  The formation of bacterial biofilms on solid surfaces within a fluid starts
when bacteria attach to the substrate. Understanding environmental factors
affecting the attachment and the early stages of the biofilm development as
well as the development of active methods of biofilm control are crucial for
many applications. Here we show that biofilm formation is strongly affected by
the hydrodynamics of flows generated by surface waves in layers of bacterial
suspensions. Deterministic wave patterns promote the growth of patterned
biofilms while wave-driven turbulent motion destroys the patterns. The location
of the attached bacteria on a solid substrate differs from the settlement
location of inactive bacteria and of the passive micro-particles: strong
biofilms form under the wave antinodes while passive particles and inactive
bacteria settle under nodal points. By controlling the wave lengths and
horizontal mobility of the wave patterns, one can either shape the biofilm
formation and enhance the biofilm growth, or discourage the formation of
biofilm patterns. The results suggest that the deterministic wave-driven
transport, rather than hydrodynamic forces, determine the preferred location
for the bacterial attachment.
