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...
Despite many modern wastewater treatment solutions, the most common is still the use of activated sludge (AS). Studies indicate that the microbial composition of AS is most often influenced by the raw sewage composition (especially influent ammonia), biological oxygen demand, the level of dissolved oxygen, technological solutions, as well as the temperature of wastewater related to seasonality. The available literature mainly refers to the relationship between AS parameters or the technology used and the composition of microorganisms in AS. However, there is a lack of data on the groups of microorganisms leaching into water bodies whose presence is a signal for possible changes in treatment technology. Moreover, sludge flocs in the outflow contain less extracellular substance (EPS) which interferes microbial identification. The novelty of this article concerns the identification and quantification of microorganisms in the AS and in the outflow by fluorescence in situ hybridization (FISH) method from two full-scale wastewater treatment plants (WWTPs) in terms of 4 key groups of microorganisms involved in the wastewater treatment process in the context of their potential technological usefulness. The results of the study showed that Nitrospirae, Chloroflexi and Ca. Accumulibacter phosphatis in treated wastewater reflect the trend in abundance of these bacteria in activated sludge. Increased abundance of betaproteobacterial ammonia-oxidizing bacteria and Nitrospirae in the outflow were observed in winter. Principal component analysis (PCA) showed that loadings obtained from abundance of bacteria in the outflow made larger contributions to the variance in the PC1 factorial axis, than loadings obtained from abundance of bacteria from activated sludge. PCA confirmed the reasonableness of conducting studies not only in the activated sludge, but also in the outflow to find correlations between technological problems and qualitative and quantitative changes in the outflow microorganisms.
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