STARCH UTILIZATION BY BACTEROIDES-OVATUS ISOLATED FROM THE HUMAN LARGE-INTESTINE

Starch supported growth of continuous cultures of Bacteroides ovatus w hen this carbohydrate provided the sole source of carbon and energy, I nducible amylase and alpha-glucosidase activities were inversely relat ed to dilution rate in starch-limited and starch-excess chemostats ove r the dilution rate (D) range D = 0.03/h to D = 0.20/h, and were partl y repressed during growth under conditions of starch-excess. Preparati ve isoelectric focusing of B. ovatus cytoplasmic extracts indicated th e existence of three distinct starch-hydrolyzing enzymes. Incubation o f active fractions from the isoelectric focusing cell with maltose and a variety of low-molecular weight oligosaccharides (maltotriose, malt otetraose, maltopentaose, maltohexaose, maltoheptaose) identified a si ngle amylase activity, an enzyme with combined beta-amylase and glucoa mylase/alpha-glucosidase properties, and also a possible pullulanase. The ability of B. ovatus to synthesize several starch-hydrolyzing enzy mes with different specificities and activities may confer a significa nt competitive advantage to this organism in the colonic ecosystem.