Human intestinal microbiota Characterization of a simplified and stable gnotobiotic rat model

The study of host microbe interactions is hampered by the complexity and inter-individual variability of the human gut microbiota. Therefore, a simplified human intestinal microbiota (SIHUMI) consisting of seven bacterial species was introduced into germfree rats. Species selection was based on numerical importance and fermentative abilities in the human gut. Association of the rats with the SIHUMI (Anaerostipes caccae, Bacteroides thetaiotaomicron, Bifidobacterium longum, Blautia producta, Clostridium ramosum, Escherichia coli and Lactobacillus plantarum) resulted in increased fecal concentrations of short chain fatty acids compared to germfree animals. Since the fecal butyrate concentration was low (0.9 +/- 0.5 mu mol/g dry matter) the SIHUMI was complemented with Clostridium butyricum. This extended bacterial community (SIHUMIx) led to an increased fecal butyrate concentration of 1.5 +/- 0.7 mu mol/g dry matter. Besides forming SCFA, the SIHUMIx was capable of degrading mucins, beta-aspartylglycine and bilirubin. These features are characteristic of conventional animals but not observed in germfree animals. Dietary interventions with modifications in fibre and fat content led to changes in the proportion of community members. The relative increase of one member of this community in response to a high-fat diet reflects the situation reported for obese mice and human subjects. The strength of the model communities is their remarkable stability over time and their easy transfer to the offspring.