory or to reorient (1,14,15). Bacterial taxis is achieved by modifying the frequency of reorientation events. The bias in the frequency of reorientation is modified by the interaction of the phosphorylated form of the response regulator CheY-P with the switch protein (FliM), which is part of the motor-switch structure located at the base of the flagellum. The concentration of CheY-P is regulated by the chemotactic system (3).A limited number of bacteria possess dual flagellar systems and are able to express two different flagellum types: a polar flagellum for swimming and lateral flagella for swarming; these microorganisms include Vibrio parahaemolyticus (27), Vibrio alginolyticus (8), Aeromonas spp. (26), Azospirillum brasilense (18), Rhodospirillum centenum (17), Helicobacter mustelae (19), and Plesiomonas shigelloides (7). The best-characterized examples are those that belong to the Vibrio genus. The ability to synthesize two different types of flagella allows these microorganisms to populate various niches (16).Rhodobacter sphaeroides is a facultative nonsulfur photosynthetic bacterium. Its genome sequence revealed many intriguing features related to motility and chemotaxis (13), including the presence of two flagellar gene sets. The genes that belong to the first set (fla1) are expressed constitutively and allow the strong swimming previously reported for the WS8 wild-type strain (1,10,21,22). The genes of the second flagellar set are not expressed in the wild-type WS8 strain; however, strains that express it can be isolated. In contrast with the case for other dual-flagellum systems, the fla2 genes of R. sphaeroides produce polar flagella that allow swimming (21).Several chemotactic genes are also reiterated (two cheB genes, three cheR genes, four cheA and cheW genes, and six cheY genes). In spite of this, only some of these gene copies are required when the cell is swimming with the fla1 flagellum. For example, it has been reported that only CheY6 and either CheY3 or CheY4 are required for chemotaxis mediated by the fla1 flagellum (23), despite the fact that the six cheY genes are expressed (6). The presence of a second functional flagellum in R. sphaeroides suggests that some of the chemotactic genes could be involved in its tactic control. To test this hypothesis, we investigated...

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In this work we identified the flgE gene encoding the flagellar hook protein from Rhodobacter sphaeroides. Our results show that this gene is part of a flagellar cluster that includes the genes flgB, flgC, flgD, flgE, and flgF. Two different types of mutants in the flgE gene were isolated, and both showed a Fla ؊ phenotype, indicating the functionality of this sequence. Complementation studies of these mutant strains suggest that flgE is included in a single transcriptional unit that starts in flgB and ends in flgF. In agreement with this possibility, a specific transcript of approximately 3.5 kb was identified by Northern blot. This mRNA is large enough to represent the complete flgBCDEF operon. FlgE showed a relatively high proline content; in particular, a region of 12 amino acids near the N terminus, in which four prolines were identified. Cells expressing a mutant FlgE protein lacking this region showed abnormal swimming behavior, and their hooks were curved. These results suggest that this region is involved in the characteristic quaternary structure of the hook of R. sphaeroides and also imply that a straight hook, or perhaps the rigidity associated with this feature, is important for an efficient swimming behavior in this bacterium.Salmonella enterica serovar Typhimurium swims toward favorable environments in response to changes in the surrounding medium using its flagella; these appendages consist basically of a helical filament driven by a rotary motor. When flagella rotate in counterclockwise direction, the filaments coalesce in a bundle that functions as a propeller to push the bacterial cell body in a linear trajectory. On the contrary, when flagella reverse the sense of rotation the bundle is no longer stable, and the uncoordinated movement of each flagellum causes the cell to tumble. As revealed by early studies of electron microscopy, the flagellum consists of a filament, a curved hook, and a basal body (6). The filament and the hook are each composed of repeats of a single protein, flagellin and hook protein, respectively. These polypeptides do not share extensive similarity at the level of its primary sequence but both have the ability to self-assemble, and the resulting structures are capable of displaying polymorphic transitions; this capability has been suggested to be important in the motility of certain species of bacteria (12,16,22).The structure of the filament has been the subject of extensive study during the last few decades, and various structural models have been proposed (18,21,33,37). In contrast, the hook structure has been less well characterized; however, since the hook protein shares important features with flagellin, it has been suggested that hook and flagellin subunits have a similar folding pattern (20,34,35,36).The detailed knowledge about the structure and function of the flagellum in enterobacteria contrasts strongly with the limited data on these aspects that exist for other bacterial groups. However, it seems clear that as far as structure and function are concerned, ...