On Time Reversal Symmetry and Bacterial Chemotaxis

Motility of polar flagellated bacteria is typically forward and backward in rapid succession. We recently found that one of the marine species, Vibrio alginolyticus, incorporates a flick movement at the end of the backward swimming interval, breaking the time reversal symmetry of the swimming trajectory. A flick in this bacterium is functionally equivalent to a tumble of peritrichously flagellated bacteria, such as Escherichia coli, causing the cell body to deflect in a new direction before the next run starts. Since V. alginolyticus is capable of swimming in both forward and backward directions, it raises an interesting question about how the chemotaxis behavior of this bacterium is regulated. Herein, we provide experimental evidence showing that the marine bacterium differentiates chemical signals detected in the two swimming intervals and responds in the manner that is consistent with the chemotaxis strategy where the forward swimming interval is exploratory and the backward interval is exploitative.