Roles of ionic strength and biofilm roughness on adhesion kinetics of Escherichia coli onto groundwater biofilm grown on PVC surfaces

Mechanisms of Escherichia coli attachment on biofilms grown on PVC coupons wereinvestigated. Biofilms were grown in CDC reactors using groundwater as feed solution overa period up to 27 weeks. Biofilm physical structure was characterized at the micro- andmeso-scales using Scanning Electron Microscopy (SEM) and Optical Coherence Tomography(OCT), respectively. Microbial community diversity was analyzed with TerminalRestricted Fragment Length Polymorphism (T-RFLP). Both physical structure and microbialcommunity diversity of the biofilms were shown to be changing from 2 weeks to 14 weeks,and became relatively stable after 16 weeks. A parallel plate flow chamber coupled with aninverted fluorescent microscope was also used to monitor the attachment of fluorescentmicrospheres and E. coli on clean PVC surfaces and biofilms grown on PVC surfaces fordifferent ages. Two mechanisms of E. coli attachment were identified. The adhesion ratecoefficients (kd) of E. coli on nascent PVC surfaces and 2-week biofilms increased with ionicstrength. However, after biofilms grew for 8 weeks, the adhesion was found to be independentof solution chemistry. Instead, a positive correlation between kd and biofilmroughness as determined by OCT was obtained, indicating that the physical structure ofbiofilms could play an important role in facilitating the adhesion of E. coli cells.