Enhanced bacterial chemotaxis in confined microchannels: Optimal performance in lane widths matching circular swimming radius

Understanding bacterial behavior in confined environments is crucial for elucidating microbial ecology and developing strategies to manage bacterial infections. While extensive research has focused on bacterial motility on surfaces and in porous media, chemotaxis in confined spaces remains poorly understood. Here, we investigate the chemotaxis of Escherichia coli within microfluidic lanes under a linear concentration gradient of L-aspartate. We demonstrate that E. coli exhibits significantly enhanced chemotaxis in lanes with sidewalls compared to open surfaces, primarily due to cells aligning and swimming along the right sidewalls. By varying lane widths, we identify that an 8 μm width—approximating the radius of bacterial circular swimming on surfaces—maximizes chemotactic drift velocity. These results are supported by both experimental observations and stochastic simulations, establishing a clear proportional relationship between optimal lane width and the radius of bacterial circular swimming. Further geometric analysis provides an intuitive understanding of this phenomenon. Our results offer new insights into bacterial navigation in complex biological environments such as host tissues and biofilms, shedding light on microbial ecology in confined habitats and suggesting new avenues for controlling bacterial infections.