A novel agar-based millifluidic device for spatially-structured microbial populations

The role of spatial structure in microbial ecology and evolution is increasingly recognised and investigated, often with agar plates as a template for a spatially structured environment. While convenient, agar plates do not allow for the spatial and temporal control microbiologists have become accustomed to in the field of microfluidics with its tight environmental control for single cells and small populations, holding back research on surfaces and at larger length scales and population sizes. To close this gap, we developed a novel device with an agar sheet sealing indented channels through which media perfuses. As proof of principle, we grew populations of non-motile Escherichia coli and motile Pseudomonas aeruginosa for 60 hours with continuous propagation of the colonys front, in contrast to agar plates where growth declined much earlier and stopped after about 40 hours. To demonstrate the capabilities of spatial control, we grew P. aeruginosa along different temporally-stable gradients of the cephalosporin antibiotic ceftazidime and characterised the emerging bacterial growth patterns. The device is a step towards highly controlled studies of microbial populations in continuous, non-uniform spatially structured environments. Designed with cost and accessibility in mind, we believe that this novel device will enable new insights into microbial ecology and evolution.