Cloning and characterization of three cheB genes in Leptospira interrogans

Motility and chemotaxis systems are critical for the virulence of leptospires. There were multiple copies of putative chemotaxis homologs located at leptospires large chromosome. CheB1 and CheB3 from Leptospira interrogans strain Lai are predicted to have a global CheB-like domain, but CheB2 is predicted to have a C-terminal effector domain only. In order to verify the function of three putative cheB genes, they were cloned into pQE31 vector and then expressed, respectively, in wild-type Escherichia coli strain RP437 and cheB defective strain RP4972. The results of swarming assays and the predicted ternary structures of CheB1 and CheB3 of L. interrogans strain Lai suggested that the absence of an N-terminal regulatory domain may be one of the reasons for the failure of CheB2 to complement an E. coli cheB mutant. Furthermore, CheB2 links solely to CheR1 and CheR3 in the interaction network of leptospires. Taken together, these results indicated that CheB2 may not function alone, and under certain physiological conditions, it may require CheB3 and CheR1 to function. The existence of multiple copies of chemotaxis gene homologs suggested that L. interrogans strain Lai might have a more complex chemosensory pathway.