Bacterial biofilms have garnered much attention in recent years due to their importance in a wide range of both natural and engineered processes such as infection, water treatment, food processing, and oil pipelining. Here, we use a microfluidic device to quantify the effects of fluid shear force on the biofilm morphology of Shewanella oneidensis, a metal reducing bacteria of interest for several bioremediation and energy applications.

For different rates of fluid flow through a microfluidic channel, the time evolution dynamics of biofilms were studied, and we quantified several evolutionary features in the morphology, such as cluster size, cluster distribution, surface coverage, and pattern anisotropy. We found that low flow rates resulted in significant clumping of cells, intermediate flow rates resulted in smoothly distributed biofilms, and intermediate flow rates maximized the rate of surface coverage. Furthermore, to develop a deeper understanding of biofilm characteristics such as the distribution of extracellular polymeric substances (EPS), we have acquired AFM images of biofilms after a day of growth at different flow rates. Previously, Richter et al. evaluated colony expansion of Candida albicans in a microfluidic device with and without flow, Lee et al. reported limited vertical growth and elongated horizontal growth of Staphylococcus epidermidis biofilms in response to high shear forces, and De La Fuente et al. characterized adhesion for a range of Xylella fastidiosa flow rates. However, our study is unique in that we present a single-cell level quantification of the evolutionary dynamics of S. oneidensis biofilm formation at several different fluid flow rates.

For this characterization, we have fabricated microfluidic devices, which was used for flowing cell culture different rates to allow biofilm growth. Images were captured every 10 minutes using a Zeiss Axioplan 2 epifluorescent microscope fitted with an incubation chamber set at 30°C; Following 24 hours of incubation, the samples were frozen, followed by imaging using atomic force microscopy. AFM images revealed in tact flagella on the cells which were exposed to low shear forces.Quantitative characterization of S. oneidensis biofilm formation guides further investigations into the precise mechanisms dictating the observed morphologies and contributes to future efforts to harness these bacteria for bioremediation and energy applications.