Metabolism of the Polysaccharides of Human Dental Plaque: Release of Dextranase in Batch Cultures of Streptococcus mutans

Abstract

~~~~ ~Dextranase activity was determined in cell extracts and cell-free filtrates of Streptococcus mutans strains which had been grown in batch culture. Exo-dextranase activity was located chiefly in cell extracts, whereas endodextranase was mainly extracellular. Release of endo-dextranase began early in the exponential phase of growth, and ended when the concentration of residual sugar was low. Thus, dextranase expression was associated with rapidly growing cells, and the yield of dextranase was increased several fold when the initial concentration of D-glucose in the medium was changed from 0.5% to 2%. The endo-dextranase was not stable at pH 5 , and control of the pH of the culture was essential to preserve active dextranase during overnight growth. Strain Ingbritt (serotype c) and serotype d strains were the best dextranase producers; other strains (serotypes a, b, c, e and f) displayed much lower activity. The ability to produce endo-dextranase, and to synthesize a-D-glucans with a high proportion of (1 -3)-linked sequences, appeared to be related properties. The possibility is discussed that the release of two enzymes, namely endodextranase and the D-glucosyltransferase (GTF-I) that synthesizes ( 1 +3)-a-D-glUCan, are factors that contribute to the cariogenicity of S . mutans serotype d.

Multilevel control of extracellular sucrose metabolism in Streptococcus salivarius by sucrose

“…Furthermore, in this catabolic capacity, dextranase would be acting as an antagonist to the extracellular GTFs, thus explaining the apparent low levels of GTF activity in this organism. In fact, the presence of dextranase may obscure any conclusions made in studies of GTF in any organism producing both these enzyme activities and consequently, any reaction influenced by dextran (aggregation, adherence and the distribution of GTFs between cell-surfaces and culture supernatants) (Walker et al, 1981). Work is continuing on determining the molecular basis of sucrose activation of dextranase, and the effect of dextranase on the apparent production of GTF.…”

“…Under all conditions tested, cell-associated activity for these enzymes was not detected, indicating that both dextranase and fructanase are extracellular enzymes. If an intracellular dextranase exists in this organism, as in related streptococci (Dewar & Walker, 1975;Walker et al, 1980;Walker et al, 1981 ;, its activity was not measurable under these conditions. Dextranase levels were similar whether the cells were grown in glucose, fructose or galactose; the same held true for fructanase (levanase) levels (Fig.…”

Glucan-binding Proteins of the Oral Streptococci

“…The significance of the dextranase inhibitor, Dei, may be to affect the ratio of GTF to dextranase (Sun et al, 1994), which, in turn, influences the synthesis of water-insoluble glucan (Walker et al, 1981;Tanzer et al, 1985). Shaw et al (1997) have determined that, at low growth rates, the activity of free Dei is high, and predominantly water-soluble glucan is synthesized.…”

Sugar metabolism by mutans streptococci

“…mutans. The sequences of all these proteins can be aligned on the basis of their b sheets and a 1977; Walker et al 1981). This activity may modify glucans by altering the ratio of a(1-6)-to a(1-3)-linked chains, hence…”