Influence of Shear Stress, Flow Fluctuations, and Cell Motility on Biofilm Formation

Biofilms contribute to pathogenic contamination of drinking water, biofilm-related diseases, sediment erosion rates, and wastewater treatment. In this talk, I will discuss how physical factors, specifically hydrodynamic conditions, flow fluctuations, and bacterial motility, influence biofilm development, focusing on Pseudomonas putida and Pseudomonas aeruginosa.



First, I will cover how hydrodynamic conditions and microscale surface roughness control early-stage Pseudomonas putida biofilm growth. Microfluidic experiments and numerical simulations show that high flow conditions suppress biofilm growth, with a critical local velocity for development around 50 μm/s, matching P. putida's swimming speed. Surface roughness enhances early biofilm formation by increasing low-flow areas. The critical shear stress for development on rough surfaces is 0.9 Pa, compared to 0.3 Pa on smooth surfaces.



Next, I will discuss how flow fluctuations impact Pseudomonas putida biofilm growth. While most research focuses on steady flows, fluctuations are common in natural and engineered systems. Our experiments indicate that biofilm growth under fluctuating conditions follows a three-phase process (lag, exponential, fluctuation) versus a four-phase model in steady flow. Low-frequency fluctuations promote growth, whereas high-frequency fluctuations inhibit it, as an adjustment time is needed for biofilm regrowth when flow conditions change. We propose a theoretical model explaining these patterns and providing management strategies for biofilm growth under fluctuating flows.



Finally, I will address how bacterial cell motility affects Pseudomonas aeruginosa biofilm development. Our microfluidic experiments reveal that motility enhances biofilm formation by orienting cells toward surfaces, increasing attachment and density. We propose a theoretical model predicting cell orientation based on local flow velocity and swimming speed, indicating that motility can enhance biofilm density by up to tenfold. Our findings highlight the role of motility in biofilm formation and offer strategies for managing biofilms in environmental and medical contexts.