Preservation of extracellular sheaths produced by iron-oxidising bacteria: an analogue for potential morphological biosignatures on Mars
File(s)
Accepted version
Author(s)
Hirsch, S
Tan, Jonathan S
Hickman-Lewis, Keyron
Sephton, Mark A
Type
Journal Article
Abstract
In the search for life on Mars, evaluating the biogenicity of morphological structures may be important as they can provide a primary independent line of evidence for past life, and can be used to target areas to focus further analyses. However, our experience with terrestrial materials indicates that the deleterious effects of diagenetic processes regularly make the assessment, and even detection, of microfossils and other microscopic biosignatures challenging. To improve our understanding of these effects on Mars, we subjected samples containing sheath-shaped extracellular structures produced by iron-oxidising bacteria (FeOB), from a Mars analogue circumneutral iron deposit, to artificial maturation by hydrous pyrolysis. Simulated diagenesis induced a phase change in the mineralogy of the structures, from ferrihydrite to crystalline iron oxides. We find that conditions associated with the onset of this phase change are correlated with the start of significant degradation of the extracellular structures. Our results reveal the sensitivity of remains of iron-oxidising bacteria to diagenesis, providing insights for improved targeting of astrobiological missions to areas on Mars that are most conducive to morphological biosignature preservation. Additionally, these results compel increased scrutiny of FeOB-like purported biosignatures if their mineralogy is dominated by crystalline iron oxides.
Date Issued
2025
Date Acceptance
2024-11-28
Citation
Astrobiology, 2025
ISSN
1531-1074
Publisher
Mary Ann Liebert
Journal / Book Title
Astrobiology
Copyright Statement
Subject to copyright. This paper is embargoed until publication. Once published the author’s accepted manuscript will be made available under a CC-BY License in accordance with Imperial’s Research Publications Open Access policy (www.imperial.ac.uk/oa-policy).
License URL
Publication Status
Accepted
Rights Embargo Date
10000-01-01
Date Publish Online
2025