Just as we thought we had the human genome identified and sorted – even though each individual whole genome sequence (WGS) has about half a million unique characteristics there is a whole new arena to discover. The number of microbes that live on and in us now are thought to have profound effects on our internal metabolism. Estimates vary but J Craig Venter, someone worth listening to, estimates that there are 200 trillion microbes providing 10 million extra genes. Animals raised in germ free environments have significantly different metabolisms. Sandrine Claus in a new study notes that mice raised in this way who were then exposed to bedding of mice with normal microbiota (their digestive systems had the usual amount of probiotics or additional genetic contribution from microorganisms) showed rapid increases in weight and changes in liver metabolism. Food for thought.