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  • 1
    Digitale Medien
    Digitale Medien
    Sensory Transduction in Flagellate Bacteria (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 510 (1987), S. 0 
    Details
    ISSN: 1749-6632
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Allgemeine Naturwissenschaft
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1749-6632.1987.tb43459.x
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  • 2
    Digitale Medien
    Digitale Medien
    The roles of the multiple CheW and CheA homologues in chemotaxis and in chemoreceptor localization in Rhodobacter sphaeroides (2001)
    Oxford, UK : Blackwell Science, Ltd
    Molecular microbiology 40 (2001), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Rhodobacter sphaeroides has multiple homologues of most of the Escherichia coli chemotaxis genes, organized in two major operons and other, unlinked, loci. These include cheA1 and cheW1 (che Op1) and cheA2, cheW2 and cheW3 (che Op2). We have deleted each of these cheA and cheW homologues in-frame and examined the chemosensory behaviour of these strains on swarm plates and in tethered cell assays. In addition, we have examined the effect of these deletions on the polar localization of the chemoreceptor McpG. In E. coli, deletion of either cheA or cheW results in a non-chemotactic phenotype, and these strains also show no receptor clustering. Here, we demonstrate that CheW2 and CheA2 are required for the normal localization of McpG and for normal chemotactic responses under both aerobic and photoheterotrophic conditions. Under aerobic conditions, deletion of cheW3 has no significant effect on McpG localization and only has an effect on chemotaxis to shallow gradients in swarm plates. Under photoheterotrophic conditions, however, CheW3 is required for McpG localization and also for chemotaxis both on swarm plates and in the tethered cell assay. These phenotypes are not a direct result of delocalization of McpG, as this chemoreceptor does not mediate chemotaxis to any of the compounds tested and can therefore be considered a marker for general methyl-accepting chemotaxis protein (MCP) clustering. Thus, there is a correlation between the normal localization of McpG (and presumably other chemoreceptors) and chemotaxis. We propose a model in which the multiple different MCPs in R. sphaeroides are contained within a polar chemoreceptor cluster. Deletion of cheW2 and cheA2 under both aerobic and photoheterotrophic conditions, and cheW3 under photoheterotrophic conditions, disrupts the cluster and hence reduces chemotaxis to any compound sensed by these MCPs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.2001.02468.x
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  • 3
    Digitale Medien
    Digitale Medien
    Inverted behavioural responses in wild-type Rhodobacter sphaeroides to temporal stimuli (2000)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 189 (2000), S. 0 
    Details
    ISSN: 1574-6968
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Both aerobically and photosynthetically grown wild-type Rhodobacter sphaeroides swarmed through soft nutrient agar. However, individual aerobically and photosynthetically grown tethered cells showed different responses to steps in concentrations of some attractants. Photosynthetically grown cells showed little response to a step-up in attractant, but large response to a step-down. Aerobically grown cells showed a large but opposite response to a step-up of chemoeffectors such as succinate and aspartate. The responses in che operon deletion mutants were also investigated and indicated that the aerobic response may depend on the protein products of che operon 1.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1574-6968.2000.tb09247.x
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  • 4
    Digitale Medien
    Digitale Medien
    Identification and localization of a methyl-accepting chemotaxis protein in Rhodobacter sphaeroides (2000)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 36 (2000), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Genes coding for a classical membrane spanning chemoreceptor (mcpG) and a response regulator (cheY4) were identified in a region of Rhodobacter sphaeroides DNA unlinked to either of the two previously identified chemosensory operons. Immunogold electron microscopy had shown that the expression of chemoreceptors in R. sphaeroides varies with growth conditions. Using GFP fused to the newly identified McpG, we examined the targeting of this single methyl-accepting chemotaxis protein (MCP) under different growth conditions. The gene encoding the C-terminal McpG–GFP fusion was introduced by homologous recombination into the chromosome, replacing the wild-type gene. The resultant protein localized to the poles of the cell under aerobic, photoheterotrophic and anaerobic dark conditions, demonstrating that this MCP is expressed under all three growth conditions. More protein was always found at one pole than the other. The polar fluorescence increased during the cell cycle, with protein becoming evident at the second pole around the time of septation. At division, each daughter cell had a label at one pole, but the intensity of fluorescence was higher in the daughter cell containing the original labelled pole. McpG localization was not altered in a che Operon 1 deletion strain, lacking CheW1 and CheA1, but a che Operon 2 deletion strain, lacking CheW2, CheW3 and CheA2, showed significantly reduced polar localization. This observation indicates that polar localization of McpG depends on Che proteins encoded by Operon 2, but not homologues encoded by Operon 1.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.01936.x
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  • 5
    Digitale Medien
    Digitale Medien
    Characterization of the chemotaxis protein CheW from Rhodobacter sphaeroides and its effect on the behaviour of Escherichia coli (1997)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 24 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: In contrast to the situation in enteric bacteria, chemotaxis in Rhodobacter sphaeroides requires transport and partial metabolism of chemoattractants. A chemotaxis operon has been identified containing homologues of the enteric cheA, cheW, cheR genes and two homologues of the cheY gene. However, mutations in these genes have only minor effects on chemotaxis. In enteric species, CheW transmits sensory information from the chemoreceptors to the histidine protein kinase, CheA. Expression of R. sphaeroidescheW in Escherichia coli showed concentration-dependent inhibition of wild-type behaviour, increasing counter-clockwise rotation and thus smooth swimming — a phenotype also seen when E. coli cheW is overexpressed in E. coli. In contrast, overexpression of R. sphaeroidescheW in wild-type R. sphaeroides inhibited motility completely, the equivalent of inducing tumbly motility in E. coli. Expression of R. sphaeroides cheW in an E. coliΔcheW chemotaxis mutant complemented this mutation, confirming that CheW is involved in chemosensory signal transduction. However, unlike E. coliΔcheW mutants, in-frame deletion of R. sphaeroides cheW did not affect either swimming behaviour or chemotaxis to weak organic acids, although the responses to sugars were enhanced. Therefore, although CheW may act as a signal-transduction protein in R. sphaeroides, it may have an unusual role in controlling the rotation of the flagellar motor. Furthermore, the ability of a ΔcheW mutant to swim normally and show wild-type responses to weak acids supports the existence of additional chemosensory signal-transduction pathways.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.3241682.x
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  • 6
    Digitale Medien
    Digitale Medien
    Identification of a chemotaxis operon with two cheY genes in Rhodobacter sphaeroides (1995)
    Osney Mead, Oxford OX2 0EL, UK : Blackwell Scientific Publications
    Molecular microbiology 17 (1995), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: A large chemotaxis operon was identified in Rhodobacter sphaeroides WS8-N using a probe based on the 3′ terminal portion of the Rhizobium meliloti cheA gene. Two genes homologous to the enteric cheY were identified in an operon also containing cheA, cheW, and cheR homologues. The deduced protein sequences of che gene products were aligned with those from Escherichia coli and shown to be highly conserved. A mutant with an interrupted copy of cheA showed normal patterns of swimming, unlike the equivalent mutants in E. coli which are smooth swimming. Tethered cheA mutant cells showed normal responses to changes in organic acids, but increased, inverted responses to sugars. The unusual behaviour of the cheA mutant and the identification of two homologues of cheY suggests that R. sphaeroides has at least two pathways controlling motor activity. To identify functional similarity between the newly identified R. sphaeroides Che pathway and the methyl-accepting chemotaxis protein (MCP)-dependent pathway in enteric bacteria, the R. sphaeroides cheW gene was expressed in a cheW mutant strain of E. coli and found to complement, causing a partial return to a swarming phenotype. In addition, expression of the R. sphaeroides gene in wild-type E. coli resulted in the same increased tumbling and reduced swarming as seen when the native gene is over-expressed in E. coli. The identification of che homologues in R. sphaeroides and complementation by cheW suggests the presence of MCPs in an organism previously considered to use only MCP-independent sensing. The MCP-dependent pathway, appears conserved. In R. sphaeroides this pathway may mediate responses to sugars, while responses to organic acids may in involve a second system, possibly using the second CheY protein identified in this study.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.mmi_17020357.x
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  • 7
    Digitale Medien
    Digitale Medien
    The third chemotaxis locus of Rhodobacter sphaeroides is essential for chemotaxis (2002)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 46 (2002), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: The purple photosynthetic bacterium Rhodobacter sphaeroides has three loci encoding multiple homologues of the bacterial chemosensory proteins: 13 putative chemoreceptors, four CheW, four CheA, six CheY, two CheB and three CheR. Previously, studies have shown that, although deletion of cheOp1 led to only minor changes in behaviour, deletion of cheOp2 led to a loss of taxis. The third locus encodes two CheA, one CheR, one CheB, one CheW, one CheY, a putative cytoplasmic chemoreceptor (TlpT) and a protein showing homology to the chromosomal partitioning factor Soj (designated Slp). Here, we show that every protein encoded by this locus is essential for normal chemotaxis. Phototaxis is also dependent upon all the components of this locus, except CheB2 and Slp. The two putative CheA proteins encoded in this locus are unusual. CheA3 has only the P1 domain and the P5 regulatory domain linked by a large internal domain, whereas CheA4 lacks the P1 and P2 domains required for phosphorylation and response regulator binding. These data indicate that the minimal set of proteins required for normal chemotaxis in R. sphaeroides is all the proteins encoded by cheOp2 and the third chemotaxis locus, and that the multiple chemosensory protein homologues found in R. sphaeroides are not redundant.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.2002.03218.x
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  • 8
    Digitale Medien
    Digitale Medien
    Identification of a methyl-accepting chemotaxis protein in Rhodobacter sphaeroides (1995)
    Osney Mead, Oxford OX2 0EL, UK : Blackwell Science Ltd
    Molecular microbiology 18 (1995), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Analysis of the DNA sequence directly upstream of the chemotaxis operon of Rhodobacter sphaeroides identified a single gene whose product has strong similarity to the methyl-accepting chemotaxis proteins (MCPs) found in enteric bacteria. The deduced protein had a highly conserved signalling sequence and only one very hydrophobic region at the N-terminus, in contrast to enteric MCPs. A possible cytoplasmic location of the majority of the protein was supported by Western blotting. The mcpA gene was insertionally inactivated and the resulting phenotype examined using swarm plate assays. The mutant lacking McpA lost chemotaxis to a wide range of attractant stimuli but only under aerobic conditions; it retained almost normal chemotaxis under anaerobic/photosynthetic conditions. The identification of a sensory protein which is active only under one set of growth conditions suggests that R. sphaeroides probably has several MCPs, which co-ordinately respond to changes in environmental conditions. Southern hybridization at relaxed stringency to the conserved sequence of the R. sphaeroides and Caulobacter crescentus mcp genes identified three possible additional mcp genes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.mmi_18010115.x
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  • 9
    Digitale Medien
    Digitale Medien
    Identification of a fourth cheY gene in Rhodobacter sphaeroides and interspecies interaction within the bacterial chemotaxis signal transduction pathway (2000)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 35 (2000), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: The Escherichia coli chemotaxis signal transduction pathway has: CheA, a histidine protein kinase; CheW, a linker between CheA and sensory proteins; CheY, the effector; and CheZ, a signal terminator. Rhodobacter sphaeroides has multiple copies of these proteins (2 × CheA, 3 × CheW and 3 × CheY, but no CheZ). In this study, we found a fourth cheY and expressed these R. sphaeroides proteins in E. coli. CheA2 (but not CheA1) restored swarming to an E. coli cheA mutant (RP9535). CheW3 (but not CheW2) restored swarming to a cheW mutant of E. coli (RP4606). R. sphaeroides CheYs did not affect E. coli lacking CheY, but restored swarming to a cheZ strain (RP1616), indicating that they can act as signal terminators in E. coli. An E. coli CheY, which is phosphorylated but cannot bind the motor (CheY109KR), was expressed in RP1616 but had no effect. Overexpression of CheA2, CheW2, CheW3, CheY1, CheY3 and CheY4 inhibited chemotaxis of wild-type E. coli (RP437) by increasing its smooth-swimming bias. While some R. sphaeroides proteins restore tumbling to smooth-swimming E. coli mutants, their activity is not controlled by the chemosensory receptors. R. sphaeroides possesses a phosphorelay cascade compatible with that of E. coli, but has additional incompatible homologues.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.01680.x
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  • 10
    Digitale Medien
    Digitale Medien
    Localization and environmental regulation of MCP-like proteins in Rhodobacter sphaeroides (1999)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 31 (1999), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Chemotaxis to many compounds by Rhodobacter sphaeroides requires transport and at least partial metabolism of the chemoeffector. Previous investigations using phototrophically grown cells have failed to find any homologues of the MCP chemoreceptors identified in Escherichia coli. However, using an antibody raised against the highly conserved domain of E. coli Tsr, MCP-like proteins were identified in R. sphaeroides WS8N. Analysis using Western blotting and immunogold electron microscopy showed that expression of these MCP-like proteins is environmentally regulated and that receptors are targeted to two different cellular locations: the poles of the cells and the cytoplasm. In aerobically grown cells, these proteins were shown by immunoelectron microscopy to localize predominantly to the cell poles and to an electron-dense body in the cytoplasm. Western blot analysis indicated a 17-fold reduction in protein concentration when cells were grown in the light. The number of immunogold particles was also dramatically reduced in anaerobically light-grown cells and their cellular distribution was altered. Fewer receptors localized to the cell poles and more particles randomly distributed within the cell, but the cytoplasmic cluster remained. These trends were more pronounced in cells grown anaerobically under dim light than in those grown anaerobically under bright light, suggesting that expression is controlled by redox state and either light intensity or the extent of photosynthetic membrane synthesis. Recent work on E. coli chemosensing suggests that oligomerization of receptors and chemosensory proteins is important for sensory signalling. The data presented here suggest that this oligomerization can occur with cytoplasmic receptors and also provides an explanation for the multiple copies of chemosensory proteins in R. sphaeroides.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.1999.01226.x
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