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This is Scientific American 60-Second Science. I'm Christopher Intagliata. Got a minute?

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

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They've ID'd the microbes in mosquito guts, coral mucus and frog skin; in polar ice; even floating in the Earth's atmosphere.

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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.

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So says a study in the journal BMC Biology.

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Researchers sequenced a pure sample of just one type of bacteria.

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But depending which kit they used, which reagents, which lab, their results contained DNA from up to 270 different bacterial strains.

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Many of those contaminating strains are commonly found on human skin¡ (a lab technician's, maybe?).

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Or in soil or water.

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Which could explain why one recent study turned up soil bacteria in samples of breast cancer tissue, the researchers say.

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Another study found that infants' throat bacteria change as they get older.

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But these researchers say the changing bacterial communities in that study were due not to age, but to changing the brand of DNA kit over time.

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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.

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"If you're doing fecal work, for example, this probably doesn't concern you,

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because there's enough DNA coming from the actual sample that it'll drown out any of the background contamination."

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His recommendation for scientists?

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Alongside the actual samples, try sequencing nothing¡ to see what sort of shadow microbiome is already lurking in your lab.

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Thanks for the minute, for Scientific American 60-Second Science. I'm Christopher Intagliata.

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