Clostridium ramosumPromotes High-Fat Diet-Induced Obesity in Gnotobiotic Mouse Models

ABSTRACTThe intestines of obese humans and mice are enriched with Erysipelotrichi, a class within the Firmicutes. Clostridium ramosum, a member of the Erysipelotrichi, is associated with symptoms of the metabolic syndrome in humans. To clarify the possible obesogenic potential of this bacterial species and to unravel the underlying mechanism, we investigated the role of C. ramosumin obesity development in gnotobiotic mice. Mice were associated with a simplified human intestinal (SIHUMI) microbiota of eight bacterial species, including C. ramosum, with the SIHUMI microbiota except C. ramosum(SIHUMIw/oCra), or with C. ramosumonly (Cra) and fed a high-fat diet (HFD) or a low-fat diet (LFD). Parameters related to the development of obesity and metabolic diseases were compared. After 4 weeks of HFD feeding, the mouse groups did not differ in energy intake, diet digestibility, gut permeability, and parameters of low-grade inflammation. However, SIHUMI and Cra mice fed the HFD gained significantly more body weight and body fat and displayed higher food efficiency than SIHUMIw/oCra mice fed the HFD. Gene expression of glucose transporter 2 (Glut2) in jejunal mucosa and of fatty acid translocase (CD36) in ileal mucosa was significantly increased in the obese SIHUMI and Cra mice compared with the less obese SIHUMIw/oCra mice. The data demonstrate that the presence of C. ramosumin SIHUMI and Cra mice enhanced diet-induced obesity. Upregulation of small intestinal glucose and fat transporters in these animals may contribute to their increased body fat deposition.IMPORTANCEObesity is a growing health problem worldwide. Changes in the proportions of Bacteroidetesand Firmicutes, the two dominant phyla in the human and the murine intestinal tract, link the intestinal microbiota to obesity. Erysipelotrichi, a class within the Firmicutes, increase in response to high-fat feeding in mice. Clostridium ramosum, a member of the Erysipelotrichi, has been linked to symptoms of the metabolic syndrome. We hypothesized that C. ramosumpromotes obesity development and related pathologies. Our experiments in gnotobiotic mice show that C. ramosumpromoted diet-induced obesity, probably by enhancing nutrient absorption. Identification of obesogenic bacteria and understanding their mode of action enable the development of novel strategies for the treatment of this epidemic disease. Pharmaceuticals that target obesogenic bacteria or their metabolism could help to prevent and treat obesity and related disorders in the future.