Lactobacillus reuteri Strains Convert Starch and Maltodextrins into Homoexopolysaccharides Using an Extracellular and Cell-Associated 4,6-α-Glucanotransferase

Exopolysaccharides (EPS) of lactic acid bacteria (LAB) are of interest for food applications. LAB are well-known to produce alpha-glucan from sucrose by extracellular glucansucrases. Various Lactobacillus reuteri strains also possess 4,6-alpha-glucanotransferase (4,6-alpha-GTase) enzymes. Purified 4,6-alpha-GTases (e.g, GtfB) were shown to act on starches (hydrolysates), cleaving alpha l -> 4 linkages and synthesizing alpha l -> 6 linkages, yielding isomalto-/maltopolysaccharides (IMMP). Here we report that also L. reuteri cells with these extracellular, cell -associated 4,6-alpha-GTases synthesize EPS (alpha-glucan) from starches (hydrolysates). NMR, SEC, and enzymatic hydrolysis of EPS synthesized by L. reuteri 121 cells showed that these have similar linkage specificities but generally are much bigger in size than IMMP produced by the GtfB enzyme. Various LMMP-like EPS are efficiently used as growth substrates by probiotic Bifidobacterium strains that possess amylopullulanase activity. IMMP-like EPS thus have potential prebiotic activity and may contribute to the application of probiotic L. reuteri strains grown on maltodextrins or starches as synbiotics.