Species-specific surface dwell times and accumulation of microbes investigated by holographic microscopy

Microscopic swimmers, such as bacteria and archaea, are paradigmatic examples of active matter systems. The study of these systems has given rise to novel concepts such as rectification of bacterial swimmers, in which microstructures can passively separate swimmers from non-swimming, inert particles. Many bacteria and archaea swim using rotary molecular motors to drive helical propellers called flagella or archaella. The arrangement of these filaments around the cell body varies between species, yielding a range of swimming patterns. Solid boundaries might affect these swimming patterns in different ways, limiting the generality of artificial rectification devices. We performed three-dimensional cell tracking on four species of bacteria with different flagellation patterns (Escherichia coli, Salmonella enterica, Campylobacter jejuni and Shewanella putrefaciens), and compared these to two environmental isolates of archaea, previously identified with the genera Haloarcula and Haloferax. Despite differences in the cells' flagellation patterns, swimming speeds and swimming patterns, we find that the shapes of cell tracks as individuals leave surfaces are surprisingly consistent. This information reduces the potential parameter space for the design of artificial rectification devices, and increases the possibility of constructing a multi-species bacterial rectifier.This article is part of the theme issue 'Biological fluid dynamics: emerging directions'.