Functional characterization of cell-wall-associated protein WapA in Streptococcus mutans

Abstract

Streptococcus mutansis known as a primary pathogen responsible for dental caries. One of the virulence factors ofS. mutansin cariogenicity is its ability to attach to the tooth surface and form a biofilm. Several surface proteins have been shown to be involved in this process. A 29 kDa surface protein named wall-associated protein A (WapA, antigen A or antigen III), was previously used as a vaccine in animal studies for immunization against dental caries. However, the function of WapA inS. mutansis still not clear. This study characterized the function of WapA in cell surface structure and biofilm formation. Compared to the wild-type, thewapAmutant had much-reduced cell chain length, diminished cell–cell aggregation, altered cell surface ultrastructure, and unstructured biofilm architecture. Furthermore,in vivoforce spectroscopy revealed that the cell surface of thewapAmutant was less sticky than that of the wild-type cells. More interestingly, these phenotypic differences diminished as sucrose concentration in the medium was increased to 0.5 %. Real-time RT-PCR analysis demonstrated that sucrose strongly repressedwapAgene expression in both planktonic and biofilm cells. These results suggest that the WapA protein plays an important structural role on the cell surface, which ultimately affects sucrose-independent cell–cell aggregation and biofilm architecture.