Tectonically-driven oxidant production in the hot biosphere

Earth is a tectonically active planet, and subsurface faults and fractures provide habitats for microbial ecosystems in continental crust, ocean crust, and overlying ocean sediment. Importantly, the fracturing of silicate rocks along faults can split water via mechanochemical reactions (Kita et al., 1982) and this hydrogen cab be used to support subsurface life (Hirose et al., 2011; Parkes et al., 2011; Telling et al., 2015). However, the ultimate fate of the oxygen from the water splitting has remained enigmatic. Recent experiments in our laboratory have shown that at temperatures <80°C the oxygen equivalents remain stable as defects on mineral surfaces, but at hotter temperatures (which coincide with the temperature growth range for hyperthermophiles; the most heat-loving microorganisms) these oxidants are released (Stone et al., 2022). This release of oxygen from water provides a mechanism for reactive oxygen production in the tectonically active subsurface prior to the advent of photosynthesis, and may have helped drive the (bio)geochemistry of hot fractures where life first evolved (Stone et al., 2022). This PhD studentship will carry out a series of novel experiments linked to fieldwork in Iceland to investigate the importance of mechanochemical reactions for supporting microbial life in the subsurface, from present day to deep past. The studentship links into the 3 year standard NERC grant CERBERUS (https://research.ncl.ac.uk/cerberus/).

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Image Captions

Hot springs – windows into the deep hot biosphere (Photo J. Telling)


i. Conduct laboratory experiments (both with and without microbial inocula) on a range of crushed natural minerals and rocks using a gastight planetary ball mill, pressure vessels, and microcosms. Changes in inorganic and organic chemistry aqueous and solid phase chemistry, and dissolved gases, will be analyzed via a range of methods including ion chromatography, UV-vis spectrometry, and gas chromatography/mass spectrometry. Changes in microbial community will be assessed through comparisons of 16S rRNA diversity, metagenome analysis, and expression of mRNA.
ii. Collect natural environmental samples of hyperthermophilic microbial communities from hot springs in Iceland to use in above experiments, and measure concentrations of mechanochemical products in the field linked to seismic activity
iii. Use geochemical thermodynamic and kinetic modelling to model the mechanochemical reactions and calculate the potential energy generated to support life.
iv. Statistical analysis/synthesis. Relevant statistical methods (e.g. ANOVA, regression analysis, PCA analysis) will be used to assess the significance of results. Results will be synthesized with existing literature.

Project Timeline

Year 1

Literature review, pilot experiments, initial mineral experiments, Iceland field sampling. Training in geochemical techniques and kinetic/thermodynamic modelling.

Year 2

Further experiments focused on assessing role of pressure on abiotic products of reactions. Training in kinetic and thermodynamic modelling. Training in microbiology techniques and bioinformatics. Attend UK conference. Prepare manuscript.

Year 3

Iceland sampling. Final experiments assessing the potential of high temperature mechanochemical reactions to support microbial growth. Attend international conference. Prepare manuscript.

Year 3.5

Write up final thesis, prepare manuscript.

& Skills

Newcastle University has a faculty-run postgraduate training programme that follows the Vitae Researcher Development Framework (http://www.vitae.ac.uk/). Each PhD student has a tailor-made Personal Development Plan, with the expectation of them taking 60 credits in the first year and 40 credits in the second year covering both specific skills required for the project (e.g. analytical methodology, statistical analysis) and transferable skills. The candidate will also gain expertise in the use of specialised experimental apparatus, geochemical analyses, molecular biology and bioinformatics, biogeochemical interpretation, and core research skills such as experimental design, fieldwork planning, data analysis and scientific writing.

References & further reading

Kita, I., Matsuo, S. & Wakita, H. H2 generation by reaction between H2O and crushed rock: an experimental study on H2 degassing from the active fault zone. Journal of Geophysical Research: Solid Earth 87, 10789-10795 (1982).
Hirose, T., Kawagucci, S. & Suzuki, K. Mechanoradical H2 generation during simulated faulting: Implications for an earthquake‐driven subsurface biosphere. Geophysical research letters 38 (2011).
Parkes, R. J. et al. Prokaryotes stimulate mineral H2 formation for the deep biosphere and subsequent thermogenic activity. Geology 39, 219-222 (2011).
Stone, J. et al. Tectonically-driven oxidant production in the hot biosphere. Nature Communications 13, Article number 4529 (2022)
Telling, J. et al. Rock comminution as a source of hydrogen for subglacial ecosystems. Nature Geoscience 8, 851-855 (2015).

See also CERBERUS website (https://research.ncl.ac.uk/cerberus/).

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