Microbiome

Gut–brain axis

Bacteroidetes

Firmicutes

16S ribosomal RNA

Obesity

Bacteria

Gut flora

Biology

Gene

Endocrinology

Metagenomics

Immunology

Genetics

Nature

The worldwide obesity epidemic is stimulating efforts to identify host and environmental factors that affect energy balance. Comparisons of the distal gut microbiota of genetically obese mice and their lean littermates, as well as those of obese and lean human volunteers have revealed that obesity is associated with changes in the relative abundance of the two dominant bacterial divisions, the Bacteroidetes and the Firmicutes. Here we demonstrate through metagenomic and biochemical analyses that these changes affect the metabolic potential of the mouse gut microbiota. Our results indicate that the obese microbiome has an increased capacity to harvest energy from the diet. Furthermore, this trait is transmissible: colonization of germ-free mice with an ‘obese microbiota’ results in a significantly greater increase in total body fat than colonization with a ‘lean microbiota’. These results identify the gut microbiota as an additional contributing factor to the pathophysiology of obesity. Our gut microbes do us a service by performing metabolic chores that we have not evolved to do for ourselves. In a sense their genes are part of the 'metagenome' that is Homo sapiens. That is illustrated by two related papers in this issue that present evidence for a microbial component to obesity. A study of the abundance of the two dominant groups of bacteria in the gut of obese individuals shows that increased numbers of Bacteroidetes bacteria correlate with weight loss. And a study of genetically obese mice reveals that their gut microbial community has a greater capacity for harvesting energy than that of lean littermates: the trait is transmissible by transplanting the community into germ-free mice. This work suggests that the gut microbiome associated with obesity might be a biomarker and possibly a therapeutic target.

An obesity-associated gut microbiome with increased capacity for energy harvest