Anaerobic Photosynthesis

Researchers have found two microbial species that use arsenite (AsO₃^3-) to supply electrons for photosynthesis instead of water typically used by most plants (Science 2008, 321, 967).

During photosynthesis, plants use sunlight to extract electrons from water and donate them to carbon dioxide. They then use the carbon and hydrogen to build biomass and release oxygen as a by-product.

But a team led by Ronald S. Oremland of the U.S. Geological Survey discovered red- and green-colored microbes growing in anoxic, hot-spring-fed brine pools at Mono Lake, in California, that extract electrons from arsenite instead of water. The researchers identified the microbes? quirky metabolism while growing the organisms in the lab. Only after exposing each microbe to light did they find that arsenite was being oxidized to arsenate (AsO₄^3-).

These species of microbes and other so-called extremophiles are thought to have evolved almost 3 billion years ago as a consequence of their seemingly inhospitable, low-oxygen environment. The newly discovered chemistry provides a further glimpse of what life might have been like on early Earth, the researchers note.