Abstract
ABSTRACT Background Streptococcus mutans, a biofilm-forming bacterium, possesses several transporters that function as import/export molecules. Among them, the PII protein family is composed of members that regulate glutamine synthesis in bacterial species. Objective In this study, we characterized the function of the glutamine transporter in S. mutans MT8148. Methods The SMU.732 gene, corresponding to glnP in S. mutans, is homologous to the glutamine transporter gene in Bacillus subtilis. We constructed a glnP-inactivated mutant strain (GEMR) and a complement strain (comp-GEMR) and evaluated their biological functions. Results Growth of GEMR was similar in the presence and absence of glutamine, whereas the growth rates of MT8148 and comp-GEMR were significantly lower in the presence of glutamine as compared to its absence. Furthermore, biofilms formed by MT8148 and comp-GEMR were significantly thicker than that formed by GEMR, while the GEMR strain showed a significantly lower survival rate in an acidic environment than the other strains. Addition of n-phenyl-2-naphthylamine, used to label of the membrane, led to increased fluorescence intensity of MT8148 and GEMR, albeit that was significantly lower in the latter. Conclusions These results suggest that glnP is associated with glutamine transport in S. mutans, especially the import of glutamine involved in biofilm formation.
Highlights
A previous genomic analysis of Streptococcus mutans predicted four putative glutamine uptake systems, one of which is known to be associated with glnP [1]
According to our eva luation of confocal laser scanning microscopy (CLSM) images, biofilms formed by MT8148 and comp-glnP-inactivated mutant strain (GEMR) were thicker than those formed by GEMR, while GEMR biofilms showed both small and large amorphous micro-colonies (Figure 3(a))
The biofilm mass formed by GEMR was less than that formed by MT8148 and comp-GEMR, which was supported by the results of quantitative assays (Figure 3(b))
Summary
A previous genomic analysis of Streptococcus mutans predicted four putative glutamine uptake systems, one of which is known to be associated with glnP [1]. S. mutans, a Gram-positive facultative anaero bic bacterium, is considered to be a major etiolo gic agent of human dental caries and reported to form biofilm known as dental plaque on tooth surfaces [12]. This organism possesses several transport proteins in the cell membrane for export and import of molecules [13]. Methods: The SMU.732 gene, corresponding to glnP in S. mutans, is homologous to the glutamine transporter gene in Bacillus subtilis. Conclusions: These results suggest that glnP is associated with glutamine transport in S. mutans, especially the import of glutamine involved in biofilm formation
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