An enzyme system hydrolysing the polysaccharides of Xanthomonas species

Abstract

AbstractEnzymes hydrolysing the exopolysaccharides of Xanthomonas campestris and related species (xanthan) have been obtained from a Bacillus species isolated by enrichment culture. Growth on xanthan induced a number of enzymes acting on the xanthan molecule. These included one or more β‐glucanohydrolases and β‐glucosidases, together with mannosidases. The former activities were also present in cultures grown in the presence of laminaran or scleroglucan, but not in simple synthetic media with glucose as substrate. Partial purification of the enzymes active on glucans was achieved by ammonium sulphate precipitation and chromatography on DEAE‐sepharose and CM‐sepharose. The specificity of the β‐glucosidase and the β‐glucanohydrolase were investigated. Several β‐glucans were hydrolysed to glucose and disaccharides, but there was no activity against β→ 6 linked polymers, cellulose azure or microcrystalline cellulose. Carboxymethylcellulose was hydrolysed, as were laminaran, scleroglucan and pachyman. Activity was greater against the β→ 4 linked glucans than against the β→ 3 linked glucans tested. As periodate‐oxidized laminarin was also hydrolysed, it was concluded that the glucanohydrolase acted as an endoenzyme. The β‐glucosidase had a pH optimum at about 8–2 and a temperature optimum at 45°C; it showed higher activity against o‐nitrophenyl‐D‐glucopyranoside, cellobiose, trehalose and sophorose than against gentibiose.