Fermentation of pectin and glucose, and activity of pectin-degrading enzymes in the rumen bacterium Lachnospira multiparus

Aims: Lachnospira multiparus belongs to the main rumen pectinolytic bacteria. Its carbohydrate metabolism was studied in growth experiments on laboratory fermenters, and using assays of activities of enzymes involved in pectin fermentation. Methods and Results: The type strain of this species and two substrates were used. Lachnospira multiparus ATCC 19207 grew on pectin and glucose at a similar rate and had no preference for one or the other substrate. Pectin-grown cultures, however, produced significantly more acetate and less formate, lactate, ethanol, hydrogen, cell dry matter and protein than corresponding cultures grown on glucose. Extracellular exopectate lyase (EC 4.2.2.9) was the principal enzyme degrading the pectin macromolecule. Cell extracts possessed 2-keto-3- deoxy-6-phosphogluconate aldolase (EC 4.1.2.14) and fructosediphosphate aldolase (EC 4.1.2.13) activity. The former enzyme catalyses the final reaction in the Entner-Doudoroff pathway; the latter is the key enzyme of glycolysis and the pentose phosphate pathway. Conclusions: These results are consistent with the assumption that acidic products of pectin degradation are catabolized via a modified Entner-Doudoroff pathway. Phosphogluconate was not metabolized by cell extracts of the strain studied. Significance and Impact of the Study: This suggests that the conventional Entner-Doudoroff pathway of glucose utilization does not operate in this bacterium, presumably because of the lack of 6-phosphogluconate dehydrase (EC 4.2.1.12) activity.