SMU.746-SMU.747, a Putative Membrane Permease Complex, Is Involved in Aciduricity, Acidogenesis, and Biofilm Formation in Streptococcus mutans

Abstract

Dental caries induced by Streptococcus mutans is one of the most prevalent chronic infectious diseases worldwide. The pathogenicity of S. mutans relies on the bacterium's ability to colonize tooth surfaces and survive a strongly acidic environment. We performed an ISS1 transposon mutagenesis to screen for acid-sensitive mutants of S. mutans and identified an SMU.746-SMU.747 gene cluster that is needed for aciduricity. SMU.746 and SMU.747 appear to be organized in an operon and encode a putative membrane-associated permease. SMU.746-and SMU.747-deficient mutants showed a reduced ability to grow in acidified medium. However, the short-term or long-term acid survival capacity and F 1 F 0 ATPase activity remained unaffected in the mutants. Furthermore, deletion of both genes did not change cell membrane permeability and the oxidative and heat stress responses. Growth was severely affected even with slight acidification of the defined medium (pH 6.5). The ability of the mutant strain to acidify the defined medium during growth in the presence of glucose and sucrose was significantly reduced, although the glycolysis rate was only slightly affected. Surprisingly, deletion of the SMU.746-SMU.747 genes triggered increased biofilm formation in low-pH medium. The observed effects were more striking in a chemically defined medium. We speculate that the SMU.746-SMU.747 complex is responsible for amino acid transport, and we discuss its possible role in colonization and survival in the oral environment.

Identification of an Efflux Transporter LmrB Regulating Stress Response and Extracellular Polysaccharide Synthesis in Streptococcus mutans

“…Similarly, enhanced EPS production was noticed in S. mutans biofilm upon lmrB inactivation. The observed enhanced biofilm formation phenotypes of lmrB mutant cannot be caused by polar effect of mutations based on the observation that lmrB was a separate transcription unit ( Krol et al, 2014 ), which was in consistent with the notion that MFS members function as single-component pumps in Gram-positive bacteria ( Li and Nikaido, 2004 ). Therefore, it is intriguing how lmrB deletion affected the EPS production?…”

Acid‐adaptive mechanisms of Streptococcus mutans–the more we know, the more we don't

“…Transcription of ilvE is modulated by the global regulators CcpA and CodY (Santiago et al ., ). A recent study also indicated that the putative amino acid transporter encoded by SMU.745/SMU.746 was important for growth of S. mutans in acidified media, further indicating a role for amino acid metabolism in acid tolerance (Krol et al ., ).…”

Genome-wide discovery of novel M1T1 group A streptococcal determinants important for fitness and virulence during soft-tissue infection

“…mutans , a transposon screen found that the homologs SMU.746 ( scfA ) and SMU.747 ( scfB ) were important for the acid stress response and biofilm formation [ 51 ]. Although the authors hypothesized that the genes encoded for an amino acid permease, that was not demonstrated [ 51 ]. In B .…”