A New Kind of Life

Bacteria that use arsenic in their DNA could reshape our idea of the chemistry of life.

It was almost A dogma among biologists that the basic chemical constituents of life were restricted to the six elements—carbon, hydrogen, nitrogen, oxygen, sulphur and phosphorous—that make up the basic material of life such as proteins, lipids and nucleic acids. The possibility of alternate chemistries for life has often been suggested, and it is a theme that has been played out even in science fiction, most notably by Arthur C Clarke. The serious scientific alternatives that have been examined are silicon instead of carbon, chlorine instead of oxygen and arsenic instead of phosphorous. The speculations in each depend on the close parallels between the chemistry of the respective elements.

Felisa Wolfe-Simon (her Twitter moniker is Iron Lisa) of Nasa's Astrobiology Institute had been interested in the case for arsenic because it  "is biologically so similar to phosphate that many enzymes cannot recognize the difference. …In fact, in contrast to phosphorus, arsenic readily forms sulfides and thus may have been available to early life at hydrothermal vents and similar environments. Given the distinct similarity between these two elements my co-authors and I assemble plausible testable hypotheses regarding the likelihood of life arising to either originally incorporate arsenate in a functional sense, and/or more speculatively, alternative forms of life utilizing a genetic system entirely based on arsenic.''

Wolfe-Simon and her colleagues found bacteria in a lake in California that seemed to manage to live amidst high arsenic concentration. In the laboratory, they found the bacteria could grow in solutions with high phosphorous or arsenic concentrations. When they studied the bacteria grown in high arsenic concentration, they found arsenic had been utilised in their DNA as well as protein.

The paper further reveals that the bacteria seem to prosper better with phosphorous suggesting early life near hydrothermal vents could have initially used arsenic and then switched to phosphorous. Even if this were not the case, the findings are revolutionary, expanding the possible elements of life.