Screening and characterization of extracellular polysaccharides produced by Leuconostoc kimchii isolated from traditional fermented pulque beverage

We report the screening and characterization of EPS produced by LAB identified as Leuconostoc kimchii isolated from pulque, a traditional Mexican fermented, non-distilled alcoholic beverage produced by the fermentation of the sap extracted from several (Agave) maguey species. EPS-producing LAB constitutes an abundant bacterial group relative to total LAB present in sap and during fermentation, however, only two EPS-producing colony phenotypes (EPSA and EPSB, respectively) were detected and isolated concluding that despite the high number of polymer-producing LAB their phenotypic diversity is low. Scanning electron microcopy analysis during EPS-producing conditions revealed that both types of EPS form a uniform porous structure surrounding the bacterial cells. The structural characterization of the soluble and cell-associated EPS fractions of each polymer by enzymatic and acid hydrolysis, as by 1D- and 2D-NMR, showed that polymers produced by the soluble and cell-associated fractions of EPSA strain are dextrans consisting of a linear backbone of linked alpha-(1 -> 6) Glcp in the main chain with alpha-(1 -> 2) and alpha-(1 -> 3)-linked branches. The polymer produced by the soluble fraction of EPSB strain was identified as a class 1 dextran with a linear backbone containing consecutive alpha-(1 -> 6)-linked D-glucopyranosyl units with few alpha-(1 -> 3)-linked branches, whereas the cell-associated EPS is a polymer mixture consisting of a levan composed of linear chains of (2 -> 6)-linked beta-D-fructofuranosyl residues with beta-(2 -> 6) connections, and a class 1 dextran. According to our knowledge this is the first report of dextrans and a levan including their structural characterization produced by L. kimchii isolated from a traditional fermented source.