All forms of life that breathe oxygen -- even ones that can't be seen with the naked eye, such as bacteria -- must fight oxidants to live. But neutralizing environmental oxidants such as superoxide was a worry only for organisms that dwell in sunlight -- in habitats that cover a mere 5 percent of the planet. That was the only place where such environmental oxidants were thought to exist. Now researchers have discovered the first light-independent source of superoxide. The key is bacteria common in the depths of the oceans and other dark places.
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