A microfluidic chemotaxis assay to study microbial behavior in diffusing nutrient patches

J.R. Seymour, T. Ahmed, Marcos, R. Stocker
Limnol. Oceanogr. Methods (2008) 6:XXX-XXX

The nutrient environment experienced by planktonic microorganisms is patchy at spatiotemporal scales commensurate with their motility (µm – cm), and the efficiency with which chemotactic microbes can exploit this heterogeneous seascape influences trophodynamics and nutrient cycling rates. Yet, methodological limitations have largely prevented direct examinations of microbial behavior within heterogeneous microenvironments. We used soft lithography to fabricate a microfluidic-based chemotaxis assay to study the foraging response of aquatic microbes to diffusing nutrient patches. A microinjector was used to create a 300 ?m-wide nutrient band, simulating a pulse release of solutes. Chemotactic responses to the diffusing band were measured at the population and single-cell level. This technique permits a real-time assessment of chemotaxis, while detailed information on chemotactic behavior can also be obtained by tracking individual organisms. We applied this assay to study the chemotactic behavior of three marine bacterial isolates, a species of phagotrophic flagellate and a species of phytoplankton. Each organism exhibited rapid chemotactic responses to several compounds, suggesting adaptation to life within patchy microenvironments. This assay is a flexible platform for studying both the specific case of microbes foraging within patchy habitats and as a broadly applicable tool for rapidly assessing and quantifying microbial chemotaxis.