Séminaire de Mécanique d'Orsay

Le Mardi 13 janvier à 14h00 - Salle de conférences du FAST

Life at low Reynolds number and large Peclet number

Albert Libchaber
Rockefeller University

Some soil microbes use decomposition to get their energy, oxydating sulfur. To increase oxygen flow through water, those microbes apply strong hydrodynamic advection of water, a large Peclet number. The two microbes involved are a Eukariote (a ciliate Uronemella ) and a Prokariote (the bacterium Thiovulum). They both have a fast velocity, close to 0.5 mm/sec, and a comparable size, around 10 µm. Their Reynolds number is still low. They both can tether to boundaries and can produce veils on which they attach. They also store sulfur. Their phenotypes are thus surprisingly comparable; in a given environment nature can evolve different organisms with similar phenotypes! The interaction between the microbes is purely hydrodynamic, each acting as a small vortex and pumping water when they are tethered. The forming veils move at constant velocities and are non-linearly unstable (for Uronemella). It also leads to fascinating bacteria crystal formation and various dynamical system modes when in finite size (for Thiovulum). Those earth microbes shape the world around us, contributing to the soil ecosystem.