A Genome Catalogue of Mercury-Methylating Bacteria and Archaea from \nSediments of a Boreal River Faced by Human Disturbances
Bibliographic record
Abstract
Methylmercury (MeHg), the most bioavailable form of mercury (Hg), is a neurotoxin produced by anaerobic microbes. MeHg generated in aquatic sediments can be transferred to aquatic organisms and biomagnified along food webs, ultimately reaching fish consumers. This is a particular concern for rivers, as they are connective bodies for aquatic ecosystems and play crucial roles in the transport of nutrients. Moreover, rivers exhibit heightened susceptibility to environmental disturbances within their watershed, which have been linked to increased Hg-methylation. Rivers impacted by run-of-river dams hold specific significance, given the growing preference for these dam types over reservoir dams. Early studies have identified sulfate reducers, methanogens, and iron reducers as the main contributors to Hg methylation. More recently, proteins encoded by the hgcAB genes have been found to confer the ability to methylate Hg. Recent metagenomic studies have expanded our knowledge of hgcAB-carrying lineages in the environment. Nevertheless, genome-based exploration of Hg-methylators remains limited, particularly in the context of river systems. To fill this knowledge gap, we created a genome catalogue of Hg-methylating microorganisms from the sediments of a river impacted by two run-of-river dams, logging, and a forest fire. We assessed the taxonomic and metabolic diversity of these putative Hg-methylators. Additionally, we assessed their abundance and diversity across sites along the river that were subject to different disturbances to gain insight into the ecological impact on Hg-methylators. For a deeper understanding of the environmental factors shaping Hg-methylator \ndiversity, we juxtaposed the genome catalogue with the wider microbial community to which these methylators belong. We uncovered a unique and diverse assemblage of Hg-methylators dominated by members of metabolically versatile and fermentative Bacteroidota. This assemblage was particularly enriched in butyrate fermentative, carbon fixing and nitrite reducing microbes. We found that sites affected by press-like disturbances such as logging were particularly favorable to the establishment of a Hg-methylating niche. Lastly, we argue that the effects of watershed disturbances are likely not specific to Hg-methylators, but rather shared across the greater microbial community.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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 teacher head, 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".