PRJNA539962
Swift Evolutionary Response of Microbes to Historical Rise in Anthropogenic Mercury Deposition throughout the Northern Hemisphere
Anthropogenic remobilization of toxic heavy metals such as mercury (Hg) has considerably increased since the onset of the Industrial Revolution in the late 1700s, reaching environments far from their emission points. While total Hg levels can be determined from environmental archives, there is currently no means of tracking historical bioavailable Hg, a substrate for the production of toxic and bioaccumulative methylmercury. This critical knowledge gap potentially hinders policy development, because effective risk reduction strategies depend on a comprehensive understanding of not only present, but also past effects of contaminants on ecosystems. To address this issue, we hypothesized that microbial DNA stored in environmental archives and encoding for Hg detoxification determinants, such as the mercuric reductase gene (merA), can be used to evaluate historical deposition of bioavailable Hg. For this, we recovered and analyzed DNA in dated sediment cores from nine freshwater environments in both Canada and Finland. We found that regardless of Hg loading or latitude, the effective population size of merA started to increase sharply from, on average 1783.8 ± 3.9 CE, coinciding with the onset of the Industrial Revolution. Our results demonstrate that even low levels of globally distributed anthropogenic pollutants, such as mercury, can affect the evolutionary trajectory of microbes inhabiting freshwater ecosystems, and that this evolutionary signal can be used to track historical pollutant bioavailability.