I am interested in swimming microorganisms, in particular microscopic bacteria (e.g. soil rhizobia) and algae (e.g. ocean phytoplankton). My research focuses on the new physics required to understand these swimmming microorganisms, from single cells to populations. Unlike passive microscopic particles (e.g. colloids), swimmers self-propel and actively respond to environmental bias (gravity, flow, light, chemicals...). Thus, swimmers suspensions often behave in a markedly distinct way from ordinary colloidal suspensions. A classical example is bioconvection, spontaneous large scale convection in shallow layers of swimmer supsensions (without a vertical temperature gradient, as in classical Rayleigh–Bénard convection). Typical environments for my swimmers are tubes, channels and porous media, as inspired by current problems in sustainable bioengineering and environmental microbiology.

The new physics of swimmers has the potential to improve promising bioengineering applications. My research centers around two such appplications: (1) removing pollutants from soil using bacteria (bioremediation) (2) growing algae in ponds and tubes for their products (photobioreactors). I use a combination of mathematical modelling and experiments to solve problems inspired by these applications, such as the growth dynamics of gyrotactic swimming algae in air-lift photobioreactors.

Aside from bioengineering applications, I am also very interested in how biophysics can contribute to enviromental microbiology, in particular the roles of swimming and metabolite diffusion in the symbiosis between algae and bacteria. Again, these problems are tackled theoretically and experimentally.

I am affiliated with the Biological and Soft Systems Sector (BSS) in the Cavendish Laboratory (Department of Physics). Within Cambridge University I also collaborate closely with the Deparments of Plant Sciences (Prof Alison Smith's group), Engineering (Dr Stuart Scott's group) and Department for Applied Mathematics and Theoretical Physics (Prof Ray Goldstein's group).