Degradation of Guar Gum by Enzymes Produced by a Bacterium From the Human Colon

A strain of Bacteroides ovatus from the human colon was grown on guar gum, a highly-branched galactomannan which is widely used as a food additive. Growth on guar gum induced production o f extracellular enzymes which partially degraded and/or deaggregated guar gum. The enzymes rapidly reduced the viscosity of guar gum solutions, while breaking only a limited number of glycosidic bonds. The molecular weight (versus dextran standards) of the guar gum decreased sharply as the viscosity decreased. No mono-, di- or trisaccharides were produced during enzyme action, although small quantities of higher oligomers were present after longer (5–8 h) incubations. The enzyme had a sharp temperature optimum at 37°C for an incubation time of 60 min, but was stable for only a few hours at this temperature. These results demonstrate how enzymes produced and elaborated by human colon bacteria can markedly alter the physical properties of a dietary component which reaches the colon. Further studies of both substrate and enzymes will be required to establish the mechanism of this alteration and to establish how B. ovatus is able to utilize guar gum for growth.