A Novel Streptococcal Glycoprotein Involved in the Biofilm Formation

Biofilm formation is important for bacterial survival and pathogenesis. Oral streptococci display an array of adhesins to mediate the formation of the most complex biofilm, dental plaque. Objectives: This study aims to identify new adhesins from Streptococcus parasanguinis FW213 and determine their function in the biofilm formation. Methods: We searched an unfinished genome of FW213 using in-house blast tool and identified a gene that encodes a cell surface protein; the deduced amino acid sequence was used to predict the function of the protein. Allelic replacement strategy was used to construct a non-polar mutant to determine the ability of the defined mutant to form biofilms. ECL glycoprotein and lectin detection systems were used to examine whether the protein is glycosylated. Results: The FW213 genome has a high-molecular-weight protein (3462-amino-acids) with YSIRK-type signal peptide at the N-terminus and the LPXTG cell-wall-sorting signal at the C-terminus. There are 6 tandem repeat units at the two-thirds of C-terminus, which share limited homology with enterococcal-aggregation-substance like proteins and other cell surface anchor proteins. The insertional mutant exhibited defects in the formation of biofilms on both abiotic and saliva-coated surfaces, thus we named the protein as biofilm-associated protein (BapA). The BapA deficiency led to more severe biofilm defects than the Fap1 deficiency albeit Fap1 has been implicated in the biofilm formation. Inactivation of both bapA and fap1 completely abolished the biofilm formation. The subcellular localization experiments revealed that BapA is associated with cell-wall fractions. The carbohydrate analyses suggested that the BapA protein is modified with N-Acetylglucosmaine-residue containing glycan(s). Conclusion: Our data indicate that BapA is a cell surface glycoprotein and is involved in the biofilm formation. Studies are ongoing to fully characterize the BapA protein and its biological function. This work was supported in part by K22 and R01 grants from NIH/NIDCR.