  Marine bacterium Vibrio alginolyticus uses a single polar flagellum to
navigate in an aqueous environment. Similar to Escherichia coli cells, the
polar flagellar motor has two states; when the motor is counter-clockwise, the
cell swims forward and when the motor is clockwise, the cell swims backward. V.
alginolyticus also incorporates a direction randomization step at the start of
the forward swimming interval by flicking its flagellum. To gain an
understanding on how the polar flagellar motor switch is regulated,
distributions of the forward $\Delta_{f}$ and backward $\Delta_{b}$ intervals
are investigated herein. We found that the steady-state probability density
functions, $P(\Delta_{f})$ and $P(\Delta_{b})$, of freely swimming bacteria are
strongly peaked at a finite time, suggesting that the motor switch is not
Poissonian. The short-time inhibition is sufficiently strong and long lasting,
i.e., several hundred milliseconds for both intervals, which is readily
observed and characterized. Treating motor reversal dynamics as a first-passage
problem, which results from conformation fluctuations of the motor switch, we
calculated $P(\Delta_{f})$ and $P(\Delta_{b})$ and found good agreement with
the measurements.
