| dc.description.abstract | This work describes an in-depth investigation into how the methane-oxidizing bacteria (MOB) respond to changes that allow them to effectively function in their ecological role. This includes understanding their response to unfavorable oxygen concentrations, and how they respond in co-culture with other bacteria. This work also presents the characterization of a novel species of MOB; Methylocystis suflitae sp. nov. MOB play a crucial role in the global methane cycle, serving as significant actors in biogeochemical cycling. However, their physiological response to changing oxygen concentrations remains incompletely understood. One of the studies presented in this dissertation investigates how two MOB species, Methylosinus trichosporium OB3b and Methylomonas sp. WSC-7, respond to changing oxygen concentrations and the addition of catalase, a hydrogen peroxide scavenger, in growth media. Through transcriptomics analysis, this work showed that under high oxygen conditions, M. trichosporium OB3b upregulates genes involved in reactive oxygen species (ROS) defense, including cytochrome c peroxidase and superoxide dismutase, suggesting a need to deal with elevated ROS levels. Conversely, Methylomonas sp. WSC-7 exhibits cell clustering behavior, potentially as a defense mechanism against ROS toxicity. Differential expression of flagellar biosynthesis genes and chemotaxis response genes further supports this adaptive response. Moreover, Methylomonas sp. WSC-7 shows reduced expression of soluble methane monooxygenase genes under low oxygen conditions, while M. trichosporium OB3b exhibits higher expression under catalase-amended conditions, and that rates of methane oxidation for both strains are impacted by the concentration of oxygen and amending the growth media with catalase. Our findings underscore the importance of oxygen concentration in modulating MOB physiology and suggest potential strategies for optimizing their growth conditions. Additionally, despite the MOB’s crucial role in biogeochemical cycling, there is still a lot to learn about how the MOB interact with other bacteria in their environment. Another aspect of this study investigates the growth conditions and community dynamics of methane-oxidizing co-cultures, focusing on the interactions between M. trichosporium OB3b (MOB) and the non-methane-oxidizing heterotrophic bacteria (NMOHB) of the genera Flavobacterium, Cupriavidus, and Pseudomonas. Heterotrophic plate counts were used to determine whether NMOHB could grow in methane-oxidizing co-cultures. There was growth of all three NMOHB, suggesting carbon substrate utilization derived from methane oxidation. Furthermore, co-cultures with Pseudomonas chlororaphis HC exhibited enhanced methane oxidation rates compared to monoculture, indicating a stimulating effect of P. chlororaphis HC on methane utilization by MOB. Transcriptomic analysis revealed differential gene expression patterns in both MOB and NMOHB during co-culture and points to potential cross-feeding of C4 dicarboxylates and methanol from the MOB to the NMOHB. Further, NMOHB displayed upregulation of genes involved in ROS remediation, suggesting a response to oxidative stress induced by methane oxidation. Additionally, NMOHB exhibited alterations in nitrogen utilization and amino acid metabolism genes, possibly reflecting adaptations to the co-culture environment. Overall, these findings shed light on the metabolic interactions between MOB and NMOHB in methane-oxidizing systems, highlighting the potential for carbon sharing, nitrogen exchange, and ROS defense mechanisms. | en_US |
