Check out the summary on my laboratory website as well: sites.uwm.edu/petersob/202....

Check it out, and let me know what you think! This represented a major effort from a large team, and I'm proud to see this work out in the world.

Overall transcriptional activity was also higher in SRB. However, we also identified an arsR-like transcriptional regulator preceding hgcA (previously reported, see text for ref.); these elements were associated with lower hgcA expression and found more frequently in the non-SRB methylators.

Inhibition of sulfate-reducing bacteria using molybdate resulted in a drastic decrease in MeHg production across all redox conditions. Surprisingly, sulfate-reducing bacteria (SRB) only accounted for <10% of the hgcA gene abundance, but represented the majority (>50%) of the hgcA gene transcription.

We investigated microbial drivers of methylation using metagenomic and metatranscriptomic sequencing, targeting the mercury-methylating gene hgcA. Gene abundance of hgcA also increased with sulfide, but hgcA expression peaked along with the rate potential, at moderate sulfide concentrations.

Methylation rate potentials were high, reaching 0.165 day-1. Generally, rate potentials increased with increasing sulfide. Paired methylation and demethylation rates, combined with Hg speciation, strongly suggests that in situ methylation is the primary source of methylmercury in the water column.

We designed a method for conducting enriched stable isotope Hg transformations assays under in situ conditions using custom-designed trace-metal clean bags resuspended in the lake for the duration of the incubation. This was a labor of love... the first trial assays were conducted in 2017!

Lake Mendota is a well-studied and eutrophic lake with an anoxic hypolimnion for most of the stratified year. Methylmercury concentrations can reach up to 80% (!!!) of total mercury in the hypolimnion, and sulfate reduction appears to be a key pathway driving microbial metabolism.

As projects develop, I will be looking to recruit graduate students, undergraduates, and postdocs starting in 2025. If you or someone you know is interested in any or all of these topics, stay tuned for these opportunities!

My lab will focus on contaminant and microbial biogeochemistry, with a specific emphasis on mercury and the Great Lakes region. We will be highly collaborative and use an interdisciplinary approach, with research programs in both environmental and culture-based study systems.