Gut microbiota (formerly called gut flora) is the microbe population living in our intestine
Our gut microbiota contains tens of trillions of microorganisms, including at least 1000 different species of known bacteria with more than 3 million genes (150 times more than human genes). Microbiota can, in total, weigh up to 2 kg. One third of our gut microbiota is common to most people, while two thirds are specific to each one of us.
In other words, the microbiota in your intestine is like an individual identity card.
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