title: A Bacteroides ovatus chromosomal locus which contains an alpha-galactosidase gene may be important for colonization of the gastrointestinal tract.
abstract: An alpha-galactosidase gene has been cloned from the human colonic Bacteroides species Bacteroides ovatus 0038. This alpha-galactosidase appears to be distinct from two previously characterized alpha-galactosidases, I and II, from the same strain and has been designated alpha-galactosidase III. Partially purified alpha-galactosidase III from Escherichia coli EM24 containing pFG61 delta SE had a pI of 7.6, as compared with the reported pI values for the known alpha-galactosidases of 5.6 for I and 6.9 for II. Its molecular weight as estimated on sodium dodecyl sulfate-polyacrylamide gels was 78,000, whereas the molecular weights of alpha-galactosidases I and II were 85,000 and 80,500, respectively. The only substrate hydrolyzed by alpha-galactosidase III was melibiose, whereas the other two alpha-galactosidases were able to degrade melibiose, raffinose, and stachyose and partially degraded guar gum. alpha-Galactosidase III had a pH optimum of 6.7 to 7.2. Finally, a single crossover insertion which disrupted the gene in the B. ovatus chromosome had no effect on expression of alpha-galactosidases I and II. Although this insertion had no effect on the ability of B. ovatus to grow in laboratory medium on any of the galactoside-containing carbohydrates tested, the insertion mutant was outcompeted by wild type when a combination of mutant and wild type was used to colonize germfree mice. Insertions on either side of the gene had the same effect. Thus, the locus which contains alpha-galactosidase III may be important for colonization in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Microbiology, University of Illinois, Urbana 61801.
authors.forename: P J
authors.initials: PJ
authors.lastname: Valentine
authors.forename: F C
authors.initials: FC
authors.lastname: Gherardini
authors.forename: A A
authors.initials: AA
authors.lastname: Salyers
mesh_terms: D000818:Animals; D001439:Bacteroides / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004064:Digestive System / Q000382:microbiology*; D004926:Escherichia coli / Q000235:genetics; D005260:Female; D015870:Gene Expression; D005798:Genes, Bacterial; D005856:Germ-Free Life; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D015183:Restriction Mapping; D013379:Substrate Specificity; D000519:alpha-Galactosidase / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D000519:alpha-Galactosidase