Arsenic Loving Bacteria May Help in Search For Alien Life

 

The first organism able to substitute one of the six chemical elements crucial to life has been found. The bacterium, found in a California lake, uses the usually poisonous element arsenic in place of phosphorus.
The find, described in Science, gives weight to the long-standing idea that life on other planets may have a radically different chemical makeup. It also has implications for the way life arose on Earth - and how many times it may have done so.

The "extremophile" bacteria were found in a briny lake in eastern California. While bacteria have been found in inhospitable environments and can consume what other life finds poisonous, this bacterial strain has actually taken arsenic on board in its cellular machinery. Until now, the idea has been that life on Earth must be composed of at least the six elements carbon, hydrogen, oxygen, nitrogen, sulphur and phosphorus. No example had ever been found that violates this golden rule of biochemistry.

The bacteria were found as part of a hunt for life forms radically different from those we know.  "At the moment we have no idea if life is just a freak, bizarre accident which is confined to Earth or whether it is a natural part of a fundamentally biofriendly universe in which life pops up wherever there are Earth-like conditions," explained Paul Davies, the Arizona State University and Nasa Astrobiology Institute researcher who co-authored the research. "Although it is fashionable to support the latter view, we have zero evidence in favour of it. If that is the case then life should've started many times on Earth - so perhaps there's a 'shadow biosphere' all around us and we've overlooked it because it doesn't look terribly remarkable. Proof of that idea could come in the form of organisms on Earth that break the "golden rules" of biochemistry - in effect, finding life that evolved separately from our own lineage.  The take-home message is: who knows what else is there? We've only scratched the surface of the microbial realm”

Study lead author Felisa Wolfe-Simon and her colleagues Professor Davies and Ariel Anbar of Arizona State University initially suggested in a paper an alternative scheme to life as we know it.  Their idea was that there might be life in which the normally poisonous element arsenic (in particular as chemical groups known as arsenates) could work in place of phosphorus and phosphates. Putting it to the test, the three authors teamed up with a number of collaborators and began to study the bacteria that live in Mono Lake in California, home to arsenic-rich waters.

The researchers began to grow the bacteria in a laboratory on a diet of increasing levels of arsenic, finding to their surprise that the microbes eventually fully took up the element, even incorporating it into the phosphate groups that cling to the bacteria's DNA. Notably, the research found that the bacteria thrived best in a phosphorus environment.  That probably means that the bacteria, while a striking first for science, are not a sign of a "second genesis" of life on Earth, adapted specifically to work best with arsenic in place of phosphorus. However, Professor Davies said, the fact that an organism that breaks such a perceived cardinal rule of life makes it is a promising step forward.
"This is just a weird branch on the known tree of life," said Professor Davies. "We're interested ultimately in finding a different tree of life... that will be the thing that will have massive implications in the search for life in the Universe.

The general consensus is that this really could still be an evolutionary adapatation rather than a second genesis. But it's the early days of this project and it's certainly a theory to think about and keep looking for, that second genesis. What it certainly shows is the astonishing and perhaps under-appreciated versatility of life and prompts questions as to the possible elements on remote Earth-like planets. And what are the  implications regarding extraterrestrial life?