Nitrogen fixation mechanisms and distribution patterns of UCYN-A in the global ocean

Nitrogen fixation mechanisms and distribution patterns of UCYN-A in the global ocean | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Biological Sciences - Article Nitrogen fixation mechanisms and distribution patterns of UCYN-A in the global ocean Subhendu Chakraborty, Jonathan Zehr, Ondřej Prášil, Wing Mak, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5545073/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Biological N2 fixation is fundamental for supporting life on our planet1. UCYN-A, previously classified as unicellular cyanobacterium, shows molecular characteristics of an early-stage N2-fixing organelle, or nitroplast2, inside the haptophyte cell Braarudosphaera bigelowii and appears to be one of the most abundant3 and important4,5 N2-fixers in the global ocean. However, the mechanisms underpinning N2 fixation in B. bigelowii/UCYN-A and its geographic distribution remain unclear. Here we use new experimental observations and literature data in combination with a novel cell-based metabolic model to explain the intracellular pathways governing N2 fixation of B. bigelowii/UCYN-A and how these pathways determine its global biogeography. Our model shows that B. bigelowii/UCYN-A can fix N2 at low light and over a broad range of temperatures, explaining the ubiquitous distribution of this organism also in relatively deep waters and at high latitudes. We find high surface N2 fixation rates almost everywhere in the Atlantic and Indian Oceans but not in the Pacific Ocean, where N2 fixation is limited to specific regions. Our results indicate that B. bigelowii/UCYN-A is a key player in the oceanic nitrogen cycle, especially in nutrient-limited regions of the oceans, and shed new light on the role this microorganism may play in marine ecosystems. Biological sciences/Ecology/Ecological modelling Biological sciences/Ecology/Theoretical ecology Biological sciences/Ecology/Microbial ecology Full Text Additional Declarations There is NO Competing Interest. Supplementary Files UCYNA20241128supp.pdf Supplementary File Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5545073","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Biological Sciences - Article","associatedPublications":[],"authors":[{"id":400550204,"identity":"4cbe3e09-7115-4141-9273-55b724a09635","order_by":0,"name":"Subhendu 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UCYN-A, previously classified as unicellular cyanobacterium, shows molecular characteristics of an early-stage N2-fixing organelle, or nitroplast2, inside the haptophyte cell Braarudosphaera bigelowii and appears to be one of the most abundant3 and important4,5 N2-fixers in the global ocean. However, the mechanisms underpinning N2 fixation in B. bigelowii/UCYN-A and its geographic distribution remain unclear. Here we use new experimental observations and literature data in combination with a novel cell-based metabolic model to explain the intracellular pathways governing N2 fixation of B. bigelowii/UCYN-A and how these pathways determine its global biogeography. Our model shows that B. bigelowii/UCYN-A can fix N2 at low light and over a broad range of temperatures, explaining the ubiquitous distribution of this organism also in relatively deep waters and at high latitudes. We find high surface N2 fixation rates almost everywhere in the Atlantic and Indian Oceans but not in the Pacific Ocean, where N2 fixation is limited to specific regions. 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