FliA is an important regulatory component for the synthesis Trivets of surface macromolecules which are involved in motility and biofilm development of Escherichia coli.In this study, the roles of FliA-dependent surface macromolecules in E.coli surface tension, surface heterogeneity and surface roughness, and initial biofilm development consisting of reversible and irreversible adhesion were investigated using E.coli MG1655 wild-type strain and fliA gene deleted mutant strain.Negative Gibbs free energy change values calculated using bacterial surface tensions obtained by a spectrophotometric method showed that both wild-type and mutant cells in water can reversibly adhere to the surface of the model solid, silicon nitride (Si3N4).
The calculations further showed that bacterial reversible auto-adhesion and co-adhesion were also thermodynamically favorable.In comparison, the reversible adhesion and auto-adhesion capacities of wild-type cells were higher than the mutant cells.Direct measurements by atomic force microscopy (AFM) and thorough analysis of the recorded adhesion data showed that the irreversible adhesion strength of wild-type Evening gowns cells to Si3N4 in water was at least 2.0-fold greater than that of the mutants due to significantly higher surface heterogeneity resulting in higher surface roughness for the wild-type cells compared to those obtained for the mutants.These results suggest that strategies aimed at preventing E.
coli biofilm development should also consider a combined method, such as modifying the surface of interest with a bacterial repellent layer and targeting the FliA and FliA-dependent surface macromolecules to reduce both reversible and irreversible bacterial adhesion and hence the initial biofilm development of E.coli.