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Holly Rucker

@hollyrucker.bsky.social

PhD candidate at UW-Madison // interested in astrobiology, geobiology, isotopes, and Precambrian Earth

34 Posts116 Follower118 Folgt
Kaçar Lab at UW-Madison@kacarlab.bsky.social · last wk.

Go, Holly! @hollyrucker.bsky.social, one of the main organizers of the 2026 NASA astrobiology graduate student conference! Checkout Holly's awesome paper from earlier this year 💪 www.nature.com/articles/s41...

Resurrected nitrogenases recapitulate canonical N-isotope biosignatures over two billion years - Nature Communications

The study shows that nitrogenase enzymes have maintained stable isotope signatures over billions of years, revealing how ancient microbes shaped Earth’s nitrogen cycle and offering a new experimental ...

nature.com

Astrobiology@astrobiology.bsky.social · last wk.

astrobiology.com/2026/10/22/e... #astrobiology #AbGradCon #AbGradCon26 #NASA @NASAScience_

Kaçar Lab at UW-Madison@kacarlab.bsky.social · 4mo ago

New preprint! How do you engineer one of biology’s most complex enzymes without breaking it? We used evolution as a guide to map a protein interface in nitrogenase, screening >9,000 variants to reveal sequence-function rules for future nitrogen fixation engineering. www.biorxiv.org/content/10.6...

Evolution-guided engineering of an ancient nitrogenase interface enhances enzyme activity and stability

Nitrogenase is the only enzyme capable of biological nitrogen fixation and a major target for sustainable agricultural engineering, yet its functional and structural complexity has made it difficult t...

biorxiv.org

Holly Rucker@hollyrucker.bsky.social · 5mo ago

Just finished this book and absolutely loved it! A very insightful look into the complicated history of taxonomy. I wasn’t familiar with Georges-Louis Leclerc, Comte de Buffon before this book and I’m so glad I am now!

Bild
Kaçar Lab at UW-Madison@kacarlab.bsky.social · 6mo ago

Latest paper out in Nature Communications! We find molecular dating evidence that life was using molybdenum and tungsten as far back as ~3.4 billion years ago, reshaping how we think about trace metals and early microbial evolution. Read here: www.nature.com/articles/s41...

Biological use of molybdenum and tungsten stems back to 3.4 billion years ago - Nature Communications

The study shows that life began using molybdenum and tungsten enzymes as early as 3.7–3.1 billion years ago. Study reveals that key metabolic processes arose despite scarce metals and highlighting the...

nature.com

Morgan Sobol@msobol.bsky.social · 7mo ago

🚨New pub is live! It was really fun to write this with my friend @carolinamicro.bsky.social. If you're curious about how phylogenomics has shaped our understanding of early life and want guidance on how to do this kind of work yourself, then this review is for you. Enjoy! 🚀 doi.org/10.1093/jamb...

Tracing ancient life through the genomic record

Abstract. Since its origins, life has been profoundly interconnected with Earth’s history. The genomes that underpin the diversity of modern life forms hav

doi.org

Kaçar Lab at UW-Madison@kacarlab.bsky.social · 9mo ago

New paper! Why are some Nitrogen fixing microbes more complex? @msobol.bsky.social et al. find that microbes with more N2-fixation genes have larger, more versatile genomes, showing how changing environments shaped this key metabolism! > academic.oup.com/ismecommun/a... @isme-microbes.bsky.social

Ecological constraints and evolutionary trade-offs shape nitrogen fixation across habitats

Abstract. From its earliest beginnings, life’s expansion into new habitats has been profoundly shaped by its reciprocal interactions with Earth’s changing

academic.oup.com

Kaçar Lab at UW-Madison@kacarlab.bsky.social · 9mo ago

Our latest paper on ancient microbes and nitrogen is featured on the NASA website today! 🚀🔬Way to go, @hollyrucker.bsky.social! Resurrecting Ancient Enzymes in NASA’s Search for Life Beyond Earth www.nasa.gov Paper link: www.nature.com/articles/s41... #astrobiology @uwmadscience.bsky.social

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Kaçar Lab at UW-Madison@kacarlab.bsky.social · 9mo ago

Our new paper, out today! We resurrected ancient nitrogenases first used by life on Earth 3 billion years ago. We combined synthetic biology and geology & validated their chemical #biosignature in rocks that helps reveal ancient life on Earth!(and beyond!) Link: www.nature.com/articles/s41...

Resurrected nitrogenases recapitulate canonical N-isotope biosignatures over two billion years - Nature Communications

The study shows that nitrogenase enzymes have maintained stable isotope signatures over billions of years, revealing how ancient microbes shaped Earth’s nitrogen cycle and offering a new experimental ...

nature.com

Holly Rucker@hollyrucker.bsky.social · 9mo ago

Happy to share that a fantastic article about my latest research was just published on NASA’s website! Very grateful to have such a spotlight on my PhD research and recent Nature Communications paper.

Resurrecting Ancient Enzymes in NASA's Search for Life Beyond Earth - NASA Science

NASA-supported scientists have resurrected an enzyme first used by organisms on Earth 3.2-billion years ago and, in the process, have validated a chemical

science.nasa.gov

Holly Rucker@hollyrucker.bsky.social · 10mo ago

IsoCamp was one of the most rewarding experiences of my PhD thus far-I highly recommend it for anyone interested in stable isotopes!

IsoCamp at UNM@isocampunm.bsky.social · 10mo ago

We are now accepting applications for #IsoCamp2026! Join us in beautiful New Mexico June 15th-26th to learn about stable isotopes from expert instructors and get hands-on instrument training. The application deadline is February 28th. For more information, or to apply, go to isocamp.org. Pls share!

Kaçar Lab at UW-Madison@kacarlab.bsky.social · last yr.

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...

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

biorxiv.org