1887

Abstract

produces a number of extracellular sucrose-metabolizing enzymes that contribute to the ability of the organism to cause dental caries, including three glucosyltransferases, the products of the , and genes, and a fructosyltransferase, encoded by the gene. To better understand the regulation of the expression of these genes under environmental conditions that more closely mimic those in dental plaque, two strains of harbouring fusions of the (SMS102) and (SMS101) promoters to a chloramphenicol acetyltransferase (CAT) gene were examined in biofilms formed . The strains were grown in a Rototorque biofilm reactor in a tryptone-yeast extract-sucrose medium. CAT specific activity in biofilm cells was measured at quasi-steady state or following additions of 25 mM sucrose or glucose, with or without pH control. After approximately 10 generations of biofilm growth, the and genes of were found to be expressed at levels different from those reported for planktonic cells growing under otherwise similar conditions. The expression of these genes was induced by the addition of sucrose to the quasi-steady-state cultures. Expression of the genes was influenced by environmental pH, since CAT specific activities in quasi-steady-state biofilms of strain SMS102 grown without pH control were twice those produced by cells grown with pH control. Moreover, addition of glucose to quasi-steady-state biofilms resulted in increased expression of the fusion, although the magnitude of the induction was less than that seen with sucrose. The effect of pH on expression was negligible. A modest and transient induction of was observed in biofilms pulsed with excess glucose and the kinetics and level of induction of by excess carbohydrate were dependent on the pH of the biofilms. This study demonstrates that the type and amount of carbohydrate and the environmental pH have a major influence on transcription of the and genes when the organisms are growing in biofilms, and provides evidence for previously undisclosed regulatory circuits for exopolysaccharide gene expression in .

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2001-10-01
2020-09-28
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