Regulated Expression of the Streptococcus mutans dlt Genes Correlates with Intracellular Polysaccharide Accumulation

Abstract

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) inLactobacillus rhamnosus (formerlyLactobacillus 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. mutanschromosome which is separate from the glgP,glgA, and glgD genes, whose products are known mediators of bacterial IPS accumulation. We therefore assigned a newdlt designation to the locus which we had formerly calledglg. We maintain that the dlt genes are involved in S. mutans IPS accumulation, however, since they complement a mutation in trans which otherwise rendersS. 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 dltexpression is a similar constitutive expression of the dltgenes 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 inS. mutans IPS accumulation and suggest thatdlt 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.

Association of CiaRH with resistance of Streptococcus mutans to antimicrobial peptides in biofilms

“…This tran-scriptional start site in strain UA159 was different from that reported previously in strain UA130 (4 bp upstream of the site in UA159). Additionally, the DNA sequence of this region in the UA159 strain was slightly different from that reported previously (Spatafora et al, 1999). Based on the result of our RACE experiment, we predicted the promoter region of dltA, although the -10 region in the dltA promoter has two matches to the canonical -10 sequence.…”

The ADP‐glucose pyrophosphorylase from Streptococcus mutans provides evidence for the regulation of polysaccharide biosynthesis in Firmicutes

“…Results obtained for S. mutans ADP-Glc PPase also could be analysed concerning the intracellular metabolic scenario (Fig. 9), since there is an important background regarding sugar utilization and IPS synthesis in oral streptococci (Gibbons and Kapsimalis, 1963;Gibbons, 1964;van Houte et al, 1969;van Houte and Saxton, 1971;Freedman and Coykendall, 1975;Huis in 't Veld and Backer Dirks, 1978;Birkhed and Tanzer, 1979;Takahashi et al, 1991;Spatafora et al, 1999;Takahashi and Nyvad, Fig. 8.…”

Glycogen contributes to the environmental persistence and transmission of Vibrio cholerae

“…The role glycogen metabolism plays in bacterial pathogenesis is not clear. A number of reports suggest a role by demonstrating that glycogen aids colonization (Jones et al, 2008) acid production (Harris et al, 1992;Spatafora et al, 1999) and persistence at mucosal surfaces (Carlson et al, 2008). A role for glycogen metabolism in Salmonellae virulence is unclear.…”