Everglades wetlands area

More microorganisms than first thought may contribute to process of increasing mercury toxicity

New research published in the journal Applied and Environmental Microbiology indicates the types of microorganisms that could transform mercury into methylmercury is higher than previously thought. The study took samples from four sites in the Florida Everglades. Drs. Hee-Sung Bae and Andrew Ogram with the UF/IFAS Soil and Water Sciences Department (SWS) and Forrest Dierberg with DB Environmental of Rockledge, Fla., conducted the research.

“This work is, for the first time, exploring the structure of microbial populations converting mercury to the neurotoxin methylmercury in the Everglades,” said Bae, a biological scientist.

Periphyton in the Florida Everglades is defined by the U.S. E.P.A. as a complex assemblage of algae, cyanobacteria, microinvertebrates, their secretions, and detritus attached to submerged surfaces. This study found the greatest concentrations of methylmercury were found in flocculent material (the layer just above the peat soil) and periphyton. (Photo provided)

Mercury is present in most environments, but when it is transformed via methylation, the element becomes more toxic. In water, fish consume it and methylmercury accumulates in their bodies. That causes it to become toxic to anything that eats the fish.

Experts have believed sulfate-reducing bacteria (SRB) have been the main group of microorganisms responsible for the methylation. The new research finds those bacteria may not be as important to the production of methylmercury.

“What we have shown here is the interaction between sulfate and methylmercury production is not as straight-forward as originally thought,” said Ogram, professor of Microbial Ecology and Molecular Biology. “The farther you get away from the sulfate source, the less important these sulfate-reducing bacteria probably are. Even in areas with higher sulfate concentrations, it’s a much more complex system than originally thought.”

A gene that encodes the enzyme system that controls mercury methylation was identified through research at Oak Ridge National Laboratory several years ago. That finding has opened the door to more research into the process and what bacteria may have the capabilities to do it. Bae and his colleagues started screening samples from a variety of places that accumulate methylmercury, and not all had high levels of sulfate.

“It turns out a lot of bacteria, actually, have the capability of methylating mercury,” Ogram pointed out. “Some use sulfate, some use iron, some use carbon dioxide, a lot of different metabolisms are capable of doing this.”

While the results shed new light on the process of methylation, more questions remain.

“All we can say is which bacteria are capable of producing the methylmercury and that they’re complex and it’s really a difficult picture here and interesting, but we don’t know if they’re really doing it,” said Ogram. “So, the next step is to use more sophisticated methods to see who is truly active in this process.”

You can read the full journal article HERE.