A chemotaxis cluster from Agrobacterium tumefaciens

Area of Science:

• Microbiology
• Molecular Biology
• Genomics

Background:

• Chemotaxis is essential for bacterial survival, enabling directed movement towards attractants or away from repellents.
• Agrobacterium tumefaciens is a plant pathogen known for its genetic transformation capabilities, but its chemotaxis system is not fully understood.

Purpose of the Study:

• To sequence and characterize a novel chemotaxis operon in Agrobacterium tumefaciens.
• To identify the genes within the operon and their potential roles in chemotaxis.

Main Methods:

• DNA sequencing of a 9.6-kb chromosomal region.
• Bioinformatic analysis to identify open reading frames (ORFs) and predict protein functions.
• Gene disruption (mutagenesis) to assess the functional impact of specific genes on chemotaxis.
• PCR and heterologous probing to locate genes absent from the sequenced region.

Main Results:

• A putative 8-kb chemotaxis operon was identified, containing genes homologous to known chemotaxis proteins (MCPs, CheY, CheA, CheR, CheB).
• The operon's gene arrangement is conserved compared to other bacteria like Sinorhizobium meliloti and Rhodobacter sphaeroides.
• Mutations in orf1 and cheA impaired chemotaxis, confirming their roles.
• Deletion of orf10 did not affect chemotaxis or motility.
• The cheW gene was located elsewhere in the genome, as it was absent from this operon.

Conclusions:

• A novel chemotaxis operon in Agrobacterium tumefaciens has been characterized, providing insights into bacterial sensory mechanisms.
• The identified genes, particularly orf1 and cheA, are essential for chemotaxis in this bacterium.
• The absence of cheW within this operon suggests a unique genomic organization of chemotaxis genes in Agrobacterium tumefaciens.