Characterization of alpha-L-rhamnosidase of Bacillus sp GL1 responsible for the complete depolymerization of gellan

A bacterium, Bacillus sp. GL1, depolymerizes a heteropolysaccharide (gellan ) to a tetrasaccharide (unsaturated glucuronyl-glucosyl-rhamnosyl-glucose) by extracellular gellan lyase. The resultant tetrasaccharide was degraded t o the constituent monosaccharides by subsequent reactions of unsaturated gl ucuronyl hydrolase, beta-D-glucosidase, and alpha-L-rhamnosidase. alpha-L-R hamnosidase was substantially induced in the bacterial cells when grown in a medium containing gellan as a carbon source. The purified enzyme from the cells was a monomer with a molecular mass of about 100 kDa and was most ac tive at pH 7.0 and 50 degrees C. The enzyme acted on the gellan-degrading p roduct (rhamnosyl-glucose) formed after successive reactions catalyzed by g ellan lyase, unsaturated-glucuronyl hydrolase and beta-D-glucosidase, and r eleased rhamnose from the disaccharide. Therefore, the alpha-L-rhamnosidase is found to be responsible as the final enzyme for the complete depolymeri zation of gellan. (C) 1999 Academic Press.