A putative MerR family regulator involved in biofilm formation in Listeria monocytogenes 4b G.

The capability of forming biofilm makes the foodborne pathogen Listeria monocytogenes more resistant to environmental stresses. To examine the mechanism of biofilm formation, L. monocytogenes transposon mutant strain GB8 with decreased ability to form biofilm was characterized in this study. Southern blot assay revealed a single copy of transposon in the GB8 chromosome, and the insertion site was identified by inverse polymerase chain reaction (IPCR). The expression of lm.G_1497 was found to be inactivated by the transposon insertion, and the gene was identical to gene LMOf2365_1497 in the sequenced strain L. monocytogenes strain 4b F2365, encoding a MerR family protein. The ability of producing biofilm was recovered in revertant GBR8. It was confirmed by quantitative real-time PCR that the transcription of the gene flanking lm.G_1497 was not affected by Tn917 insertion. These results suggested that lm.G_1497 was responsible for the positive regulation of biofilm formation in L. monocytogenes 4b G. Moreover, the failure of lm.G_1497 expression resulted in a decrease of the autolysis rate, while no effect on cell growth and motility in L. monocytogenes GB8, which might imply that the reduction in biofilm was caused by the difference in cell autolysis.