ABC transporter activities in biofilm formation by Streptococcus mutans

Abstract: ObjectiveStreptococcus mutans, a biofilm forming bacterium, has been found to possess over 60 ATP-binding cassette (ABC) transporters in gene analysis. ABC transporters have important functions related to gathering nutrients and exporting unnecessary materials, and are considered to be involved in biofilm formation by S. mutans. In the present study, we identified ABC transporter-related biofilm formation by the bacterium and analyzed related functions.MethodsInformation regarding the SMU1520 gene encoding ABC membrane transporters possibly associated with biofilm formation was extracted from a database containing the entire amino acid sequence of the S. mutans UA159 strain. To investigate the role of SMU1520, we constructed an SMU1520-deletion mutant strain (Δ1520 ) of S. mutans MT8148. The upstream region of SMU1520, an erythromycin cassette gene, and the downstream region were amplified by PCR using specific primers, then those three products were combined and transformed into S. mutans MT8148 using a double-crossover recombination method to construct Δ1520. To examine bacterial growth, MT8148 and Δ1520 were grown for 18 hours at 37°C, then inoculated into fresh Todd Hewitt broth at 37°C. Absorbance at 600 nm was measured every 1 hour using a spectrophotometer. Assays of biofilm formation by MT8148 and Δ1520 were then performed, and biofilm structures were observed using confocal laser scanning microscopy (CLSM).ResultsThe growth rate of Δ1520 was slightly lower than that of MT8148. Furthermore, the quantity of biofilm formed by Δ1520 was significantly decreased, with a reduction rate of 55%. Additionally, CLSM results demonstrated that biofilm formed by Δ1520 was more coarse as compared to that formed by MT8148.ConclusionThe present results suggest that SMU1520 contributes to bacterial growth and biofilm formation by involving export/import molecules. This study was supported by JSPS KAKENHI grants (20K18757).