Role of intracellular polysaccharide in persistence of Streptococcus mutans

Intracellular polysaccharide (IPS) is accumulated by Streptococcus 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 t