Swift evolutionary response of microbes to a rise in anthropogenic mercury in the Northern Hemisphere

Abstract

Anthropogenic mercury remobilization has considerably increased since the Industrial Revolution in the late 1700s. The Minamata Convention on Mercury is a United Nations treaty (2017) aiming at curbing mercury emissions. Unfortunately, evaluating the effectiveness of such a global treaty is hampered by our inability to determine the lag in aquatic ecosystem responses to a change in atmospheric mercury deposition. Whereas past metal concentrations are obtained from core samples, there are currently no means of tracking historical metal bioavailability or toxicity. Here, we recovered DNA from nine dated sediment cores collected in Canada and Finland, and reconstructed the past demographics of microbes carrying genes coding for the mercuric reductase (MerA)-an enzyme involved in Hg detoxification-using Bayesian relaxed molecular clocks. We found that the evolutionary dynamics of merA exhibited a dramatic increase in effective population size starting from 1783.8 ± 3.9 CE, which coincides with both the Industrial Revolution, and with independent measurements of atmospheric Hg concentrations. We show that even low levels of anthropogenic mercury affected the evolutionary trajectory of microbes in the Northern Hemisphere, and that microbial DNA encoding for detoxification determinants stored in environmental archives can be used to track historical pollutant toxicity.

Warming Climate Is Reducing the Diversity of Dominant Microbes in the Largest High Arctic Lake

“…Adequate DNA concentrations for sequencing were reached by combining triplicate extractions for a total volume of 45 μl and a concentration ≥ 50 ng/μl ( Supplementary Table 7 ). Positive and negative controls were used to verify the integrity of the PCR amplification of glnA (see also Ruuskanen et al, 2020 ). Two kit extraction blanks contained no trace of DNA and were not sequenced.…”

Lake Sedimentary DNA Research on Past Terrestrial and Aquatic Biodiversity: Overview and Recommendations

“…A study succeeded in tracing within-population genetic variation in an algae population during the Last Glacial Maximum [81]. The presence of key functional sets of genes from aquatic organisms can also be traced using the sedaDNA approach, like in the case of mcy genes responsible for producing microcystin by specific cyanobacteria [89,90], amoA genes associated with ammonia oxidation [91] and merA genes involved in mercury detoxification [92,93]. Finally, the research works showed how it is possible to study past activity of methanotrophs in lake systems [66,[94][95][96][97].…”

Common physiological processes control mercury reduction during photosynthesis and fermentation

“…In addition to gene deletions, whole-genome, transcriptome, and proteome approaches could be combined with isotopic analyses in pure cultures to hone in on potential biomarkers for Hg transformation pathways that remain poorly understood. Such biomarkers could be used to examine publicly available genomic datasets to assess the distribution of anaerobic Hg reducers in modern day environments and rock records, the latter serving as an archive for Hg isotope signatures and the microbial community involved in historical Hg cycling (31,58). These ancient environments were likely dominated by anoxygenic phototrophs that were important primary producers before the rise of oxygen on Earth.…”