Hydrodynamic instabilities in self-signalling auto-chemotactic active suspensions*

Chemotaxis is the phenomenon by which active swimmers migrate towards regions of higher chemical concentration, a feature that is crucial to their survival. Swimmers such as E. coli are capable of generating their own attractant which gives rise to self-signaling among active swimmers in a suspension. Experiments (Budrene & Berg 1991, 1995) and theories (Brenner et al. 44 (1998), Keller & Segel (1970)) involving auto-chemotactic suspensions of swimmers have shown the creation of instabilities in these systems, resulting in a clustering of these swimmers. This work explores the role of active-stress driven fluid motion, arising from the motility of the swimmers, on the creation of instabilities in auto-chemotactic suspensions of pushers and pullers.