Some structural features of an insoluble α-D-glucan from a mutant strain of Leuconostoc mesenteroides NRRL B-1355

Leuconostoc mesenteroides

strain NRRL B-1355 produces two soluble extracellular α-D-glucans from sucrose: alternan and dextran. An unusual mutant strain derived from NRRL B-1355 has recently been isolated which produces practically no soluble polysaccharide, but significant amounts of an insoluble D-glucan. Methylation analysis shows it contains linear (1→3) and (1→6) linkages as well as (1→2) and (1→3) branch linkages. The insoluble glucan was partially digestible by endodextranase, giving rise to a series of oligosaccharides, a high-molecular weight soluble fraction and an insoluble residue. Treatment of the soluble dextranase-limit fraction with an α(1→2) debranching enzyme led to further dextranase susceptibility. Methylation, FTIR and NMR analyses of the dextranase-treated fractions indicate a non-uniform structure with domains bearing similarities to L. mesenteroides strain NRRL B-1299 dextran and to insoluble streptococcal D-glucans.