A new study published in Scientific Reports has discovered that arsenic and selenium may have been more prevalent in the early evolution of life on earth than previously thought. The work may also lead to innovations for treating contaminated environments.

Duquesne University researchers analyzed more than 1,500 protein sequences of enzymes with molybdenum at their core to determine which were most ancient. They found that enzymes that were involved in methane, arsenic and selenium metabolism were indeed ancient. What made this work unique was the large number of protein sequences and the method of analysis.

"Our approach was to look at proteins to recreate a record so that we can get an idea of how these enzymes evolved in the world," said Dr. John Stolz, environmental microbiology professor and director of Duquesne's Center for Environmental Research and Education. "Using that information, we have been able to confirm it with geochemical evidence."

The research may help inform environmental experts who work with arsenic issues, especially in places such as Bangladesh, where arsenic-contaminated drinking water lead to increases in cancer and other diseases.

There has been a long-standing debate among scientists about how to determine which dimethyl sulfoxide reductase (DMSOR) enzymes were most prevalent at life's origins.

"Our work is the first comprehensive analysis of the DMSOR family that identifies when specific lineages diversified from the family through geologic time," Stolz said. "Previous methods have been inadequate in determining such lineages. This study found that both arsenic and selenium played important roles in the global biogeochemical cycle, and that arsenic likely sustained microbial communities."

Future studies of DMSOR enzymes may illuminate how organisms and biogeochemical cycles have co-evolved as the Earth's oxidation state has increased over time, he added.

"For example, by better understanding arsenic metabolism, which first occurred more than 2.5 billion years ago, researchers may gain clues to understanding how to protect humans from such contaminates," Stolz said.

In addition to Stolz, co-authors of the paper include Michael Wells, Narthana Jeganathar Kanmanii, Al Muatasim Al Zadjali and Dr. Jan Janecka of Duquesne's Department of Biological Sciences in the School of Science and Engineering; Dr. Partha Basu of Indiana University-Purdue University Indianapolis; and Ronald Oremland of the U.S. Geological Survey.

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August 27, 2020