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Biochemical and structural characterization of the glucan and fructan exopolysaccharides synthesized by the Lactobacillus reuteri wild-type strain and by mutant strains

Author: Geel-Schutten, G.H. van · Faber, E.J. · Smit, E. · Bonting, K. · Smith, M.R. · Brink, B. ten · Kamerling, J.P. · Vliegenthart, J.F.G. · Dijkhuizen, L.
Institution: Centraal Instituut voor Voedingsonderzoek TNO
Source:Applied and Environmental Microbiology, 7, 65, 3008-3014
Identifier: 235077
Keywords: Nutrition · Fructan · Glucan · Polysaccharide · Bacterial growth · Carbohydrate analysis · Carbohydrate synthesis · Food industry · Lactobacillus reuteri · Methylation · Nonhuman · Lactobacillus reuteri


Lactobacillus reuteri LB 121 cells growing on sucrose synthesize large amounts of a glucan (D-glucose) and a fructan (D-fructose) with molecular masses of 3,500 and 150 kDa, respectively. Methylation studies and 13C or 1H nuclear magnetic resonance analysis showed that the glucan has a unique structure consisting of terminal, 4-substituted, 6-substituted, and 4,6- disubstituted α-glucose in a molar ratio of 1.1:2.7:1.5:1.0. The fructan was identified as a (2 → 6)-β-D-fructofuranan or levan, the first example of levan synthesis by a Lactobacillus species. Strain LB 121 possesses glucansucrase and levansucrase enzymes that occur in a cell-associated and a cell-free state after growth on sucrose, raffinose, or maltose but remain cell associated during growth on glucose. Sodium dodecyl sulfate- polyacrylamide gel electrophoresis of sucrose culture supernatants, followed by staining of gels for polysaccharide synthesizing activity with sucrose as a substrate, revealed the presence of a single glucansucrase protein of 146 kDa. Growth of strain LB 121 in chemostat cultures resulted in rapid accumulation of spontaneous exopolysaccharide-negative mutants that had lost both glucansucrase and levansucrase (e.g., strain K-24). Mutants lacking all levansucrase activity specifically emerged following a pH shiftdown (e.g., strain 35-5). Strain 35-5 still possessed glucansucrase and synthesized wild- type glucan.