Investigation of expressions of biofilm-related genes in porin protein mutants of Escherichia coli W3110

Biofilm formation is a comprehensive and multicellular formation involving many different mechanisms and regulatory genes. This formation is affected by many factors such as nutrient availability, temperature, humidity, and pH. In this study, changes in the expression levels of genes involved in biofilm formation were investigated in ompA, ompC, and lamB porin mutants, which are outer membrane proteins of Escherichia coli. The wild-type E. coli W3110 strain we used in our study and the phoE mutant of this strain did not form biofilms under any of the conditions we tried, but ompA and ompC mutants of this strain formed biofilms at pH 6, 7, and 8, while the lamB mutant only formed biofilm at pH 7. To elucidate the biofilm mechanism in mutants, changes in the expression levels of biofilm-associated genes (csgD, csrA, rcsB, pgaC, qseB, qseC, sdiA) of wild-type E. coli W3110 and porin mutants grew at pH 6.7 and 8 were investigated. Accordingly, it was determined that csrA and rcsB genes decreased in ompA and ompC mutants at every pH value studied, while csgD, pgaC, and sdiA genes increased compared to wild-type. Also, in ompA and ompC mutants, the regulators of flagellar genes qseB and qseC decreased at other pHs except pH 6. While the qseB gene increased slightly in both mutants at pH 6, the qseC gene increased in the ompA mutant and decreased in the ompC mutant. The overexpression of qseB and qseC genes, whose overexpression may negatively affect biofilm formation, slightly increased at pH 6, resulting in a slight decrease in biofilm formation in ompA and ompC porin mutants than at pH 7 and 8. It was determined that in the lamB mutant, which gave similar gene expressions with other mutants at pH 7, the qseBC genes were overexpressed at pH 6 and the csgD gene was underexpressed at pH 8. These conditions were determined to inhibit biofilm formation in the lamB mutant. In line with the obtained expression data, opinions about the mechanisms that lead mutants to biofilm formation were put forward. According to these views, it was determined that the expression of biofilm-related genes increased and decreased in the biofilm formation of ompA, ompC, and lamB mutants by biofilm formation. However, from these data, no information has yet been obtained about how the mutant porins induce biofilm formation.