Biophysical Thresholds for Biofilm Formation and Dispersal

Abstract

Bacteria exist in virtually every domain, from organic domains such as our bodies and the natural environment, to inorganic domains such as industrial plant systems. To survive in these diverse and complex settings, bacteria alternate between two physiological states: the unicellular, free-swimming planktonic state and the multicellular, surface-attached biofilm state. Since the physiological state of bacteria critically influences process outcomes in medicine, agriculture, industry, and environment, much effort has been made to predict and control bacterial state transitions. Unfortunately, such efforts are challenged by the multitude of regulatory factors, from bacterial properties to environmental and initial conditions. To address this challenge, previous work in the Datta Lab has developed a generally-applicable mathematical model of the planktonic-to-biofilm transition under positive quorum sensing control and established key principles governing biofilm formation. Building on previous work, this thesis modifies and extends the established model to explore two cases: negative quorum sensing control, exhibited by Vibrio cholerae, and positive quorum sensing control with reversible transition between planktonic and biofilm states, characteristic of many bacteria. For both cases, I established two dimensionless parameters that capture the competing forces of autoinducer production, diffusion, and binding to bacterial receptors. Based on known properties and initial conditions, the parameters predict the extent of biofilm formation and dispersal. My work furthers the established theoretical foundation and provides quantitative guidance for predicting and controlling biofilm formation and dispersal in diverse and complex settings.