Pseudomonas aeruginosa: a model system for studying the behavior of unbiased flagellar motors

The flagellar motor of Pseudomonas aeruginosa operates in a near-unbiased manner, extending the classical paradigm established by Escherichia coli. Rather than altering rotational bias, P. aeruginosa achieves chemotaxis by symmetrically modulating the dwell times of the two rotational states. This strategy is associated with a mechanically adaptive dual-stator architecture (MotAB and MotCD) and is further modulated by c-di-GMP signaling and auxiliary proteins such as FliL and MotY. At the molecular level, the distinctive reversal behavior is thought to arise from the unique response of the switch complex (located on the rotor) to phosphorylated CheY, which alters switching kinetics rather than rotational bias. These features collectively give rise to distinct swimming behaviors, including a "wrap" state that facilitates three-dimensional reorientation. This system reveals general principles of how molecular machines balance speed, torque, and switching in complex environments.