Identification of a chemotaxis operon with two cheY genes in Rhodobacter sphaeroides

Abstract

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 overexpressed 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the chemotaxis protein CheW from Rhodobacter sphaeroides and its effect on the behaviour of Escherichia coli

“…Deletion of cheW produces enhanced responses, under aerobic and anaerobic conditions, to the addition and removal of sugars such as mannitol and fructose. This behaviour is also seen in R. sphaeroides cheA mutant tethered cells which showed an enhanced response to fructose even though responses to all other chemoeffectors remained apparently normal (Ward et al, 1995a). These data suggest that cheW and cheA may form a signal-transduction pathway involved in controlling the strength and type of response to sugars such as mannitol and fructose.…”

“…Previous studies suggested that the expression of the R. sphaeroides cheW gene may interfere with the chemosensory signal-transduction pathway of E. coli (Ward et al, 1995a). To analyse this further, the R. sphaeroides cheW gene was cloned into the IPTG-inducible E. coli expression vector pTM30 such that cheW was under the control of the ptac promoter.…”

“…What, then, is the role of the chemotaxis genes in R. sphaeroides? Ward et al (1995a) have shown that interruption of the cheA gene had no effect on tactic response to organic acids, whilst responses to sugars were inverted and enhanced. This phenotype is significantly different from that of E. coli where deletion of cheA results in a chemotaxis-minus, smooth-swimming strain.…”

Analysis of a chemotaxis operon from Rhodospirillum centenum

“…Thus, R. centenum has two CheY homologs, one fused to CheA and the other free existing. More than one CheY homolog has been reported to exist in the photosynthetic bacterium Rhodobacter sphaeroides (44) as well as in Rhizobium meliloti (13). A dendograph of the various CheY proteins indicates that the R. sphaeroides and R. meliloti CheY1 proteins form a separate lineage from the CheY2 proteins of these species (Fig.…”

Metabolism is required for chemotaxis to sugars in Rhodobacter sphaeroides

“…A chemotaxis operon has been identified in R. sphaeroides containing homologues of the enteric cheA, chew, cheR and two cheY genes, but lacking cheB and cheZ homologues (Ward et al, 1995a). In contrast to the enterics, mutation of these chemotaxis genes in R. sphaeroides has little effect on chemotaxis to most chemoattractants (Hamblin et al, 1997).…”