Single-cell imaging of motile and sessile microbial communities across different scales

Bacteria in nature live in two alternating lifestyles: a free-swimming, planktonic state to search for food, and a sessile, biofilm state to adhere to nutritious surfaces. Currently, these two states are studied by separate research communities, hampering our understanding on how these two populations interact and how they interconvert from one to the other. The major technical obstacle is the lack of imaging tools to simultaneously capture the dynamics of both populations. In this talk, I will talk about our ongoing effort in combining single-cell resolution confocal imaging with high-speed three-dimensional digital in-line holography (DIH) to generate a unique cost-effective setup, dubbed HoloCon, for visualizing and quantifying both the sessile and motile populations in one single setup in real time. Using this setup, we revealed the mechanism underlying how resident biofilms repel free-swimming cells attempting to colonize and invade the biofilm, a common scenario in microbial ecology. We have also used HoloCon to study the reverse problem of how biofilm-dwelling cells disperse and swim away from an existing biofilm. The new instrumentation we propose will also be of great use to researchers interested in observing the collective dynamics of bacterial cells at high spatiotemporal resolution.