Imagine a planet with an atmosphere lacking oxygen, its landscape dotted with volcanic craters, caustic oceans, and basins of brine. Yet, amazingly, these oceans and brines teem with life, albeit very different from our own-microorganisms that breathe arsenic. That description may describe the Earth during the early Archean eon.
Although breathing arsenic may sound alien, microorganisms that use arsenic oxyanions for anaerobic respiration are found in environmental niches ranging from garden soil and subsurface aquifers to more extreme landscapes such as Mono Lake and Searles Lake in California. Diverse microorganisms metabolize both inorganic and organic forms of arsenic, and their activities are part of a robust biogeochemical cycle. What began more than 15 years ago as our quest to learn how bacteria use arsenate as a terminal electron acceptor led us to discover novel respiratory and photosynthetic pathways.