The bacterial flagellum is a self-assembling macromolecular machine anchored in the bacterial membrane that allows bacteria to move through liquid environments or crawl along surfaces (Macnab 1992). Flagellar assembly and function is a complex process, which in Salmonella typhimurium involves over 60 genes (Frye et al. 2006). The construction of individual flagella requires an ordered assembly pathway (Macnab 1992). The assembly process involves the secretion of individual subunits through the hollow core of the growing flagellum where they assemble at the tip of the structure. In addition, multi-flagellated bacteria can have individual flagella in the same cell at different stages of assembly (Bardy et al. 2003). Consequently, the assembly process is tightly regulated at the levels of substrate selection by the associated secretion apparatus and coupled gene regulation. This paper reports an unexpected discovery related to the current understanding of how a cell regulates flagellar gene expression in response to intermediate stages of flagellar assembly. A flagellar-specific transcription factor, 28, plays a dual role as both a regulator of gene expression and a facilitator of flagellar-specific Type III secretion.The bacterial flagellum consists of three major substructures: (1) the basal body, which acts as motor anchoring the flagellum within the cell membranes; (2) the hook, which acts as a flexible, universal joint between the basal body; and (3) the long external filament, which acts as a propeller when rotated (Berg and Anderson 1973;Macnab 1999). Self-assembly of a flagellum begins at the inner membrane and proceeds out of the cell with construction of the basal structure. A flagellar-specific Type III secretion (T3S) apparatus is assembled within the cytoplasmic membrane at the base of the basal structure (Aldridge and Hughes 2002). Individual structural subunits are then secreted from the cytoplasm into the growing flagellum by the flagellar T3S system. Efficient flagellar assembly requires that the T3S apparatus distinguish between different secretion substrates at different stages of assembly. Recent studies have shown that there is a multi-layered regulatory network in place that couples temporal expression and delivery of flagellar
Bradyrhizobium japonicum is one of the soil bacteria that form nodules on soybean roots. The cell has two sets of flagellar systems, one thick flagellum and a few thin flagella, uniquely growing at subpolar positions. The thick flagellum appears to be semicoiled in morphology, and the thin flagella were in a tight-curly form as observed by dark-field microscopy. Flagellin genes were identified from the amino acid sequence of each flagellin. Flagellar genes for the thick flagellum are scattered into several clusters on the genome, while those genes for the thin flagellum are compactly organized in one cluster. Both types of flagella are powered by proton-driven motors. The swimming propulsion is supplied mainly by the thick flagellum. B. japonicum flagellar systems resemble the polar-lateral flagellar systems of Vibrio species but differ in several aspects.Bradyrhizobium japonicum is a nitrogen-fixing bacterial species that forms root nodules specifically on soybean (Glycine max) roots. Because soybeans are a good dietary source of protein for vegetarians, soybeans and hence B. japonicum are agriculturally important. The complete genome of B. japonicum has been sequenced (8). It retains both flagellar and type III secretion systems, which play a crucial role in plant-microorganism interactions, especially for bacterial adhesion to the root hair surfaces.Flagella of rhizobacterial species are different from those of enteric species. For example, Rhizobium lupini or Sinorhizobium meliloti has peritrichous flagella, but the flagellar filament shows a zigzag pattern on the surface, which is called the complex filament. The complex filament exhibits a prominent helical pattern of alternating ridges and grooves, thus appearing more complex than plain filaments of enteric bacteria (14,16). Azospirillum brasilense has two sets of flagellar systems (6): a polar flagellum and lateral flagella, similar to those of Vibrio parahaemolyticus (4, 11). V. parahaemolyticus cells swim in aqueous (low-viscosity) conditions by using a single polar flagellum as a screw, while they swarm on the viscous surface by using lateral flagella (9).In this study, we first observed B. japonicum cells by electron microscopy and were amazed about the unusual set of flagella, one thick flagellum and a few thin flagella, both growing from the side of the cell body. Thus, they are distinctive from the similar set of flagella of V. parahaemolyticus: polar flagellum and lateral flagella. We have purified the flagella separately from mutants, analyzed the component proteins by amino acid sequencing, and identified the genes encoding those proteins. We have also examined the role of each flagellum by microscopic observations of mutants that carry only one set of the flagella. MATERIALS AND METHODSBacterial strains and growth conditions. B. japonicum strain 110spc4 is a mutant derivative of B. japonicum USDA3I1b110. BJD⌬283 is a mutant with the deletion of flagellin genes bll6865 and bll6866, which are part of the set 2 cluster of flagellar genes. They en...
Background: Light-driven proton pumps are utilized to control the neural activity. Results: We have succeeded to produce a blue-shifted proton pump. The rotation of the -ionone ring contributes to the spectral shift. Conclusion: The designed color variant provides a tool that allows the control of neural activity by blue light. Significance: The knowledge will help to understand the color-tuning mechanism and can be utilized for optogenetics.
Precise regulation of the number and positioning of flagella are critical in order for the mono-polarflagellated bacterium Vibrio alginolyticus to swim efficiently. It has been shown that, in V. alginolyticus cells, the putative GTPase FlhF determines the polar location and production of flagella, while the putative ATPase FlhG interacts with FlhF, preventing it from localizing at the pole, and thus negatively regulating the flagellar number. In fact, no flhF cells have flagella, while a very small fraction of flhFG cells possess peritrichous flagella. In this study, the mutants that suppress inhibition of the swarming ability of flhFG cells were isolated. The mutation induced an increase in the flagellar number and, furthermore, most Vibrio cells appeared to have peritrichous flagella. The sequence of the flagella related genes was successfully determined, however, the location of the suppressor mutation could not been found. When the flhF gene was introduced into the suppressor mutant, multiple polar flagella were generated in addition to peritrichous flagella. On the other hand, introduction of the flhG gene resulted in the loss of most flagella. These results suggest that the role of FlhF is bypassed through a suppressor mutation which is not related to the flagellar genes.Key words bacterial flagellum, flagellar localization, flagellar number, polar flagellum.The bacterial flagellum is a locomotive organelle which is composed of a motor and a screw part. The motor is embedded in the cell envelope and driven by ion motive force. The screw part is composed of a helical filament which is connected to the motor via a hook. This hook acts as a universal joint between the two structures. Flagellar assembly begins with formation of the membrane-embedded motor part, after which the hook structure is constructed. Finally the filament is polymerized from the proximal end towards the distal tip. It is believed that formation of an ‡ These authors contributed equally to this work. MS ring by the membrane protein FliF is the first step towards flagellar morphogenesis. After this soluble proteins (FliG, FliM, and FliN) are attached to the cytoplasmic side of the MS ring, forming the C ring. Then a specific apparatus used for flagellar protein export is assembled inside the C ring, which acts as the entrance to the channel for flagellar proteins (1). The number and localization of flagella vary between species (2). For example, V. alginolyticus and V. parahaemolyticus have both peritrichous (or lateral) flagella 76
Sensory rhodopsin I (SRI) functions as a dual receptor regulating both negative and positive phototaxis. It transmits light signals through changes in protein-protein interactions with its transducer protein, HtrI. The phototaxis function of Halobacterium salinarum SRI (HsSRI) has been well characterized using genetic and molecular techniques, whereas that of Salinibacter ruber SRI (SrSRI) has not. SrSRI has the advantage of high protein stability compared with HsSRI and, therefore, provided new information about structural changes and Cl(-) binding of SRI. However, nothing is known about the functional role of SrSRI in phototaxis behavior. In this study, we expressed a SRI homologue from the archaeon Haloarcula vallismortis (HvSRI) as a recombinant protein which uses all-trans-retinal as a chromophore. Functionally important residues of HsSRI are completely conserved in HvSRI (unlike in SrSRI), and HvSRI is extremely stable in buffers without Cl(-). Taking advantage of the high stability, we characterized the photochemical properties of HvSRI under acidic and basic conditions and observed the effects of Cl(-) on the protein under both conditions. Fourier transform infrared results revealed that the structural changes in HvSRI were quite similar to those in HsSRI and SrSRI. Thus, HvSRI can become a useful protein model for improving our understanding of the molecular mechanism of the dual photosensing by SRI.
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