Impact of Laparoscopic Roux-en-Y gastric bypass and sleeve gastrectomy on gut microbiota: a metagenomic comparative analysis
Background Bariatric surgery is an effective therapeutic procedure for morbidly obese patients. The two most common interventions are Sleeve Gastrectomy (SG) and Laparoscopic Roux-en-Y Gastric Bypass (LRYGB).  Objectives The aim of this study was to compare microbiome long-term microbiome after SG and LRYGB surgery in obese patients.Methods89 and 108 patients who underwent SG and LRYGB respectively, were recruited. Stools were collected before and 6 months after surgery. Microbial DNA was analysed with shotgun metagenomic sequencing (SOLiD 5500xl Wildfire). MSPminer, a novel innovative tool to characterize new in silico biological entities, was used to identify 715 Metagenomic Species Pan-genome (MSPs). 148 functional modules were analysed using GOmixer and KEGG database.  Result Both interventions resulted in a similar increase of Shannon's diversity index and gene richness of gut microbiota, in parallel with weight loss, but the changes of microbial composition were different. LRYGB led to higher relative abundance of aero-tolerant bacteria, such as Escherichia coli and buccal species, such as Streptococcus and Veillonella spp. In contrast, anaerobes such as Clostridium were more abundant after SG, suggesting better conservation of anaerobic conditions in the gut. Enrichement of Akkermansia muciniphila was also observed after both surgeries. Function-level changes included higher potential for bacterial use of supplements such as vitamin B12, B1 and iron upon LRYGB.  Conclusion Microbiota changes after bariatric surgery depend on the nature of the intervention. LRYGB induces greater taxonomic and functional changes in gut microbiota than SG and may lead to a more dysbiotic microbiome. Possible long-term health consequences of these alterations remain to be established.