Human gut microbiota 16S rRNA in lean, obese, and post-gastric-bypass individuals

Recent evidence suggests that the microbial community in the human intestine may play an important role in the pathogenesis of obesity. We examined 184,094 sequences of microbial 16S rRNA genes from PCR amplicons using the 454 pyrosequencing technology to compare the microbial community structures of nine individuals - three in each of the categories of normal-weight, morbidly obese, and following gastric-bypass surgery. Phylogenetic analysis showed that, although the Bacteria in the human intestinal community were highly diverse, they fell mainly into six bacterial divisions that had distinct differences among normal-weight, obese, and gastric-bypass individuals. Specifically, Firmicutes were dominant in normal-weight and obese individuals, but significantly decreased in gastric-bypass subjects, who had a proportional increase of Gammaproteobacteria. Members of the H2-producing Prevotellaceae were highly enriched in the obese individuals. Unlike the highly diverse Bacteria, Archaea were mainly composed of members of the order Methanobacteriales, which are H2-oxidizing methanogens. Using real-time PCR, we detected significantly higher numbers of H2-utilizing methanogenic Archaea in obese individuals than in normal-weight or individuals following gastric-bypass. The co-existence of H2-producing bacteria with relatively high numbers of H2-utilizing methanogenic Archaea in the gastrointestinal tract of obese individuals leads to the hypothesis that interspecies H2 transfer between bacterial and archaeal species is an important mechanism for increasing energy uptake by the human large intestine in obese individuals. The large bacterial population shift in gastric bypass individuals may reflect the double impact of the gut alteration caused by the surgical procedure and the consequent change in food ingestion and digestion.