This is Scientific American 60 Second Science.

I'm Christopher in D'Alga.

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In this age of cheap DNA technology, scientists are sequencing every sample they can get their hands on.

They've IDed the microbes in mosquito guts, coral mucus, and frog skin,

in polar ice, even floating in the Earth's atmosphere.

But it turns out some of the bugs reported to belong to

those unusual microbiomes could unfortunately be contaminants from non-sterile

lab reagents and DNA extraction kits. So says a study in the journal

BMC biology. Researchers sequenced a pure sample of just one type of

bacteria, but depending which kit they used, which reagents, which lab,

their results contain DNA from up to 270 different bacterial strains.

Many of those contaminating strains are commonly found on human skin.

A lab technicians, maybe, or in soil or water,

which could explain why one recent study turned up soil bacteria

in samples of breast cancer tissue, the researchers say.

Another study found that infant's throat bacteria change as they get older,

but these researchers say the changing

the brand of DNA kit over time.

Study author Alan Walker of the University of Aberdeen

says contamination is only a problem if you're working with

samples that aren't already rich in bacteria. If you're doing fecal work for

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