Not all research has confirmed or identified all of the bacterial strains teeming in our guts but 5 new books break down what you need to know to transform your body's second brain. We carry up to 2 kg of microbes in our gut, and there are at least 1,000 species of bacteria consisting of over 3 million genes. Two thirds of the gut microbiome, which is the population of microbes in the intestine is unique to each individual.