Methylobacterium sp. isolated from a Finnish paper machine produces highly pyruvated galactan exopolysaccharide

The slime-forming bacterium Methylobacterium sp. was isolated from a Finnish paper machine and its exopolysaccharide (EPS) was produced on laboratory scale. Sugar compositional analysis revealed a 100% galactan (EPS). However, FT-IR showed a very strong peak at 1611 cm−1 showing the presence of pyruvate. Analysis of the pyruvate content revealed that, based on the sugar composition, the EPS consists of a trisaccharide repeating unit consisting of d-galactopyranose and [4,6-O-(1-carboxyethylidene)]-d-galactopyranose with a molar ratio of 1:2, respectively. Both linkage analysis and 2D homo- and heteronuclear 1H and 13C NMR spectroscopy revealed the following repeating unit: →3)-[4,6-O-(1-carboxyethylidene)]-α-d-Galp-(1→3)[4,6-O-(1-carboxyethylidene)]-α-d-Galp-(1→3)-α-d-Galp-(1→. By enrichment cultures from various ground and compost heap samples a polysaccharide-degrading culture was obtained that produced an endo acting enzyme able to degrade the EPS described. The enzyme hydrolysed the EPS to a large extent, releasing oligomers that mainly consisted out of two repeating units.