FliA-Dependent Surface Macromolecules Promote Initial Biofilm Development of Escherichia coli by Influencing the Bacterial Surface Properties

Abstract

FliA is an important regulatory component for the synthesis 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, sur- face heterogeneity and surface roughness, and initial biofilm development consisting of re- versible 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 re- versible adhesion and auto-adhesion capacities of wild-type cells were higher than the mu- tant 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 cells to Si3N4 in water was at least 2.0-fold greater than that of the mutants due to signifi- cantly 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.