New Tool for Studying Toxic Metals in the Environment

Method enables quantification of thiols on bacteria and natural organic matter.

Image courtesy of Oak Ridge National Laboratory
Baohua Gu and colleagues at Oak Ridge National Laboratory have developed a method to determine the total number of sulfur compounds called thiols on intact bacterial cells and natural organic matter. This technique will enable scientists to better examine the interactions between thiols and metal contaminants such as mercury in the environment.

The Science

Organic thiols are a class of reduced sulfur compounds that occur in soil, fresh, and marine water environments. Thiols are known to react and form complexes with several toxic soft metals such as mercury in both living and nonliving systems. However, a clear understanding of these interactions is limited because quantifying thiols in environmental matrices is difficult due to their low abundance, susceptibility to oxidation, and measurement interference by non-thiol compounds in samples. To better understand the processes that regulate the fate and transport of metal ions such as mercury, a robust and sensitive analytical approach for quantifying organic thiols on bacteria and natural organic matter (NOM) is needed.

The Impact

A team of scientists from Oak Ridge National Laboratory (ORNL) has developed a fluorescence-labeling method to determine, for the first time, total thiols on both intact gram-negative bacterial cells and environmental NOM samples. The new technique will enable future studies on the complex interactions and uptake mechanisms of contaminant metals by bacteria in the environment.


The method uses a fluorescence-labeling reagent consisting of a thiol-reactive maleimide group known as ThioGlo-1 (TG-1). TG-1 has been used for determining thiols in biological proteins and tissues but never for directly quantifying thiols on bacteria and NOM. The ORNL team systematically evaluated and optimized the labeling conditions to minimize potential interferences with non-thiol compounds. They applied the optimized conditions to Geobacter sulfurreducens PCA (a gram-negative methylating bacterium) and its mutants in culture solutions, as well as to two NOM samples. Their method proved to be highly selective and capable of quantifying thiols at sub-micromolar concentration levels. This ability to directly quantify organic thiols on NOM and bacterial cells will help scientists gain a mechanistic understanding of soft metal and microbial interactions, metal speciation, and bioavailability.


Baohua Gu
Oak Ridge National Laboratory


This research was sponsored by the Office of Biological and Environmental Research within the U.S. Department of Energy’s Office of Science as part of the Mercury Science Focus Area program at Oak Ridge National Laboratory.


Rao, B., et al. “Determination of thiol functional groups on bacteria and natural organic matter in environmental systems.” Talanta 119, 240–247 (2014). [DOI: 10.1016/j.talanta.2013.11.004].

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