Biology subjects

Cockell, C. S.

Publications and source records attributed to Cockell, C. S..

3 recordsLinked to original sources

bioRxiv2026

Defined Mars Media (DMM), a chemically defined simulant of the soluble macro- and micro- nutrients in Mars regolith for use in biological research

Mars harsh yet workable surface conditions, such as manageable temperatures, availability of solar energy, and in situ resources like water ice, carbon dioxide, and mineral-rich regolith, make it a compelling target for supporting life beyond Earth. However, existing experiments testing chemical habitability in Mars conditions generally rely on leachates of physical regolith simulants, which vary in composition across simulant types, leaching conditions, and production batches. We introduce a defined Mars media (DMM) that accurately simulates the biologically relevant nutrients (nitrogen, phosphorus, and sulfur) and stressors (perchlorates, heavy metals) in Martian regolith when it is leached in water at neutral pH. We formulated DMM by combining direct rover and lander measurements from Mars with laboratory measurements of regolith simulant leachates. We validate DMM from a 1x to 20x concentrate, equivalent to 40 g/L to 800 g/L of leached regolith. Using DMM with acetate as a Mars atmosphere-derived carbon source, we grew eight bacteria, demonstrating that organisms can source all essential nutrients from Martian resources. We also demonstrate that microbial growth in DMM is robust to uncertainties in Martian regolith composition: sensitivity experiments can identify limiting trace element nutrients and toxins in DMM, and show that bacterial growth is maintained across at least an order of magnitude variation in their concentrations. This is the first defined Mars regolith media recipe containing both macro- and micro-nutrients, and designed specifically for biological experimentation. By shifting from variable leachate-based approaches to a defined aqueous analog, we enable controlled hypothesis testing of microbial survival, growth, and function in a Martian chemical environment. DMM will enable further research on astrobiology, biological in situ resource utilization, large-scale soil remediation, and terraforming. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=121 SRC="FIGDIR/small/719001v2_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@37408forg.highwire.dtl.DTLVardef@16fabfforg.highwire.dtl.DTLVardef@84fa43org.highwire.dtl.DTLVardef@4a7c5e_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2025

High pressures depress the onset of intracellular vitrification

The low temperature limit for life remains elusive and poorly understood. This ignorance is further compounded when applied to life in multi-extreme environments where low temperatures combine with factors such as high salt concentrations, or high environmental pressures. It has been proposed that the onset of intracellular vitrification enforces a biophysical low temperature limit for unicellular life at [~] -23 {degrees}C. However, it has not been demonstrated how high-pressures affect intracellular vitrification, which is vital for understanding the habitability of low temperature, subsurface environments, both on Earth and on other planetary bodies. Here, we used high-pressure differential scanning calorimetry to measure the intracellular vitrification of Bacillus subtilis across pressures ranging from 1 to 1000 bar. We find that high pressures depress the onset of intracellular vitrification in a pressure dependent manner, which is tightly correlated with the ability of pressure to depress the freezing point of water. Additionally, we show that sub-molar concentrations of NaCl can act in combination with high pressures to further depress intracellular vitrification, highlighting the interplay between temperature, pressure, and ions in influencing the physical state of cells in natural environments. These results show that cells in subzero high-pressure environments would be liquidous, and potentially metabolically active, and not merely vitrified and preserved. Additionally, our results provide considerations in the preparation of biological samples through high-pressure freezing for electron microscopy, particularly those associated with high concentrations of cryoprotectants.

microbiology↗

bioRxiv2017

Biofilms Confer Resistance to Simulated Extra-terrestrial Geochemical Extremes

1AO_SCPLOWBSTRACTC_SCPLOWBiofilms improve microbes resistance to a variety of extreme physical and chemical conditions on Earth. The discovery of putative aqueous environments on other planetary bodies such as Mars motivates an interest in understanding the viability of life, and the potential role of biofilms, in previously unexplored geochemical extremes. We investigated the loss of viability of planktonic cells and biofilms of Sphingomonas desiccabilis (a Gram-negative, desiccation resistant, soil crust-forming organism) to simulated Martian brines. These brines were produced from geochemical modelling of past aqueous environments on Mars, and their high sulfate concentrations make them different to most terrestrial brines, although similar briny environments have been found in locations such as the Basque Lakes in Canada or in deep subsurface groundwater systems. Biofilms grown on basaltic scoria were subjected to the simulated martian brines and the viability of cells was measured over time and compared to equivalent planktonic cultures. Crystal violet assay was used to measure how the biomass of the biofilms changed over time in response to the brines. While certain brines were highly hostile to microbial viability, we found that biofilms that were desiccated prior to being treated with brines maintained viability over a longer treatment period when compared to planktonic cells. Our results show that biofilms confer short-term protection to the harsh osmotic, ionic, and acidic conditions of Mars-relevant brines. However, in the most extreme simulated brines, even biofilms eventually lost viability. By demonstrating that biofilms confer protection to conditions that are potentially analogous to current day recurrent slope lineae (thought to be produced by the flow of briny fluids) on Mars, our results show that contaminant biofilm-forming microorganisms may have a greater chance of surviving in so-called Special Regions on Mars, with implications for planetary protection in missions that aim to explore these regions.

microbiology↗