The research in our laboratory is focused on bacterial motility and chemotaxis using the nitrogen-fixing plant symbiont Sinorhizobium meliloti as model organism. Chemotaxis is based on perception and processing of environmental information by receptors and signal transduction via a two-component-system to the flagellar motor. The molecular mechanisms of swimming, chemoreception, and signal transduction differ from the enterobacterial pardigm.
The S. meliloti chemotaxis system utilizes two response regulator proteins, CheY1 and CheY2, but lacks a specific phosphatase. CheY2-P is the dominant regulator of motor response. Its dephosphorylation involves retro-phosphorylation back to the kinase CheA, which in turn phosphorylates free CheY1. S. meliloti exhibits a different type of flagella rotation and hence, swimming mode. While the E. coli motor causes a change of swimming direction by a switch from counter-clockwise to clockwise rotation, the S. meliloti motor rotates exclusively clockwise, but can vary its rotational speed. Changes in the swimming path are caused by an asynchronous deceleration of individual flagella filaments. Rotary speed variation has its molecular corollary in two new motility proteins, MotC and MotE.
