ORIGINAL RESEARCH article
Front. Microbiol.
Sec. Extreme Microbiology
Volume 16 - 2025 | doi: 10.3389/fmicb.2025.1642998
This article is part of the Research TopicAI and Omics Approaches to Microbial Interactions: Applications for Space and EarthView all articles
Growth, physiology and metabolism of Halomonas meridiana in aqueous ammonium sulphate with implications for icy moon astrobiology
Provisionally accepted
- 1The University of Edinburgh UK Centre for Astrobiology, Edinburgh, United Kingdom
- 2The University of Edinburgh School of GeoSciences, Edinburgh, United Kingdom
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The discovery of extraterrestrial reservoirs of liquid water has motivated missions to icy moons Europa and Titan. Tentative evidence of ammonium sulphate (NH4)2SO4 has been detected on the surface of Europa, and (NH4)2SO4 could be a prominent constituent of the Titan subsurface ocean. While NH4+ acts as a nitrogen source for many organisms, detrimental impacts of (NH4)2SO4 fertilizer have been documented in bacteria. Consequently, the presence of (NH4)2SO4 within icy moon environments may constraint the capacity of these environments to support life. In this study, the bacterial survival limits and physiological response to aqueous (NH4)2SO4 were assessed using the extremophile Halomonas meridiana Slthf1. Growth assays demonstrated concentrations exceeding 0.25 M (NH4)2SO4 led to a measurable slowing of the growth rate. Cell density remained comparable to control conditions up to 0.75 M (NH4)2SO4 at which a decline was observed. Contrary to existing hypotheses, alterations to cell density were not determined by pH, osmolarity, salinity, ionic strength, or water activity of the aqueous (NH4)2SO4 solution. Furthermore, neither NH₄⁺ nor SO₄²⁻ alone accounted for these alterations. Metabolite profiling revealed that exposure to (NH4)2SO4 reduced the abundance of glutamine compared to control, indicating an alteration to nitrogen, carbon, and energy metabolism. Active catabolism was suggested by reduced levels of purine metabolites and amino acids. Metabolites within the methylaspartate cycle were detected. We discuss these results with regards to the potential for habitability in aqueous extraterrestrial (NH4)2SO4 environments as well as terrestrial environments in which (NH4)2SO4 fertilizer is applied.
Keywords: ammonium, Ammonium sulphate, Icy Moons, Europa, Titan, habitability, extremophiles, pollution
Received: 07 Jun 2025; Accepted: 25 Aug 2025.
Copyright: © 2025 Hopton, Nienow and Cockell. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Cassie Marie Hopton, The University of Edinburgh UK Centre for Astrobiology, Edinburgh, United Kingdom
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