Phenotypic, proteomic, and genomic characterization of a putative ABC-transporter permease involved in Listeria monocytogenes biofilm formation.

The foodborne pathogen Listeria monocytogenes is able to form biofilms in food processing environments. Previously, we have reported that an lm.G_1771 gene (encoding a putative ABC-transporter permease) was involved in negative regulation of L. monocytogenes biofilm formation using LM-49, a biofilm-enhanced mutant isolated on Tn917 mutagenesis (AEM 2008 p.7675-7683). Here, the possible action of this ABC-transporter permease in L. monocytogenes biofilm formation was characterized by phenotypic, proteomic, and genomic analyses using an lm.G_1771 gene deletant (Δ1771). The Δ1771 mutant exhibited the same enhanced ability for biofilm formation as the LM-49 strain using a crystal violet staining assay. DNA microarrays and two-dimensional gel electrophoresis revealed 49 and 11 differentially expressed (twofold or more) genes or proteins in Δ1771, respectively. The transcriptomics study indicated that lm.G_1771 could play a vital role in regulating candidate genes involved in biofilm formation such as genes encoding cell surface proteins (Dlt), cell surface anchor proteins (SrtA), and transcriptional regulators (GntR) contributing to negative regulation of biofilm formation by L. monocytogenes. The mutant Δ1771 was more sensitive to Triton X-100 and less resistant to cationic antibiotics, which might be explained by the down-regulation of dlt operon in this deletant and the fact that dlt involves the incorporation of D-alanine residues into lipoteichoic acids, resulting in a positive net charge on the teichoic acids. Therefore, lm.G_1771 is considered to be involved in negative regulation of biofilm formation, and the results from this work provide a possible molecular mechanism of biofilm formation regulated by lm.G_1771 in L. monocytogenes.