Date of Award
1-1-2025
Document Type
Dissertation
Degree Name
Ph.D. in Biological Science
First Advisor
Patrick Curtis
Second Advisor
Cole Stevens
Third Advisor
Erick Hom
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
Bacteria are ubiquitous and capable of colonizing nearly any environment, including extreme conditions such as deep oceans, high altitudes, and even space-faring vehicles. These vehicles present unique stresses not found on Earth such as microgravity and radiation. As space exploration advances, understanding how microgravity affects bacterial life has become increasingly important. Over the past 60 years, studies using both real and simulated microgravity have revealed species-specific responses, collectively indicating broad changes in bacterial function and physiological adaptations.
Initially, this study examined Novosphingobium aromaticivorans, a lignin-degrading bacterium detected in spacecraft cleanroom environments by assessing gene fitness during growth in microgravity on a whole genome scale using high density transposon mutagenesis. We developed TnDivA, a comparative TnSeq tool that leverages biological replicates to evaluate differences between two conditions, here microgravity and normal gravity, using a modified Shannon diversity index. Various statistical methods, including log2-fold change, regression analysis, and Welch’s t-test, were applied to compare effective density between conditions. These methods identified genes with high fitness during spaceflight were primarily involved in core functions such as lipid metabolism, energy production, transcription, translation, and notably, secondary metabolism.
With these foundations, the final chapter examined the production of plant-beneficial compounds under simulated microgravity. P. protegens and B. ambifaria, known producers of secondary metabolites such as pyoluteorin, 2,4-DAPG, orfamide A , and PQQ, key agents in biocontrol and plant health, showed altered regulation under simulated microgravity. Both transcriptomic and metabolomic analyses revealed changes in the expression and production of these compounds. Notably, orfamide A in P. protegens and PQQ in B.ambifaria, a well-characterized antifungal compounds, exhibited significant downregulation at the transcriptional level and reduced accumulation in metabolite profiles, indicating coordinated suppression under microgravity conditions.
To boost metabolic production under microgravity, genetic engineering strategies were employed. While promoter replacements led to modest improvements in orfamide A production in P. protegens, plasmid-based overexpression significantly enhanced pyrroloquinoline production in B. ambifaria. These studies reveal how microgravity impacts bacterial fitness and function, while highlighting the potential of engineered bacteria as essential partners in future space agriculture and life support systems.
Recommended Citation
Sharma, Gayatri, "Microgravity-Induced Effects on Global Gene Fitness and Secondary Metabolite Yield in Bacteria" (2025). Electronic Theses and Dissertations. 3386.
https://egrove.olemiss.edu/etd/3386