A Window into the Past of Hg Microbiology
Bibliographic record
Abstract
Mercury (Hg) is a naturally occurring global pollutant that has, since the late 1700s, been increasingly remobilized in the environment by anthropogenic activities.The continued importance of Hg as a chemical of concern to human health was underscored by the recent ratification of the Minamata convention (2017), requiring governments to regulate Hg emissions, reduce Hg mining, supply, trade and waste, to limit its environmental impacts.One area where data is scarce, and which could aid in managing Hg pollution, is in determining the lag in aquatic ecosystem response to a change in atmospheric Hg deposition.Indeed, whereas the total concentration of metals can be determined from environmental archives, there is currently no means of tracking their bioavailable and often toxic, fractions.For Hg in particular, this fraction represents a substrate for the production of toxic methylmercury.To address this issue, we hypothesized that microbial DNA stored in environmental archives and encoding for Hg detoxification metabolism, such as the mercuric reductase gene (merA), can be used to evaluate historical deposition of Hg.We predicted that increasing selective pressure from anthropogenic mercury would affect the evolutionary trajectory of aquatic microbes over broad continental scales and inform on the fraction of bioavailable Hg.For this, we recovered and analyzed DNA in dated sediment cores from Canada and Finland, and reconstructed the past demographics of microbes carrying genes encoding for MerA using models known as Bayesian relaxed molecular clocks.We found that the evolutionary dynamics of merA exhibited a dramatic increase in effective population size at the end of the 18 th century, which coincided with both the Industrial Revolution, and with independent measurements of atmospheric Hg concentrations [1].We show that this evolutionary response was both swift and synchronous across two continents in the Northern Hemisphere.We are cautiously optimistic that applying this approach to study the biological history of other metals, for which detoxification and homeostasis are genetically coded in microbes, will yield new insights into metal cycling.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.005 | 0.006 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.004 | 0.014 |
| Scholarly communication | 0.011 | 0.017 |
| Open science | 0.001 | 0.005 |
| Research integrity | 0.004 | 0.012 |
| Insufficient payload (model declined to judge) | 0.012 | 0.003 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".