Sucrose-promoted accumulation of growing glucosyltransferase variants of Streptococcus gordonii on hydroxyapatite surfaces

Streptococcus gordonii exhibits a phase variation involving expression of high (Spp⁺) or low (Spp^-) glucosyltransferase activity. The related bacterial accumulation on hydroxyapatite (HA) and saliva-coated HA surfaces was examined and found to be significant. Spp⁺ cells growing anaerobically in a defined medium utilize about 30% of the glucose available from sucrose to make insoluble glucans. These glucans formed cohesive masses on HA beads, which contained 80 to 90% of the total bacteria. The bacterial polymer mass had a volume of about 40 μm³ and contained more than 5 x 10¹⁰ viable cells per cm³. In the absence of sucrose, the beads were saturated by 1 x 10⁸ to 2 x 10⁸ Spp⁺ cells. Spp^- bacteria, which make 30-fold less glucan than do Spp⁺ bacteria, did not accumulate on surfaces in numbers significantly above the saturation level of 1 x 10⁸ to 2 x 10⁸ cells in the presence or absence of sucrose. Insoluble glucan synthesized by Spp⁺ cells from sucrose also enabled these bacteria to accumulate on saliva-coated HA seven times more effectively than the Spp^- cells and 10 times more effectively than the Spp⁺ cells grown in medium without sucrose.