Modulating the Stress Response of E. coli at GaN Interfaces Using Surface Charge, Surface Chemistry, and Genetic Mutations

The surface properties of inorganic materials can be used to modulate the response of microorganisms at the interface. We used the persistent photoconductivity properties of chemically treated gallium nitride substrates to evaluate the stress response of wild-type, ΔfliC, and ΔcsgG mutant E. coli exposed to charged surfaces. Substrate surface characterization and biological assays were used to correlate the physiological response to substrate surface charge. The physiological response was evaluated by measuring the intracellular levels of reactive oxygen species (ROS) and Ca²⁺ cations using fluorescent probes. We evaluated the response 1, 2, and 3 h after a short exposure to the surfaces to determine generational effects of the initial exposure on the physiology of the bacteria. In general, the ROS levels 1 h after exposure were not different. However, there were differences in Ca²⁺ levels in E. coli 1 h after the initial exposure to charged GaN surfaces, primarily in the wild-type E. coli. The differences in Ca²⁺ levels depended on the substrate surface chemistry and genetic mutation that suggests the involvement of multiple factors for modulating the interactions of bacteria at interfaces.