Fermentation of pectin and glucose, and activity of pectin-degrading enzymes in the rabbit caecal bacterium Bifidobacterium pseudolongum.

Abstract

In a rabbit caecal bacterium Bifidobacterium pseudolongum, metabolites of pectin and glucose, and activities of enzymes involved in the degradation of pectin were assayed. Simultaneously, activities of these enzymes were assayed in a rumen pectinolytic strain of Streptococcus bovis. A strain B. pseudolongum P6 which grew best on pectin was selected among bifidobacteria isolated from the rabbit caecum. Cultures of B. pseudolongum P6 grown on pectin produced significantly less formate, lactate and ethanol, and more acetate and succinate than cultures grown on glucose. No CO2 production on pectin was observed. Pectin macromolecule was degraded by extracellular pectinase (EC 3.2.1.15). Cell extracts possessed the activity of 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase (EC 4.1.2.14). Streptococcus bovis X4, possessed activity of exopectate lyase and pectinase, but not that of KDPG aldolase. Our results are consistent with the assumption that in B. pseudolongum P6 acidic products of pectin degradation are catabolized via a modified Entner-Doudoroff pathway, as shown previously in rumen pectin-utilizing bacteria. The missing KDPG aldolase activity in Strep. bovis X4 seems to be the reason for the absence of growth of this bacterium on pectin. Information on polysaccharide metabolism in bifidobacteria is fragmentary. This study extends the knowledge on pectin metabolism in intestinal bacteria.