Motility as a Factor in Bowel Colonization by Roseburia cecicola, an Obligately Anaerobic Bacterium from the Mouse Caecum

Roseburia cecicola strain GM is a motile obligate anaerobe that was isolated from mouse caecal mucosa. Twenty-five strains of motility mutants were obtained from populations of strain GM (wild-type) that had been exposed to UV light. Unlike GM cells, mutant bacteria were either non-motile and non-flagellated (Fla-) or migrated slowly or atypically in semi-solid medium. Strain GM and two mutant strains, SLS (Fla-) and WES (atypically motile), were used in mouse colonization experiments. In separate experiments, each strain colonized (4.8 X 10(9) to 1.5 X 10(10) c.f.u. per g caecum) the caecum of germfree mice inoculated intragastrically with pure cultures of the bacteria. In mice mono-associated with either mutant strain, bacteria which were non-motile or atypically motile predominated in their caeca (greater than 99% of total bacteria recovered). In mice mono-associated with motile cells of strain GM, mutant strains which had lost wild-type motility became predominant in the caecal populations (97% of total bacteria recovered at 48 to 70 days after inoculation). Mice mono-associated with either strain SLS or strain GM were colonized by one strain each of Escherichia coli, Candida pintolopesii, a Bacteroides sp., and a Clostridium sp. Most (99%) of the R. cecicola cells recovered from the caeca of these animals had typical wild-type motility. Motility, although not essential for R. cecicola to colonize germfree mice, is apparently advantageous to this bacterium when other micro-organisms are present with it in the mouse caecum. Motility may thus be essential for R. cecicola to colonize conventional laboratory mice.