Department of Physics and Astronomy, University of Pittsburgh, 3941 O'Hara Street, Pittsburgh, PA 15260, USA.
Proc Natl Acad Sci U S A. 2011 Feb 8;108(6):2246-51. doi: 10.1073/pnas.1011953108. Epub 2011 Jan 4.
We investigate swimming and chemotactic behaviors of the polarly flagellated marine bacteria Vibrio alginolyticus in an aqueous medium. Our observations show that V. alginolyticus execute a cyclic, three-step (forward, reverse, and flick) swimming pattern that is distinctively different from the run-tumble pattern adopted by Escherichia coli. Specifically, the bacterium backtracks its forward swimming path when the motor reverses. However, upon resuming forward swimming, the flagellum flicks and a new swimming direction is selected at random. In a chemically homogeneous medium (no attractant or repellent), the consecutive forward t(f) and backward t(b) swimming times are uncorrelated. Interestingly, although t(f) and t(b) are not distributed in a Poissonian fashion, their difference Δt = |t(f) - t(b)| is. Near a point source of attractant, on the other hand, t(f) and t(b) are found to be strongly correlated, and Δt obeys a bimodal distribution. These observations indicate that V. alginolyticus exploit the time-reversal symmetry of forward and backward swimming by using the time difference to regulate their chemotactic behavior. By adopting the three-step cycle, cells of V. alginolyticus are able to quickly respond to a chemical gradient as well as to localize near a point source of attractant.
我们研究了极性鞭毛海洋细菌 V. alginolyticus 在水介质中的游动和趋化行为。我们的观察表明，V. alginolyticus 执行一种循环的、三步（前进、后退和鞭毛摆动）游动模式，与大肠杆菌采用的跑-跌模式明显不同。具体来说，当马达反转时，细菌会回溯其前进的游动路径。然而，当重新开始向前游动时，鞭毛会摆动，随机选择新的游动方向。在化学均匀的介质中（没有趋化剂或排斥剂），连续的向前游动时间 t(f) 和向后游动时间 t(b) 是不相关的。有趣的是，尽管 t(f) 和 t(b) 不是按泊松分布的，但它们的差值 Δt=|t(f)-t(b)|是。另一方面，在趋化剂的点源附近，t(f) 和 t(b) 被发现是强相关的，并且 Δt 服从双峰分布。这些观察表明，V. alginolyticus 通过利用前进和后退游动的时间反转对称性，通过时间差来调节它们的趋化行为。通过采用三步循环，V. alginolyticus 的细胞能够快速响应化学梯度，并在趋化剂的点源附近定位。
