Abstract

Many microorganisms have evolved the ability to swim and bias their swimming to find nutrients and favourable conditions for growth. For example, several species of swimming bacteria from all environments (aquatic, intestinal, rhizobial, ...) can efficiently move up gradients of chemical attractants. Swimming algae can also get themselves to optimally lit environs by phototaxis (a benefit for phototrophs!). As a postdoc, I have studied the biophysics of such swimming biases, focusing on population-scale behaviour. At this scale unexpected phenomena emerge from the biased swimming of individual cells. For example, suspensions of bottom-heavy biflagellate algae (e.g. Chlamydomonas or Dunaliella) are unstable, breaking up into beautiful patterns. I will introduce how the biophysics in terms of which these phenomena can be explained and modelled. Then I will present my results on the dispersion of bacteria in porous gels and of algal suspensions flowed in a pipe. Finally, I will talk about my current research on the role biased swimming plays in algal-bacterial symbioses and in the design of efficient algal bioreactors.