Role of Intracellular Polysaccharide in Persistence of Streptococcus mutans

Abstract

Intracellular polysaccharide (IPS) is accumulated byStreptococcus mutans when the bacteria are grown in excess sugar and can contribute toward the cariogenicity of S. mutans. Here we show that inactivation of the glgA gene (SMU1536), encoding a putative glycogen synthase, prevented accumulation of IPS. IPS is important for the persistence of S. mutans grown in batch culture with excess glucose and then starved of glucose. The IPS was largely used up within 1 day of glucose starvation, and yet survival of the parental strain was extended by at least 15 days beyond that of a glgA mutant; potentially, some feature of IPS metabolism distinct from providing nutrients is important for persistence. IPS was not needed for persistence when sucrose was the carbon source or when mucin was present.Streptococcus mutans is a facultative colonizer of the human dental plaque, the microbial pellicle that covers the surface of the teeth. It is the major etiological agent of dental caries (17). Sugar metabolism is central to the behavior of S. mutans (4, 7). It can use a variety of sugars. The sugars are fermented by glycolysis with production of organic acids, particularly lactic acid (4, 7). In addition to providing energy, sucrose is used to produce extracellular polysaccharides to form the biofilm matrix that aids in the association of S. mutans with the dental plaque. Once the S. mutans biofilm becomes part of the dental plaque, the acidic by-products of sugar fermentation dissolve tooth enamel, eventually resulting in dental caries (17). The presence of sugars in the dental plaque is periodic and reflects the intake of dietary sugars. If there is excess sugar available, in addition to producing organic acids and matrix, intracellular (iodophilic) polysaccharide (IPS; glycogen) is formed.The IPS of S. mutans is a polymer of the glycogen-amylopectin type, with ␣-(1, 4)-and ␣-(1, 6)-linked glucose, and is stored as intracellular granules (10). Intracellular glycogen storage reserves in various bacterial species are synthesized from glucose-1-P via ADP-glucose (1). The synthesis involves at least three enzymes: glycogen synthase, glucose-1-phosphate pyrophosphorylase, and branching enzyme. The genes encoding these enzymes are commonly found in a glg operon, although the order of genes differs between species. In two gram-positive species, Bacillus subtilis and Bacillus stearothermophilus, the gene order is glgB-glgC-glgD-glgA-glgP (15, 29): glgA encodes glycogen synthase, glgB encodes glucan branching enzyme, and glgC and glgD encode subunits of glucose-1-phosphate pyrophosphorylase. The glgP gene encodes glycogen phosphorylase, which is unlikely to be involved in glycogen synthesis (29). Genes putatively encoding similar enzymes are present in the same order in the genome of S. mutans (29); they are thought also to form an operon.The IPS can be used as a source of carbohydrate for fermentation upon nutrient depletion (11, 13). In planktonic cultures, IPS reserves are largely consumed within 12 h of the imposition of sugar starv...

Antimicrobial peptide GH12 suppresses cariogenic virulence factors of Streptococcus mutans

“…Lack of EPS disrupts both adherence of bacteria and the structure of biofilm. When exogenous substrate is depleted, S. mutans can metabolize IPS [50]. Therefore, malfunction of GTFs not only directly disrupt the biofilm integrity, but also may enhance the starvation stress of S. mutans due to reduced preservation of IPS.…”

Transcriptome analysis reveals that ClpXP proteolysis controls key virulence properties of Streptococcus mutans

“…The synthesis of IPS has been implicated in enhanced survival of S. mutans and has been shown to contribute to caries formation (Gibbons & Socransky, 1962;Spatafora et al, 1995;van Houte et al, 1970). Previous work revealed that production of IPS via glgA (encoding glycogen synthase) significantly extended the survival of S. mutans during starvation, especially when cells were grown in the presence of glucose (Busuioc et al, 2009). The upregulation of several glg genes led us to hypothesize that the enhanced long-term survival of DclpP and DclpX (Kajfasz et al, 2009) could be associated with increased IPS storage.…”

“…Accumulation of stored IPS was evaluated by using a colorimetric assay that relies on the formation of an iodinepolysaccharide complex (Busuioc et al, 2009). Briefly, bacteria were streaked on Todd-Hewitt agar plates containing 2 % glucose or 2 % sucrose and incubated for 48 h. The plates were then flooded with 5 ml iodine solution [0.2 % (w/v) iodine in 2.0 % (w/v) potassium iodide solution].…”

The Tea Catechin Epigallocatechin Gallate Suppresses Cariogenic Virulence Factors of Streptococcus mutans

“…The malfunction of GTFs at the lower pH value may lead to reduced production of EPS and IPS. The latter can be metabolized when exogenous fermentable substrate is depleted in the oral cavity (10). Therefore, the malfunction of GTFs may disrupt both bacterial adherence to the tooth surface and biofilm integrity and may augment the starvation stress of S. mutans cells due to the reduced preservation of IPS.…”