Degradation of pectins with different degrees of esterification by Bacteroides thetaiotaomicron isolated from human gut flora

A complete human fecal flora and cultures of defined species obtained from fecal flora were investigated in vitro to determine their ability to fermen t the dietary fiber pectin. Bacteroides thetaiotaomicron was tested as a pe ctin-degrading microorganism alone and in coculture with Escherichia coli. Macromolecular pectins with different degrees of esterification were used a s substrates in microbial degradation studies. The levels of oligogalacturo nic acids formed in batch cultures were estimated during a 24- or 48-h incu bation period by using highperformance thin-layer chromatography and high-p erformance anion-exchange chromatography. The spectrum and the amount of un saturated oligogalacturonic acids formed as intermediate products of pectin fermentation changed permanently in the culture media during incubation wi th the complete fecal flora. After 24 h, no oligogalacturonic acids were de tected. The pectin-degrading activities of pure cultures of B. thetaiotaomi cron were lower than the pectin-degrading activity of a complete fecal flor a. Cocultures of B. thetaiotaomicron and E. coli exhibited intermediate lev els of degradation activity. In pure cultures of E. coli no pectin-degradin g activity was found. Additionally, the rate of pectin degradation was affe cted by the degree of esterification of the substrate. Saturated oligogalac turonic acids were not found during pectin fermentation. The disappearance of oligogalacturonic acids in the later stages of fermentation with both th e complete fecal flora and B. thetaiotaomicron was accompanied by increased formation of short-chain fatty acids.