Abstract

An optical trapping technique is implemented to investigate the chemotactic behavior of a marine bacterial strain Vibrio alginolyticus. The technique takes the advantage that the bacterium has only a single polar flagellum, which can rotate either in the counter-clock-wise or clock-wise direction. The two rotation states of the motor can be readily and instantaneously resolved in the optical trap, allowing the flagellar motor switching rate to be measured under different chemical stimulations. In this paper the focus will be on the bacterial response to an impulsive change of chemoattractant serine. Despite different propulsion apparati and motility patterns, cells of V. alginolyticus apparently use a similar response as Escherichia coli to regulate their chemotactic behavior. Specifically, we found that the switching rate of the bacterial motor exhibits a biphasic behavior, showing a fast initial response followed by a slow relaxation to the steady-state switching rate . The measured can be mimicked by a model that has been recently proposed for chemotaxis in E. coli. The similarity in the response to the brief chemical stimulation in these two different bacteria is striking, suggesting that the biphasic response may be evolutionarily conserved. This study also demonstrated that optical tweezers can be a useful tool for chemotaxis studies and should be applicable to other polarly flagellated bacteria.

Highlights

  • Microorganisms face many challenges in their natural habitats, and they develop different strategies to adapt to the environment they live in

  • Another significant difference between the two bacteria is that V. alginolyticus possesses only a single polar flagellum when it is grown in a liquid medium

  • Waves due to flagellar rotation propagate along the cell body, causing its center of mass position (x(t), y(t)) to fluctuate, which can be interrogated using a two-dimensional position sensitive detector (PSD)

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Summary

Introduction

Microorganisms face many challenges in their natural habitats, and they develop different strategies to adapt to the environment they live in. In this study we report new findings of bacterial chemotaxis of Vibrio alginolyticus This bacterium lives in the ocean, but it has much in common with E. coli such as its physical size and its motility being powered by rotary motors. Unlike E. coli, the flagellar motor of V. alginolyticus is more powerful, which can rotate at an angular frequency of a few kilohertz, pushing the cell body at a speed *200 mm=s [1] These values are nearly ten times of those typically seen in E. coli [2,3], reflecting the different ecosystems the two bacteria inhabit. Another significant difference between the two bacteria is that V. alginolyticus possesses only a single polar flagellum when it is grown in a liquid medium This suggests that forward and backward swimming paths are time-reversal symmetric when the motor reverses its direction [4]. In the light of these physiological differences (polar vs. peritrichous flagellation) and their varied motility patterns, one wonders if there is a difference in the way the flagellar motor is regulated by the internal chemotaxis network

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