Dataset Information

Intracellular alpha-amylase of Streptococcus mutans.

ABSTRACT: Sequencing upstream of the Streptococcus mutans gene for a CcpA gene homolog, regM, revealed an open reading frame, named amy, with homology to genes encoding alpha-amylases. The deduced amino acid sequence showed a strong similarity (60% amino acid identity) to the intracellular alpha-amylase of Streptococcus bovis and, in common with this enzyme, lacked a signal sequence. Amylase activity was found only in S. mutans cell extracts, with no activity detected in culture supernatants. Inactivation of amy by insertion of an antibiotic resistance marker confirmed that S. mutans has a single alpha-amylase activity. The amylase activity was induced by maltose but not by starch, and no acid was produced from starch. S. mutans can, however, transport limit dextrins and maltooligosaccharides generated by salivary amylase, but inactivation of amy did not affect growth on these substrates or acid production. The amylase digested the glycogen-like intracellular polysaccharide (IPS) purified from S. mutans, but the amy mutant was able to digest and produce acid from IPS; thus, amylase does not appear to be essential for IPS breakdown. However, when grown on excess maltose, the amy mutant produced nearly threefold the amount of IPS produced by the parent strain. The role of Amy has not been established, but Amy appears to be important in the accumulation of IPS in S. mutans grown on maltose.

SUBMITTER: Simpson CL

PROVIDER: S-EPMC107487 | biostudies-literature | 1998 Sep

REPOSITORIES: biostudies-literature

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Intracellular alpha-amylase of Streptococcus mutans.

Simpson C L CL Russell R R RR

Journal of bacteriology 19980901 17

Sequencing upstream of the Streptococcus mutans gene for a CcpA gene homolog, regM, revealed an open reading frame, named amy, with homology to genes encoding alpha-amylases. The deduced amino acid sequence showed a strong similarity (60% amino acid identity) to the intracellular alpha-amylase of Streptococcus bovis and, in common with this enzyme, lacked a signal sequence. Amylase activity was found only in S. mutans cell extracts, with no activity detected in culture supernatants. Inactivation ...[more]

PMID: 9721315

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Project description:Intracellular polysaccharides (IPS) are glycogen-like storage polymers which contribute significantly to Streptococcus mutans-induced cariogenesis. We previously identified and cloned a locus from the S. mutans chromosome which is required for the accumulation of IPS. Sequencing of this locus revealed at least four contiguous open reading frames, all of which are preceded by a common promoter region and are transcribed in the same direction. Analysis of the amino acid sequence deduced from the first of these open reading frames (ORF1) revealed domains which are highly conserved among D-alanine-activating enzymes (DltA) in Lactobacillus rhamnosus (formerly Lactobacillus casei) and Bacillus subtilis. The deduced amino acid sequences derived from ORF2, -3, and -4 also exhibit extensive similarity to DltB, -C, and -D, respectively, in these microorganisms. However, Southern hybridization experiments indicate that this operon maps to a locus on the S. mutans chromosome which is separate from the glgP, glgA, and glgD genes, whose products are known mediators of bacterial IPS accumulation. We therefore assigned a new dlt designation to the locus which we had formerly called glg. We maintain that the dlt genes are involved in S. mutans IPS accumulation, however, since they complement a mutation in trans which otherwise renders S. mutans IPS deficient. In this study, we found that expression of the S. mutans dlt genes is growth phase dependent and is modulated by carbohydrates internalized via the phosphoenolpyruvate phosphotransferase system (PTS). We demonstrated that the S. mutans dlt genes are expressed constitutively when non-PTS sugars are provided as the sole source of carbohydrate. Consistent with a role for the PTS in dlt expression is a similar constitutive expression of the dlt genes in an S. mutans PTS mutant grown in a chemically defined medium supplemented with glucose. In summary, these findings support a novel role for the dlt gene products in S. mutans IPS accumulation and suggest that dlt expression in this oral pathogen is subject to complex mechanisms of control imposed by growth phase, dietary carbohydrate, and other factors present in the plaque environment.

Dataset Information

Intracellular alpha-amylase of Streptococcus mutans.

Publications

Intracellular alpha-amylase of Streptococcus mutans.

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