A young researcher in NASA's astrobiology program set off an international controversy last year when she reported that strange microbes in the muddy brine of Mono Lake were thriving and reproducing on arsenic - a toxic element deadly to every other life form known on Earth.
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2011/05/27/BA011JMGBK.DTL