Mammals inherit most of their gut bacteria, new study suggests

It's never a good day to be a lab mouse.

Enlarge / It's never a good day to be a lab mouse. (credit: Getty | Portland Press Herald )

The communities of bacteria that live in most mammals’ guts are mostly passed down from mothers to their offspring, rather than traded among neighbors or picked up from the environment, suggests a new study in mice. But a few exceptions may suggest something interesting about the evolution of some human pathogens.

Inherited microbes

Bacteria living on and in your body outnumber your actual human cells several many times over. In your digestive tract, those invisible ecosystems play important roles not only in digestion but also in the immune system and the endocrine system, influencing the hormones that help regulate bodily functions. Those bacteria have to come from somewhere, whether they’re inherited in a process called vertical transmission in the womb or during childbirth or whether we pick them up from the environment or through contact with other people.

Fortunately for science, other animal species also carry whole ecosystems around in their digestive tracts, and mice reproduce much faster than humans (and are much more amenable to being kept in a carefully controlled laboratory environment for several generations). University of California Berkeley biologist Andrew Moeller and his colleagues spent three years breeding 17 separate lineages of mice in their laboratory (think of each lineage as a family tree with no branches). Some descended from mice caught in Arizona, while others traced their roots back to Alberta, Canada.

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