Arsenic is a deadly poison for most living things, but new research has found microorganisms in a low-oxygen area of the Pacific Ocean that breathe arsenic.
University of Washington professor of oceanography Gabrielle Rocap is a co-author of the study, published April 29, 2019, in the peer-reviewed journal Proceedings of the National Academy of Sciences. Rocap said in a statement:
We’ve known for a long time that there are very low levels of arsenic in the ocean. But the idea that organisms could be using arsenic to make a living – it’s a whole new metabolism for the open ocean.
The team analyzed samples collected during a 2012 research cruise to the tropical Pacific, off the coast of Mexico. The seawater samples came from a region below the surface, where oxygen is almost absent. Rocap said:
In some parts of the ocean there’s a sandwich of water where there’s no measurable oxygen. The microbes in these regions have to use other elements that act as an electron acceptor to extract energy from food.
Genetic analyses on DNA extracted from the seawater found two genetic pathways that are known to convert arsenic-based molecules as a way to gain energy.
According to the researchers, the microbes discovered in the water are probably distantly related to the arsenic-breathing microbes found in hot springs or contaminated sites on land.
Biologists believe the strategy of using arsenic for respiration is a holdover from Earth’s early history. During the period when life arose on Earth, oxygen was scarce in both the air and in the ocean. Oxygen became abundant in Earth’s atmosphere only after photosynthesis became widespread and converted carbon dioxide gas into oxygen. Early lifeforms had to gain energy using other elements, such as arsenic, which was likely more common in the oceans at that time.
We found the genetic signatures of pathways that are still there, remnants of the past ocean that have been maintained until today.
Arsenic-breathing populations may grow again under climate change. Low-oxygen regions are projected to expand, and dissolved oxygen is predicted to drop throughout the marine environment. Rocap said:
For me, it just shows how much is still out there in the ocean that we don’t know.
Bottom line: Researchers have discovered microorganisms that breathe arsenic.
Eleanor Imster has helped write and edit EarthSky since 1995. She was an integral part of the award-winning EarthSky radio series almost since it began until it ended in 2013. Today, as Lead Editor at EarthSky.org, she helps present the science and nature stories and photos you enjoy. She also serves as one of the voices of EarthSky on social media platforms including Facebook, Twitter and G+. She and her husband live in Tennessee and have two grown sons.