Selection of bacteria originating from a human intestinal microbiota in the gut of previously germ-free rats

Denaturing gradient gel electrophoresis (DGGE) was applied to separate PCR-amplified 16S rRNA genes originating from human microbiota associated (HMA) rat faeces as well as from the human faecal sample used for inoculation of the animals. Subsequently, a total of 15 dominant bands were excised from the DGGE gels, cloned and sequenced. Comparison of the obtained sequences with the Ribosomal Database revealed that species of Bacteroides/Prevotella and Faecalibacterium gave rise to the majority of the dominant bands in the human sample and in the HMA rats. In the HMA rats, two dominant bands, which were not present in the human DGGE profile, originated from species of Ruminococcus. With the exception of the Ruminococcus sequences, sequences originating from both rats and human samples were represented in all major branches of a maximum parsimony tree, indicating that the rat feed and gut environment allows colonization of the dominant taxonomic units from the human microbiota, but additionally selects for Ruminococci. Bands representing Prevotella and Faecalibacterium, which were found in identical positions of the DGGE gels originating from human and HMA rat faecal samples, originated from completely identical sequences, indicating that the same strains of these species were dominating in the human and rat samples.