(229n) motB Is Involved in the Response of Escherichia coli to Material Stiffness during Biofilm Formation

Bacterial biofilm formation is a leading cause of chronic infections, which lead to nearly 100,000 deaths and 28-45 billion dollars of cost each year in the U.S. alone. The chemical and physical properties of substratum surfaces play important roles in biofilm formation. We recently reported that the stiffness of poly(dimethylsiloxane) (PDMS) affects bacterial adhesion and the physiology of attached cells. In this study, the automated contour-based tracking package for in vitro environment (ACTIVE) developed in the Henderson Lab was validated for tracking bacterial cells. By comparing the motility of attached Escherichia coli cells on PDMS surfaces with different Youngâ??s moduli (0.1 MPa for soft and 2.6 MPa for stiff) using ACTIVE, the attached cells were found to be more mobile on stiff surfaces during the early stage of biofilm formation than those on soft surfaces. To further investigate if motility is important to bacterial response to material stiffness, Escherichia coli RP437 and its isogenic mutants of motility (motB), flagella (fliC) and type I fimbriae (fimA) were compared for adhesion on soft and stiff PDMS. The motB mutant exhibited defects in response to PDMS stiffness (based on cell counting and tracking with ACTIVE), which was recovered by complementing the motB gene on a plasmid. In comparison, mutation of fliC and fimA did not show significant effect. Collectively, the findings from this study suggest that Escherichia coli cells can actively respond to material stiffness during biofilm formaiton, and motB is involved in such response.