Date of Graduation

8-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Cell & Molecular Biology (PhD)

Degree Level

Graduate

Department

Cell & Molecular Biology

Advisor/Mentor

Ivey, D. Mack

Committee Member

McNabb, David S.

Second Committee Member

Erf, Gisela F.

Third Committee Member

Lessner, Daniel J.

Keywords

Astrobiology; Bacterial metabolism; Desulfotalea psychrophila; Geobiology; Mars; Psychrophile; Sulfate reduction

Abstract

Since ancient times, Humanity has been fascinated with the idea of what lies beyond the borders of our planet. Fortunately, the combined efforts of many nations have made it possible to send unmanned spacecraft to orbit planets located close to Earth. These missions have the principal goal to collect data that could help us understand the basic environmental conditions that persist on those planets, or for evidence of past or present life. Equally important, landers and rovers have been successfully deployed to start the in-situ exploration of many planets of the Solar System. Among them, Mars has been extensively studied due to its closeness with Earth, and because it is located within the habitable zone. Many hypotheses about the presence of current microbial life in this planet have been formulated. However, a definite answer is still elusive. In this research, we have tested the ability of a psychrophilic bacterium, Desulfotalea psychrophila (D. psychrophila), to survive and proliferate at subfreezing temperatures and at increasing concentrations of sulfate minerals known to be present in the Martian regolith and icy satellites from the Jovian and Saturn Systems. We have found that D. psychrophila cells can survive and proliferate, at least temporarily, at temperatures down to -5 °C and -10 °C in which sulfate compounds, specially MgSO4 and CaSO4, induced a combined effect of chaotropicity and physical protection against mechanical damage of the cellular membrane allowing these bacterial cells to metabolize at suboptimal temperatures. Furthermore, our studies have shown evidence of the importance of metabolic specialization in which bacterial cells from the same clonal population can react differently by prioritizing maintenance, growth, or both when challenged with temperatures below their optimal growth temperature. This type of investigation is relevant to the field of Astrobiology because it facilitates the identification of the lower boundaries of cold temperatures that could permit the development of metabolic processes in planets or satellites other than our own.

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