Effects of non-ionic solute stresses on biofilm formation and lipopolysaccharide production in Escherichia coli O157:H7

The addition of non-ionic solutes such as sucrose and polyethylene glycol (PEG) to a culture of Escherichia coli O157:H7 stimulated formation of a biofilm on an abiotic surface. Possible factors involved in this increased biofilm formation were evaluated, i.e. oxidative stress, exopolysaccharide (EPS) production, membrane composition and lipopolysaccharide (LPS) production. A green fluorescent protein (GFP)-based reporter strain, anaerobic experiment and microarray data suggested that the increased biofilm formation was not due to oxidative stress. Quantification of the EPS revealed that cell-released EPS production appeared not to be related. Bacterial results of fatty acid methyl ester (FAME) analysis, along with microarray data, showed that sucrose and PEG could induce membrane rigidity via alterations in the fatty acid (FA) composition. Based on transcriptome analysis, PEG was observed to induce several membrane-related genes and membrane-associated LPS synthesis genes, confirmed by quantitative real-time RT-PCR analysis. Interestingly, biofilm cells showed higher expression than planktonic cells of ompC (encoding an outer membrane protein) and many LPS- and polysaccharide-related genes (glmS, dxs, msbB and kdsA genes) when subjected to PEG treatment. Greater LPS production could be observed under both PEG and sucrose-added biofilm conditions in E. coli O157:H7. Our data suggest that sucrose and PEG resulted in biofilm formation of E. coli O157:H7, not as a result of oxidative stress and EPS production, but via increases in membrane rigidity and LPS production.