Diet-Induced Obesity in Gnotobiotic Mouse Models Promotes High-Fat Clostridium ramosum 2014

The 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. ramosum in 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. ramosum only (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. ramosum in 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. IMPORTANCE Obesity is a growing health problem worldwide. Changes in the proportions of Bacteroidetes and 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. ramosum promotes obesity development and related pathologies. Our experiments in gnotobiotic mice show that C. ramosum promoted 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. Received 26 June 2014 Accepted 2 September 2014 Published 30 September 2014 Citation Woting A, Pfeiffer N, Loh G, Klaus S, Blaut M. 2014. Clostridium ramosum promotes high-fat diet-induced obesity in gnotobiotic mouse models. mBio 5(5):e01530-14. doi:10.1128/mBio.01530-14. Invited Editor Jose Clemente, University of Colorado Editor Maria Gloria Dominguez Bello, New York University School of Medicine Copyright © 2014 Woting et al. This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-ShareAlike 3.0 Unported license, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original author and source are credited. Address correspondence to Michael Blaut, blaut@dife.de. The rising prevalence of obesity and its comorbidities, including type 2 diabetes, hypertension, and cardiovascular disease, requires further efforts to better understand the pathogenesis of these conditions. In humans and mice, obesity is accompanied by a reduction of intestinal Bacteroidetes and a concomitant increase of Firmicutes (1, 2). However, this finding was not confirmed in other human studies, which did not show an increased Firmicutes/ Bacteroidetes ratio in obese subjects (3, 4). The high proportion of Firmicutes observed in obese mice was in part due to the proliferation of Erysipelotrichi, a bacterial class within this phylum (5). An increased abundance of intestinal Erysipelotrichi was also observed in mice fed a Western diet (6, 7) and in an obese human individual (8). This bloom of Erysipelotrichi suggests a role of these bacteria in obesity development. A recent study in type 2 diabetic women linked the presence of Clostridium ramosum, a member of the Erysipelotrichi, to symptoms of the metabolic syndrome (9). In support of this finding, obesity in human subjects was associated with low bacterial gene content and increased abundance of C. ramosum (10). These studies suggest that C. ramosum may be critically involved in obesity development. However, the underlying mechanisms are obscure. Several mechanisms have been proposed to explain obesogenic effects of intestinal bacteria. Bacterial glycoside hydrolases cleave nondigestible polysaccharides (dietary fiber) to oligoand monosaccharides, which subsequently undergo bacterial fermentation mainly to short-chain fatty acids (SCFA). The latter provide additional energy to the host (7, 11, 12). Glucose released during bacterial depolymerization of polysaccharides may promote hepatic lipogenesis (13) and could thereby contribute to obesity development. High-fat diets (HFD) increase intestinal permeability and thereby facilitate the absorption of bacterial lipopolysaccharides (LPS) (14, 15). Increased serum LPS levels were identified as one RESEARCH ARTICLE crossmark September/October 2014 Volume 5 Issue 5 e01530-14 ® mbio.asm. org 1 m b.asm . rg on O cber 3, 2014 P ubished by m b.asm . rg D ow nladed fom