Widespread detoxifying NO reductases impart a distinct isotopic fingerprint on N2O under anoxia

• 成果类型: Article
• 署名作者: Wang, Renee Z.; Lonergan, Zachery R.; Wilbert, Steven A.; Eiler, John M.; Newman, Dianne K.
• 署名单位: California Institute of Technology; California Institute of Technology; Johns Hopkins University
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-9099
• DOI: 10.1073/pnas.2319960121
• 发表日期: 2024-06-18
• 关键词: coli flavohaemoglobin hmp; nitrous-oxide; nitric-oxide; bacterial; flavohemoglobin; isotopomers; signatures; responses; dioxygen; binding

摘要

Nitrous oxide (N2O), a potent greenhouse gas, can be generated by multiple biological and abiotic processes in diverse contexts. Accurately tracking the dominant sources of N2O has the potential to improve our understanding of N2O fluxes from soils as well as inform the diagnosis of human infections. Isotopic Site Preference (SP) values have been used toward this end, as bacterial and fungal nitric oxide reductases (NORs) produce N2O with different isotopic fingerprints, spanning a large range. Here, we show that flavohemoglobin (Fhp), a hitherto biogeochemically neglected yet widely distributed detoxifying bacterial NO reductase, imparts a distinct SP value onto N2O under anoxic conditions (similar to+10 parts per thousand) that correlates with typical environmental N2O SP measurements. Using Pseudomonas aeruginosa as a model organism, we generated strains that only contained Fhp or the dissimilatory NOR, finding that in vivo N2O SP values imparted by these enzymes differ by over 10 parts per thousand. Depending on the cellular physiological state, the ratio of Fhp:NOR varies significantly in wild-type cells and controls the net N2O SP biosignature: When cells grow anaerobically under denitrifying conditions, NOR dominates; when cells experience rapid, increased nitric oxide concentrations under anoxic conditions but are not growing, Fhp dominates. Other bacteria that only make Fhp generate similar N2O SP biosignatures to those measured from our P. aeruginosa Fhp-only strain. Fhp homologs in sequenced bacterial genomes currently exceed NOR homologs by nearly a factor of four. Accordingly, we suggest a different framework to guide the attribution of N2O biological sources in nature and disease.