Evidence that polygalacturonic acid may not be a major source of carbon and energy for some colonic Bacteroides species

Five Bacteroides species that are found in the human colon can utilize polygalacturonic acid (PGA) when they are grown in laboratory media: Bacteroides thetaiotaomicron, Bacteroides vulgatus, Bacteroides ovatus, Bacteroides fragilis subsp. a, and Bacteroides sp. strain 3452A (an unnamed DNA-DNA homology group). PGA-degrading enzymes from B. thetaiotaomicron have been isolated and characterized previously. To determine whether a PGA lyase activity in human feces could be attributed to any of these species, we first determined the properties of PGA lyases from the other four Bacteroides species. PGA lyases from all the Bacteroides species were soluble, cell associated, and inducible by PGA. All had similar pH optima (8.4 to 8.8) and similar molecular weights (50,000). All activities were enhanced by calcium. The PGA lyases from the five species differed with respect to isoelectric point: B. thetaiotaomicron (pI 7.5), B. vulgatus (pI 7.7), B. ovatus (pI 5.8, 7.2), B. fragilis subsp. a (pI 6.1), and Bacteroides sp. strain 3452A (pI 7.7). The PGA lyase activity in human feces resembled those of the Bacteroides PGA lyases in that it had a pH optimum of 8.4 to 8.8 and was enhanced by calcium. However, it differed from the Bacteroides PGA lyases both with respect to isoelectric point (pI 4.2 to 4.4) and molecular weight (100,000). On the basis of these findings, it appears that the PGA lyase activity in human feces is not produced by any of the Bacteroides species surveyed in this survey. Moreover, there was no detectable PGA lyase activity in feces that had the same properties as the Bacteroides enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)