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

Leuconostoc mesenteroides strain NRRL B-1355 produces two soluble extracell ular alpha-D-glucans from sucrose: alternan and dextran, An unusual mutant strain derived from NRRL B-1355 has recently been isolated which produces p ractically no soluble polysaccharide, but significant amounts of an insolub le 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 insolu ble residue. Treatment of the soluble dextranase-limit fraction with an alp ha(1-->2) debranching enzyme led to further dextranase susceptibility. Meth ylation, FTIR and NMR analyses of the dextranase-treated fractions indicate a non-uniform structure with domains bearing similarities to L. mesenteroi des strain NRRL B-1299 dextran and to insoluble streptococcal D-glucans.