Identification of a methyl-accepting chemotaxis protein in Rhodobacter sphaeroides

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Physiology

Background:

• Chemotaxis, the directed movement of bacteria in response to chemical stimuli, is vital for microbial survival and adaptation.
• Methyl-accepting chemotaxis proteins (MCPs) are key sensory transducers in bacterial chemotaxis pathways, particularly well-studied in enteric bacteria.
• Rhodobacter sphaeroides, a versatile bacterium, exhibits complex behavioral responses, necessitating an understanding of its chemotaxis machinery.

Purpose of the Study:

• To identify and characterize novel chemotaxis genes in Rhodobacter sphaeroides.
• To investigate the function of a newly identified methyl-accepting chemotaxis protein (MCP) homolog, designated McpA.
• To explore the environmental regulation of chemotaxis in R. sphaeroides.

Main Methods:

• Bioinformatic analysis of DNA sequences upstream of the chemotaxis operon.
• Gene inactivation via insertional mutagenesis of the identified mcpA gene.
• Phenotypic analysis using swarm plate assays under aerobic and anaerobic/photosynthetic conditions.
• Western blotting to determine protein localization.
• Southern hybridization to identify related genes.

Main Results:

• A novel gene, mcpA, encoding an MCP with unique structural features (single hydrophobic N-terminal region) was identified in R. sphaeroides.
• The McpA protein was found to be predominantly located in the cytoplasm.
• Mutants lacking functional McpA exhibited a significant loss of chemotaxis to various attractants under aerobic conditions but retained chemotaxis under anaerobic/photosynthetic conditions.
• Southern hybridization suggested the presence of at least three additional mcp genes in R. sphaeroides.

Conclusions:

• Rhodobacter sphaeroides possesses a unique MCP, McpA, essential for aerobic chemotaxis.
• The conditional activity of McpA suggests a sophisticated sensory system in R. sphaeroides, likely involving multiple MCPs responding to different environmental cues.
• The findings indicate that R. sphaeroides employs a diverse array of MCPs to adapt its chemotactic behavior to varying environmental conditions.