Dysbiosis, including decreased gut microbial richness (MGR) and composition modifications, associates with adverse metabolism in lean, overweight or moderate obesity, but lacks characterization in severe obesity. Bariatric surgery (BS) improves body composition and metabolism in severe obesity which featuresand is associated with gut microbiota modifications. Here, we characterized the importance of dysbiosis and functional alterations in severe obesity and assessed whether BS procedures would rescue this dysbiosis.. Major microbiota dysbiosis in severe obesity: fate after bariatric surgery

Dysbiosis, including decreased gut microbial richness (MGR) and composition modifications, associates with adverse metabolism in lean, overweight or moderate obesity, but lacks characterization in severe obesity. Bariatric surgery (BS) improves body composition and metabolism in severe obesity which featuresand is associated with gut microbiota modifications. Here, we characterized the importance of dysbiosis and functional alterations in severe obesity and assessed whether BS procedures would rescue this dysbiosis. Methods61 Sixty-one severely obese subjects, candidate to adjustable gastric banding (AGB, n=20) or Roux-en-Y-gastric bypass (RYGB n=41), were enrolled. 24 of them were followed at 1, 3 and 12 months post-BS. Gut microbiota and serum metabolomeics were analyzed using shotgun metagenomics and LC-MS technology, respectively. ResultsLow gene richness (LGC) concerned was present in 75% of patients and associated with detrimental fat composition (increased trunk-fat mass) and cardiometabolic complications (type-2 diabetes, hypertension and its severity). 78 Seventy-eight metagenomic species (MGS) were signatures of LGC , among which 50 % associated with adverse body composition and metabolic phenotypes. Nine serum metabolites (including Glutarate, 3-Methoxyphenylacetic Acid, and L-Histidine) and functional modules containing protein families involved in their metabolism were strongly modified byassociated with MGR. Gut microbiome showed significant increase of MGR one-year post-BS. Yet, RYGB patients remained with major dysbiosis one year post-BS, despite better improvement of their metabolism compared to AGB. Conclusions: We found signatures of major dysbiosis in severe obesity which include decreased MGR and related-functional alterations linked with metabolic deteriorations. The lack of full rescue post-BS, plead call for added strategies to improve the gut microbiota ecosystem and microbiome-host interactions in severe obesity.