Structural diversity of streptococcal mutans synthesized under different culture and environmental conditions and its effect on mutanase synthesis

Abstract

Streptococcal mutans synthesized under different conditions by growing cultures or by their glucosyltransferases were shown to exhibit a great structural and property diversity. Culturing and environmental factors causing structural differences in mutans were specified. All of the obtained biopolymers (76 samples) were water-insoluble and most of them (72) had a structure with a predominance of α-(1→3)-linked glucose (i.e., the content of α-(1→3)-linkages in the glucan was always higher than 50%, but did not exceed 76%). An exception were four glucans containing more than 50% of α-(1→6)-sequences. In these structurally unique mutans, the ratio of α-(1→3)- to α-(1→6)-bonds ranged from 0.75 to 0.97. Aside from one polymer, all others had a heavily branched structures and differed in the number of α-(1→3), α-(1→6), and α-(1→3,6) linkages and their mutual proportion. The induction of mutanase production in shaken flask cultures of Trichoderma harzianum by the structurally diverse mutans resulted in enzyme activities ranging from 0.144 to 1.051 U/mL. No statistical correlation was found between the total percentage content of α-(1→3)-linkages in the α-glucan and mutanase activity. Thus, despite biosynthetic differences causing structural variation in the mutans, it did not matter which mutan structures were used to induce mutanase production.

Figure 1

¹H-NMR spectra of selected streptococcal mutans. Anomeric signals of: (A) α-(1→3)-linked glucose; (B) α-(1→3)-linked glucose substituted at O-6; (C) α-(1→6)-linked glucose substituted at O-3; (D) α-(1→6)-linked glucose. Samples were dissolved in 30% NaOD in D₂O and spectra were recorded at 300 MHz at 60 °C.

Figure 2

Relationship between mutanase activity obtained on particular mutans as enzyme inducers (76 samples) and the total content of α-(1→3)-linkages in each of these polymers (for details see Table 4). The data obtained from statistical analysis: Pearson correlation (R), determination (R²), and linear regression (y), p < 0.05.