Life is fragile, but it also has the ability to overcome adversity in ways we might not expect. One such example is the discovery of microorganisms in the tropical Pacific Ocean that are capable of employing arsenic in their metabolism.

As reported in Proceedings of the National Academy of Sciences, the researchers were looking for evidence of peculiar metabolisms in regions of the ocean where there is no oxygen when they discovered that there is a small percentage (less than one) that use arsenic for cellular respiration instead of nitrogen and sulfur like the vast majority. A handful of species have been found to use arsenic in their metabolism but scientists have never discovered organisms that do so in the ocean.

The researchers believe the ability is leftover from the ancient Earth. As oxygen was scarce at the time, the first life-forms did not use it. Instead, arsenic may have been one of the ways they extracted energy, which was more abundant at the time in the ocean.

“What I think is the coolest thing about these arsenic-respiring microbes existing today in the ocean is that they are expressing the genes for it in an environment that is fairly low in arsenic,” first author Dr Jaclyn Saunders, from Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology, said in a statement. “It opens up the boundaries for where we could look for organisms that are respiring arsenic, in other arsenic-poor environments.”

The starting point of this investigation was a specific difference in certain types of arsenic ions seen in the ocean compared to what theory said. Researchers suspected that the discrepancy might have been due to some living organism, so they went and looked for evidence.

“We’ve known for a long time that there are very low levels of arsenic in the ocean,” explained co-author Gabrielle Rocap, a professor of oceanography at the University of Washington. “But the idea that organisms could be using arsenic to make a living – it’s a whole new metabolism for the open ocean. For me, it just shows how much is still out there in the ocean that we don’t know.”

The team collected bits and pieces of the organisms' genomic information, enough to show that they have the ability to deal with arsenic. They found the organisms employ two genetic pathways, each dealing with either arsenate or arsenite molecules. While these organisms are thriving in these oxygen-free environments, many species don't. The team is worried that no-oxygen regions are only destined to grow because of global warming. 

Next up for the team is to extract the full genome of the organisms in order to better understand how they have adapted to their environment.