| dc.description.abstract | Biofilms are aggregated communities of microorganisms, that are involved with up to 80% of all human infections including oral diseases, chronic tissue infections, chronic inflammatory diseases, and acute infections. The biofilm microorganisms are embedded within a matrix consisting of extracellular polymeric substances, where the community interacts through secretion and detection of metabolites. One type of these secreted metabolites called bacteriocins are antimicrobial peptides synthesized on the ribosome, exported through ABC transporters and that inhibit a specific group of microorganisms, often species closely related to the bacteriocin producer. Self-immunity against the bacteriocin is acquired through bacteriocin-immunity proteins, which can act through different mechanisms. The aim of this study was to set up assays to assess the impact of putative bacteriocin-immunity proteins in forming and shaping of biofilms.
By in silico analysis of Streptococcus mutans and Streptococcus sobrinus genomes, a total of nine putative bacteriocin-immunity genes were identified through the bioinformatic tool Bagel4. The suggested genes were mostly bacteriocin-associated ABC transporter genes. A Janus cassette system to generate markerless mutations in S. mutans was set up. Markerless deletion of two putative bacteriocin-immunity genes were achieved. The effects of inactivating the genes were tested through growth curves, crystal violet biofilm staining, and pairwise strain competitions in different biofilm models. The assays demonstrated that deletion of immB [SMU.413] caused reduction in biofilm-formation, in addition individual deletion of either immA [SMU.431] or immB [SMU.413] caused reduction in fitness in the context of either mono-strain cultures or biofilm competitions.
The study demonstrated the use of the Janus cassette system for markerless gene deletions in S. mutans. A biofilm model was set up, which can be used to study bacteriocin interactions of Streptococcus in oral biofilms. A link has been established between SMU.413 and biofilm formation, but the function of the proteins studied here is still unknown. Follow-up studies are needed to test whether they are involved in bacteriocin immunity or other functions as suggested in the discussion. | |
