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Bacteria and archaea—collectively known as prokaryotes—live pretty much everywhere, dividing happily in places from stomach acid to deep-sea vents. They can thrive in so many different places because their genomes are incredibly flexible: they can alter, lose and duplicate genes almost at will. Scientists have long recognized that prokaryotes can also acquire genes from their neighbors (a move that contributes to antibiotic resistance). But this method of gaining new DNA, termed horizontal gene transfer, was thought to be relatively rare and to occur only under strong pressures in the environment, such as exposure to powerful antibiotics.

A recent study in PLoS Genetics has found, instead, that pro­kar­y­otes acquire genes from near-by microbes quite often. This transfer, which can take place when one bug obtains genetic information from another via a bridge or a virus, can happen even when the two prokaryotes are from different species.