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Analytical Chemistry

Understanding Cadmium Toxicity In Bacteria

The metal diminishes cellular stores of manganese and zinc, and makes bacteria sensitive to oxidative stress

by Michael Torrice
March 16, 2015 | A version of this story appeared in Volume 93, Issue 11

Electronic waste is a big source of cadmium pollution.
Credit: Shutterstock
Electronic waste releases significant amounts of cadmium into the environment.

Cadmium enters the environment mainly through industrial sources, including burning fossil fuels and recycling electronic waste. Despite cadmium’s accumulation, scientists don’t fully understand the molecular mechanisms behind its toxicity in cells, especially how it leads to oxidative stress. Now researchers in Australia explain that, in a model bacterial organism, the metal causes problems by depleting the cell’s internal stores of manganese and zinc (Nat. Commun. 2015, DOI: 10.1038/ncomms7418). Christopher A. McDevitt of the University of Adelaide and colleagues found that Cd2+ sneaks into Streptococcus pneumoniae by competing with Mn2+ for a certain transporter protein complex. When Cd2+ gets inside, the cell’s metal-sensing machinery mistakes it for Zn2+ and triggers the expression of proteins that export Zn2+. The team also determined that Cd2+ doesn’t directly cause oxidative stress. Instead, the resulting low Mn2+ levels lead to decreased expression of an enzyme that removes superoxide radicals. Without this enzyme, the cells become sensitive to reactive oxygen species. Replenishing Mn2+ in the cells, even when Cd2+ concentrations are high, restores the enzyme’s expression and the cell’s ability to withstand oxidative stress.


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