Structural characterization of the surface-associated heteropolysaccharide of Lactobacillus plantarum TMW 1.1478 and genetic analysis of its putative biosynthesis cluster.

Microbial exopolysaccharides (EPS) like xanthan are widely exploited as natural biopolymers in diverse industrial sectors. In foods, in-situ EPS formation by starter cultures allows the manufacturing of "clean labeled" products with improved textural and nutritional properties. We performed structural analyses of the cell surface-associated EPS produced by Lactobacillus plantarum TMW 1.1478, which is a promising starter culture for fermented foods. Chromatographic analyses and NMR experiments suggested an acetylated heptameric repeating unit comprised of glucose, rhamnose and galactose as major components, whereas analysis of the macromolecular HePS structure suggested an apparent molecular mass of Mr ∼2 × 106 and a root mean square (RMS) radius of ca. 60 nm. Genetic analyses enabled the identification of the respective EPS biosynthesis cluster, and its modular organization supports the chemically identified, novel EPS structure. The obtained results broaden the understanding of complex EPS formation from activated sugar nucleotides by Lactobacillus plantarum.