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CheR- and CheB-dependent chemosensory adaptation system of Rhodobacter sphaeroides
A C Martin1, G H Wadhams, D S Shah
1Microbiology Unit, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom.
Journal of Bacteriology
|November 22, 2001
Summary
Rhodobacter sphaeroides CheR(2) and CheB(1) are crucial for chemotaxis, unlike CheR(1). These proteins complement E. coli mutants but don't affect McpG localization, suggesting distinct adaptation mechanisms in bacteria.
Area of Science:
- Microbiology
- Bacterial Chemotaxis
- Signal Transduction
Background:
- Rhodobacter sphaeroides possesses multiple chemotaxis gene homologues, organized in operons and other loci, similar to Escherichia coli.
- Key genes include cheA(1), cheR(1) (che Op(1)), and cheA(2), cheR(2), cheB(1) (che Op(2)).
Purpose of the Study:
- To investigate the roles of Rhodobacter sphaeroides chemotaxis gene homologues CheR(1), CheR(2), and CheB(1) in chemosensory behavior.
- To determine if these proteins can complement Escherichia coli chemotaxis mutants.
- To assess the involvement of these proteins in the polar localization of the chemoreceptor McpG.
Main Methods:
- Construction of in-frame deletions in cheR and cheB homologues in R. sphaeroides.
- Examination of chemosensory behavior using swarm plates and tethered cell assays.
- Complementary assays with Escherichia coli chemotaxis mutants.
- Analysis of McpG localization.
- Methanol release measurements to study adaptation mechanisms.
- In vitro phosphorylation assays with CheA and CheB proteins.
Main Results:
- CheR(2) and CheB(1) are essential for normal chemotaxis in R. sphaeroides, while CheR(1) is not.
- cheR(2) and cheB(1) successfully complemented equivalent E. coli mutants.
- None of the studied proteins were required for the polar localization of McpG.
- R. sphaeroides exhibits a unique adaptation system, with methanol release observed upon attractant addition but not removal.
- CheA(2) phosphorylates CheB(1), but CheA(1) does not, indicating distinct signaling pathways for adaptation.
Conclusions:
- CheR(2) and CheB(1) play critical roles in R. sphaeroides chemotaxis and adaptation, potentially interacting with conserved regions of methyl-accepting chemotaxis proteins (MCPs).
- The chemotaxis adaptation system in R. sphaeroides differs significantly from those in E. coli and Bacillus subtilis.
- Distinct CheA/CheB signaling pathways mediate chemotaxis and adaptation in R. sphaeroides.