Biology subjects

Oehlmann, N. N.

Publications and source records attributed to Oehlmann, N. N..

4 recordsLinked to original sources

bioRxiv2026

Farming and climate legacies shape the seed microbiota and offspring drought responses in wheat

Seeds link parental environments to offspring establishment, but whether seed-associated bacteria retain signatures of farming and climate legacies across plant generations remains unclear. Here, we characterized epiphytic and endophytic bacterial communities of winter wheat seeds collected from the Global Change Experimental Facility (GCEF) in Germany across three harvest years representing contrasting climates. We then tested how farming (organic versus conventional) and climate (ambient versus future) legacies experienced by maternal plants were associated with offspring rhizosphere bacterial communities and plant performance under drought in the greenhouse. Harvest year was the dominant driver of grain dry weight and seed-associated bacterial communities. Climate legacy additionally affected seed epiphytic communities, whereas farming legacy was expressed in the endophytic diversity. Germination was higher overall for seeds from the conventional than the organic farming legacy and from the ambient than the future climate legacy. A small subset of unique seed-associated ASVs was detected in offspring rhizospheres. Although these ASVs occurred at low relative abundance in seeds (<1%), they accounted for up to approximately 40% of rhizosphere relative abundance under drought. Together, these findings show that seeds retain bacterial signatures of parental farming and climate legacies and that a subset of seed-associated ASVs remains detectable and can become abundant in offspring rhizospheres under drought.

microbiology↗

bioRxiv2026

Directed evolution of the Fe-nitrogenase for CO2 reduction to hydrocarbons

The iron (Fe) nitrogenase drives bacterial methane (CH4) formation by converting carbon dioxide (CO2) to CH4 in a single enzymatic step. Enhancing the initial CH4 formation activity of Fe-nitrogenase and expanding the product spectrum to hydrocarbon chains could lead to a route for sustainable feedstock chemicals. Here, we performed the first directed evolution campaign on the Fe-nitrogenase aimed at optimizing the hydrocarbon production. We achieved an [~]8-fold increase in CH4 formation by Fe-nitrogenase expressing Rhodobacter capsulatus cultures in three rounds of site-saturation mutagenesis. The best performing mutant (F362ManfD, Y85FanfD, T360SanfD) extends the in vivo product spectrum of the nitrogenase to ethane (C2H6) and exhibits 6-fold higher rates for CO production in vitro, whereas the formation of the undesirable byproduct formate was abolished. Electron microscopy-based structural analysis identified a methionine and water potentially stabilizing the transition state and fine-tuning the CO2 reduction mechanism and activity.

biochemistry↗

bioRxiv2023

CO2 Reduction by the Iron Nitrogenase Competes with N2 Fixation Under Physiological Conditions

Nitrogenases are the only known enzymes that reduce molecular nitrogen (N2) to ammonia. Recent findings have demonstrated that nitrogenases also reduce the greenhouse gas carbon dioxide (CO2), suggesting CO2 to be a competitor of N2. Intriguingly, nitrogenase isoforms (i.e., molybdenum (Mo), vanadium and iron (Fe) nitrogenase) differ significantly in their ability to reduce CO2, but the mechanisms underlying these differences remain elusive. Here, we study the competing reduction of CO2 and N2 by the two nitrogenases of Rhodobacter capsulatus, the Mo and Fe nitrogenase. Analyzing their full CO2 reduction product spectrum in vitro, we find the Fe nitrogenase almost three-fold more efficient in CO2 reduction than the Mo isoform. Furthermore, the in vitro competition experiments reveal the Fe nitrogenase to be profoundly less selective for the reduction of N2 than the Mo nitrogenase. We observe the same effects in vivo, where adding CO2 drastically increases the doubling times of diazotrophically grown R. capsulatus strains that rely on the Fe nitrogenase. The Fe nitrogenase-dependent R. capsulatus strains reduce CO2 to methane under physiological conditions, highlighting the potential of the Fe nitrogenase for the biotechnological conversion of CO2 into value-added compounds. Furthermore, both products are secreted into the surrounding, potentially influencing the composition of microbial communities in Mo-deficient environments.

biochemistry↗

bioRxiv2023

Structural Insights into the Iron Nitrogenase Complex

Nitrogenases are best known for catalysing the reduction of dinitrogen to ammonia at a complex metallic cofactor. Recently, nitrogenases were shown to reduce carbon dioxide (CO2) and carbon monoxide to hydrocarbons, offering a pathway to recycle carbon waste into hydrocarbon products. Among the nitrogenase family the iron nitrogenase is the isozyme with the highest wildtype activity for the reduction of CO2, but the molecular architecture facilitating these activities remained unknown. Here, we report a 2.35-[A] cryogenic electron microscopy structure of the Fe nitrogenase complex from Rhodobacter capsulatus, revealing an [Fe8S9C-(R)-homocitrate]-cluster in the active site. The enzyme complex suggests that the AnfG-subunit is involved in cluster stabilisation, substrate channelling and confers specificity between nitrogenase reductase and catalytic components. Moreover, the structure highlights a different interface between the two catalytic halves of the iron and the molybdenum nitrogenase, potentially influencing the intra-subunit communication and thus the nitrogenase mechanism.

biochemistry↗