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A team of marine biologists from the University of Washington discovered communities of microbes breathing arsenic in the oxygen deficient areas of the Pacific Ocean. The results suggest that microbial metabolism of arsenic may be underestimated in the modern ocean and would likely contribute significantly to biogeochemical cycles in ancient anoxic (oxygen – free) oceans arsenic were higher.
This colorized image shows a species of the genus haloarchaea Halorubrum. Scale bar – 2 mm. Image credit: Reid et al, doi: 10.1017 / S1473550406002916.
"In some parts of the ocean, there is a water sandwich where there is no measurable oxygen," said Professor Gabrielle Rocap, co – author of the. 39; study.
"The microbes in these regions must use other elements that act as electron acceptors to extract food energy."
The most common alternatives to oxygen are nitrogen or sulfur. However, the team's previous investigations had suggested that arsenic could also work, which prompted it to look for evidence.
The researchers analyzed samples taken during a science cruise in April 2012 in the tropical Pacific, off the coast of Mexico, aboard R / V Thompson.
They identified two known genetic pathways for converting arsenic – based molecules as a way to gain energy.
The genetic material targeted two different forms of arsenic and scientists believe that the transmission pathways occur in two organisms that perform an alternative cycle of arsenic between different forms.
The results suggest that arsenic-breathing microbes make up less than 1% of the microbial population in these waters.
The microbes found in the water are probably distantly related to the arsenic-breathing microbes found in hot springs or contaminated sites on land.
"What I think is the coolest thing about these arsenic – breathing microbes existing today in the ocean, is that they express the genes that make it. constitute in a fairly poor arsenic environment, "said Dr. Jaclyn Saunders, first author of the study. .
"This paves the way for places where we could search for arsenic – breathing organisms in other arsenic – poor environments.
Biologists believe that this strategy is a vestige of the beginnings of the Earth. During the period when life was born on Earth, oxygen was scarce in the air and in the ocean. Oxygen in the Earth's atmosphere was only abundant when photosynthesis became widespread and turned carbon dioxide into oxygen.
The first life forms had to gain energy by using other elements, such as arsenic, which was probably more common in the oceans at that time.
"We have found genetic signatures of pathways that are still there, remnants of the old ocean maintained until today," said Dr. Saunders.
The results were published this week in the Proceedings of the National Academy of Sciences.
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Jaclyn K. Saunders et al. Complete arsenic-based respiratory cycle in marine microbial communities of pelagic oxygen-deficient areas. PNAS, published online April 29, 2019; doi: 10.1073 / pnas.1818349116
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