Extracellular polysaccharides of smooth and rough variants of Streptococcus salivarius

Some, but not all strains of Streptococcus salivarius were demonstrated to occur in smooth (S) and rough (R) variants, growing in distinctly different colonies on sucrose-containing agar plates. Sucrose-derived extracellular polysaccharides (EP) of NCTC 8606, ATCC 9759 S and R, ATCC 13419 S and R, 1A S and R, and Tove S and R were isolated, purified, and chemically studied. Extracellular enzymes of R variants yielded more water-insoluble than soluble material, while the opposite was true for S variants. The insoluble material consisted mainly of glucan, the soluble mainly of levan. Enzymatic hydrolysis suggested a predominance of alpha-1,3-linkages in the water-insoluble glucan. Cell-associated enzymes gave rise to cell-associated and -free EP. The cell-associated EP of S variants was insoluble, while that of R variants contained water-insoluble glucan and water-soluble fructan. Cells coated with cell-associated EP flocculated due to interaction of the EP, mainly by hydrogen bonding, in part by divalent cation bridging. The sucrose-derived EP gave rise to plaque deposit formation in sucrose broth cultures, S variant deposits being thin and firmly adherent to glass, R variant deposits being thick, rough, coherent, but only weakly adherent. The variant types were not altered by the curing agents ethidium bromide and acridine orange.