Importance of mucopolysaccharides as substrates for Bacteroides thetaiotaomicron growing in intestinal tracts of exgermfree mice

Abstract

We used two approaches to determine whether the mucopolysaccharide chondroitin sulfate is an important source of carbon and energy for Bacteroides thetaiotaomicron in the intestinal tracts of germfree mice. First, we tested the ability of three mutants that grew poorly or not at all on chondroitin sulfate to colonize the intestinal tract of a germfree mouse and to compete with wild-type B. thetaiotaomicron in this model system. One mutant (CG10) was rapidly outcompeted by the wild type. However, since this mutant was unable to grow on chondroitin sulfate because it could not grow on N-acetyl-galactosamine, one of its monosaccharide components, this mutant might also be unable to utilize glycoprotein mucins. Two mutants (46-1 and 46-4) were isolated that grew poorly on chondroitin sulfate but normally on both component sugars. One of them was outcompeted by the wild type, but the percent wild type increased more slowly than with CG10. In one experiment, the percent wild type never reached 100%. The other (46-4) was not outcompeted by the wild type. These results indicate that, although chondroitin sulfate may be a carbon source in the animal, it is not of major importance. Our second approach was to determine by immunoblot analysis whether a 28-kilodalton outer membrane protein that is produced by B. thetaiotaomicron only when it is grown on chondroitin sulfate or hyaluronic acid was being produced at induced level by B. thetaiotaomicron growing in the ceca of exgermfree mice. There was no evidence for induction of this protein in vivo. Thus, the immunoblot results are consistent with results of the mutant competition experiments.