Anne Dekas

Microbial N2O reduction in sulfidic waters: Implications for Proterozoic oceans Throughout Earth’s history, shifts in ocean redox influenced the bioavailability of trace metals, shaping the activity of microorganisms. In Proterozoic oceans, the precipitation of copper (Cu) with sulfide was hypothesized to limit the bioavailability of Cu. This limitation may have suppressed microbial reduction of nitrous oxide (N2O), due to the Cu dependency of nitrous oxide reductase (Nos). It is thought that without this critical microbial sink, Proterozoic oceans were a significant net source of N2O. Here, we revisit this paradigm in light of recently derived ∼20-fold lower estimates for sulfide in Proterozoic seawater and an empirical evaluation of the potential for microbial N2O reduction under sulfidic conditions. Leveraging publicly available environmental metatranscriptomes, we infer active N2O reduction from the detection of nosZ transcripts in multiple marine and lacustrine systems in which sulfide and Cu concentrations are analogous to those of the Proterozoic. In controlled culture experiments, we demonstrate that the purple non-sulfur bacterium Rhodopseudomonas palustris can reduce N2O at sulfide concentrations up to 100 µM, well above levels predicted for Proterozoic oceans. Based on trace metal speciation modeling, we suggest that Cu remains bioavailable under Proterozoic-like conditions as a dissolved CuHS complex. Using phylogenetics, we infer that early N2O reducers were probably anoxygenic phototrophs and performed N2O reduction as dark metabolism. Collectively, these observations suggest microbial N2O reduction occurs under euxinic conditions, implying that Proterozoic marine N2O emissions were substantially lower than previously proposed. Our conclusions inform our understanding of the microbial ecology in sulfidic waters, the early climate, and the search for extraterrestrial life. ### Competing Interest Statement The authors have declared no competing interest. National Aeronautics and Space Administration, https://ror.org/027ka1x80, 80NSSC17K0296

New preprint on ancient oceans!

We challenge the idea of early Earth as major N2O source; reshaping views on climate & biosignatures. Led by S. Buessecker @annedekas.bsky.social lab!

➡️ Microbial N2O reduction in sulfidic waters: Implications for Proterozoic oceans
www.biorxiv.org/content/10.1...

07.07.2025 16:31 — 👍 15    🔁 7    💬 0    📌 0

Follow along with PhD student Jessica Bullington on a research cruise off the coast of San Francisco, part of an effort to study microorganisms in the deep sea led by @annedekas.bsky.social ⬇️

11.07.2025 19:58 — 👍 2    🔁 1    💬 1    📌 0

over a year later, this one out today!

link.springer.com/article/10.1...

16.06.2025 16:35 — 👍 34    🔁 15    💬 3    📌 0

Congratulations, Yunha!!! You are so awesome and MIT is so lucky to have you!

29.04.2025 20:02 — 👍 1    🔁 0    💬 0    📌 0

We’re on our way! Sailed under the Golden Gate Bridge on our first of 14 days at sea. We’re investigating GHG cycling by deep-sea microbes using ‘omics, isotopes, and imaging. #DARCMicrobes #RVSallyRide @stanforddoerr.bsky.social

09.04.2025 03:32 — 👍 5    🔁 0    💬 1    📌 0

Abundance, Identity, and Potential Diazotrophic Activity of nifH‐Containing Organisms at Marine Cold Seeps We pair amplicon sequencing and qPCR of nifH genes and transcripts to assign taxonomy to putative nitrogen-fixers at cold seeps and quantify their abundance. We find and correct for significant numbe...

New paper from my group on the abundance and phylogenetic diversity of nifH genes at deep-sea methane seeps. nifH genes are within 17 phyla at seeps (!) and are up to 1000X more abundant than in nearby sediment. Also, beware overestimates by broad nifH qPCR primers! doi.org/10.1111/1462...

11.03.2025 18:08 — 👍 7    🔁 2    💬 0    📌 0

Unexpected scarcity of ANME archaea in hydrocarbon seeps within Monterey Bay Abstract. Marine hydrocarbon seeps typically harbor a relatively predictable microbiome, including anaerobic methanotrophic (ANME) archaea. Here, we sampled two cold seeps in Monterey Bay, CA – Clam F...

Our most recent paper on methane seeps is out: bg.copernicus.org/articles/22/.... Two seeps in Monterey Canyon have virtually no ANME (methane oxidizers), suggesting an unabated methane flux at these and similar seeps. The microbiological methane filter in sediments is not ubiquitous.

24.01.2025 22:15 — 👍 5    🔁 2    💬 0    📌 0

Cyanobacteria from marine oxygen-deficient zones encode both form I and form II Rubiscos | PNAS Cyanobacteria are highly abundant in the marine photic zone and primary drivers of the conversion of inorganic carbon into biomass. To date, all st...

Hello bluesky world! Happy to be here and looking forward to connecting/re-connecting with you all. I'm excited to share a paper just out today, led by postdoc @alexjaf.bsky.social. Prochlorococcus with two forms of rubisco! www.pnas.org/doi/10.1073/....

25.11.2024 22:14 — 👍 29    🔁 13    💬 1    📌 0