Date of Award
2025
Document Type
Open Access Dissertation
Degree Name
Doctor of Philosophy in Biochemistry and Molecular Biology (PhD)
Administrative Home Department
Department of Biological Sciences
Advisor 1
Stephen Techtmann
Committee Member 1
Tarun Dam
Committee Member 2
Trista Vick-Majors
Committee Member 3
Rupali Datta
Abstract
Microbes are essential in keeping our environment balanced, especially by fixing carbon dioxide and breaking down hydrocarbons in aquatic sediments. This thesis explores how microbial communities perform these tasks in different sediment environments, including marine areas (Caspian Sea and Mediterranean Sea) and freshwater ecosystems (Great Lakes). The first part of this thesis reviews current knowledge about how microbes degrade hydrocarbons. It highlights the importance of different pathways microbes use depending on oxygen availability. The second part provides a detailed study of the microbial communities found in marine sediments from the Caspian Sea and Mediterranean Sea, showing that microbes in these deeper, oxygen-limited sediments mainly use anaerobic (oxygen-free) pathways for degrading hydrocarbons.
In the third part, another review focuses on hydrocarbon degradation mechanisms in freshwater (Great Lakes). The fourth part investigates microbial carbon fixation, the process microbes use to convert carbon dioxide into organic matter in sediments from marine and freshwater environments. The results reveal that marine microbes, especially in deeper sediments, predominantly rely on anaerobic carbon fixation pathways like the Wood–Ljungdahl pathway and reverse TCA cycle. In contrast, freshwater sediments from the Great Lakes show greater diversity, with microbes using aerobic (oxygen-requiring) pathways such as glycine and hydroxypropionate cycles due to higher oxygen availability. An important discovery of this thesis is the metabolic flexibility of certain microbes, known as facultative autotrophy. Based on environmental conditions, these microbes can switch between using inorganic carbon (carbon dioxide) and organic carbon (such as hydrocarbons). This ability helps them survive and adapt to changing sediment environments. Additionally, this research found that carbon fixation pathways are present in various microbes, including many previously not recognized for this ability, emphasizing their importance across microbial life.
Overall, this work significantly improves our understanding of how sediment microbes adapt their metabolic strategies according to environmental conditions like oxygen levels and sediment depth. These insights help us predict how microbial communities respond to environmental changes, making this knowledge valuable for future environmental management, carbon sequestration strategies, and pollution cleanup efforts.
Recommended Citation
Warkhade, Yogita M., "MICROBIAL HYDROCARBON DEGRADATION AND CARBON CYCLING IN MARINE AND FRESHWATER SEDIMENTS: A COMPARATIVE METAGENOMIC ANALYSIS", Open Access Dissertation, Michigan Technological University, 2025.