Bacteria behavior in vortical flows*

The Hawaiian Bobtail Squid has an internal ciliated organ that recruits a single beneficial bacterial species, V. fischeri, against a large background of other bacterial species and particles suspended in the ambient water. How is this specificity achieved? We have recently shown that the ciliary beat generates a vortical flow field acting like a hydrodynamic sieve and preferentially accumulating bacteria-sized particles whereas larger particulate tends to be rejected. However, it is unknown whether, in addition to particle size, other properties, such as particle shape or behavioral response, contribute to the hydrodynamic pre-selection of candidate bacteria. It is experimentally very challenging to investigate these questions in the living squid. Hence, we have developed a microfluidic system that mimics the ciliary flow patterns. Here, we examine how inanimate particles and V. fischeri with different behavioral properties  interact with the biomimetic vortical flow field to reveal additional selection criteria imposed by the ciliary currents.