Research from the University of Georgia has found that inorganic mercury, previously thought to be a less harmful form of the toxic metal, is very damaging to key cell processes. The study compared the effects of inorganic and organic mercury compounds at the biochemical, physiological, and proteomic levels in a model organism.
“Today, most human exposure to inorganic mercury is from dental fillings, and organic mercury exposure is from methylmercury in fish,” said Anne Summers, a microbiology professor at the university’s Franklin College of Arts and Sciences and a co-author of the study.
Organic mercury exposure is linked with neurological disease, while inorganic mercury causes neurological, kidney, and autoimmune diseases, though the molecular basis for their distinct toxicity profiles has not been understood. Most research has emphasized organic mercury due to concerns about fish consumption. Yet inorganic mercury causes more damage at lower concentrations, the study said.
The researchers used a common lab strain of Escherichia coli bacteria as a model cellular system. Next, they exposed growing cells to mercury compounds and used a fluorescent probe to measure their reactive sulfur thiols, which are essential metals and proteins that naturally bind essential metals via amino acid thiols.
The thiols decreased more after inorganic mercury exposure than organic mercury exposure. Also, the inorganic mercury was much more efficient at removing iron from iron-depended proteins than the best organic mercury compound tested.
“As fellow oxygen-breathing creatures, it’s important to know that inorganic mercury is more potent than organic mercury in disrupting protein-iron centers such as those we have in our own cells,” said Summers.
“More is being learned about the bacteria in and on our bodies,” said Stephen LaVoie, a microbiology doctoral student and lead author of the study. “What we ingest affects them, too, and their health affects our health.”
Future work will examine the mercury resistance genes that many bacteria have and how these genes help spread antibiotic resistance genes. The study, “Organic and Inorganic Mercurials Have Distinct Effects on Cellular Thiols, Metal Homeostasis, and Fe-binding Proteins in Escherichia Coli,” was published by the JBIC Journal of Biological Inorganic Chemistry.