Do cyanobacteria swim using travelling waves?

Richard Montgomery, UCSC

We (Kurt Ehlers and myself) are investigating a ``mystery swimmer'' -- the cyanobacterium (previously known as blue-green algae) Synechococcus. This organism is prevalent in the mid-Atlantic, and may be crucial to the carbon cycle. It swims at speeds of up to 25 $\mu m/s$ in seawater and is a rod shaped organism, approximately 1 $\mu $ in diameter and roughly twice that in length. No one knows how (or why)it swims! It has no flagella, either external or internal. It has been observed with resolutions of .2 $\mu$ and within this resolution no change of shape has been observed.

We propose a thrust mechanism consisting of small amplitude high frequency waves travelling along the cell membrane. The travelling waves consist of surface oscillations. which may be tangential to the surface and still yield the observed speeds.

I will begin by reviewing the basic theory which was developed by Brennen, Blake, and others, and added to by Shapere and Wilczek. This is low Reynolds number fluid mechanics coupled with a small amplitude approximation and a bit of gauge theory. We will then describe the basic result, and perhaps suggest future directions and applications.