Doctoral Dissertations

Orcid ID

0000-0001-7430-7679

Date of Award

5-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Microbiology

Major Professor

Jill A. Mikucki

Committee Members

Alison Buchan, Elizabeth Fozo, Sean Schaeffer

Abstract

Cryosphere microorganisms can provide fundamental insights into individual and community response to a changing climate, and how we may detect past or present life on other planets. The polar desert of the McMurdo Dry Valleys (MDV), the largest ice-free region in Antarctica, supports microbially-dominated ecosystems that experience extremes of temperature, salinity, nutrient availability, and solar radiation. A changing Antarctic climate leads to alteration of these natural gradients, thus, studying how organisms respond to changing stressors can inform predictions of future impacts to ecosystems. This dissertation elucidates how MDV microorganisms interact with their environment through culture-based and multi-omics techniques performed on both environmental materials and bacterial isolates. We describe the ecophysiology of a red pigmented strain of Massilia frigida (strain DJPM01) isolated from a microbial mat. Through genomic analyses, adaptations to cold and saline environments, and biosynthesis genes for the pigment prodigiosin were identified. The synthesis of prodigiosin was confirmed using mass spectrometry, and breakdown of this pigment was observed when DJPM01 cultures were incubated under ultraviolet light, a relevant stressor for polar bacteria. To investigate the impact of salinity on whole communities and individual species, we leveraged samples from a natural salinity gradient in MDV soils that forms from permafrost melt. Environmental soil DNA was sequenced to examine differences in community structure and potential correlations with salinity. We then identified changes in transcription and metabolite production in a potentially novel Gillisia sp., isolated from this soil gradient, under elevated salt concentrations. A Shewanella sp. BF02_Schw, isolated from a Mars analog feature known as Blood Falls, was used to describe biosignatures produced during iron reduction, a plausible metabolic strategy for life on early Earth and Mars. Employing instrumentation relevant to both in situ and sample return Mars missions, we identified mineral and molecular biosignatures produced under high iron concentration and confirmed the biogenicity of these signatures via transcriptomics. Collectively, this dissertation describes specific ways that MDV microorganisms interact with their environment that provide insight into the impact of climatic change on Antarctic communities and inform strategies for the detection of life on other planets.

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