In order to find the bacteria capable of converting the mercury, we turned to the contaminated materials themselves. Bacteria are ubiquitous in the environment and can be found on any surface. Ideally adapted to the particular environment they are inhabiting, the bacteria on the surface of a mercury-treated item will have inherent resistance to the mercury toxicity. Our job was to find these naturally mercury-resistant bacteria and determine if they are converting the mercury into a gas. In collaboration with the Arizona State Museum, upon sampling nine mercury-contaminated museum materials, including leather pouches and feathered headdresses, 16 mercury-resistant bacteria were identified. Of the 16 bacterial isolates, one in particular was highly resistant capable of growing in the presence of up to 50 ppm mercury. This isolate, genetically identified as Arthrobacter sp. 2604, a commonly found environmental bacterium, had the ability to convert the mercury in its immediate environment into a gaseous form. When Arthrobacter sp. 2604 was grown on the surface of mercury-contaminated materials, including paper, the bacterium was able to remove up to 20% of the mercury within a 10 day incubation period. The other isolates, also identified as commonly occurring bacteria such as Bacillus and Pseudomonas spp., showed varying abilities to grow in the presence of mercury. Future experiments will focus on enhancing the mercury removal by the bacteria on other material types, e.g., hair and leather. The novel approach of using microorganisms for mercury removal has widespread applications for contaminated environments and is an exciting new application for microorganisms in museums.
This research was made possible through Grant MT-2210-04-NC-08 from the National Center for Preservation Technology and Training (NCPTT).