Biological Sciences, School of


First Advisor

Nicole R. Buan

Date of this Version



Carr, S. R. 2022. Methanogen Metabolic Flexibility. University of Nebraska - Lincoln.


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Biological Sciences (Genetics, Cellular, and Molecular Biology), Under the Supervision of Professor Nicole R. Buan. Lincoln, Nebraska: July, 2022

Copyright © 2022 Sean R. Carr


Methanogens are obligately anaerobic archaea which produce methane as a byproduct of their respiration. They are found across a wide diversity of environments and play an important role in cycling carbon in anaerobic spaces and the removal of harmful fermentation byproducts which would otherwise inhibit other organisms. Methanogens subsist on low-energy substrates which requires them to utilize a highly efficient central metabolism which greatly favors respiratory byproducts over biomass. This metabolic strategy creates high substrate:product conversion ratios which is industrially relevant for the production of biomethane, but may also allow for the production of value-added commodities. Particularly of interest are terpene compounds, as methanogen membranes are composed of isoprenoid lipids resulting in a higher flux through isoprenoid biosynthetic pathways compared to Eukarya and Bacteria. To assess the metabolic plasticity of methanogens, our laboratory has engineered the methanogen Methanosarcina acetivorans to produce the hemiterpene isoprene. We hypothesized that isoprene producing strains would result in a decreased growth phenotype corresponding to a depletion of metabolic precursors needed for isoprenoid membrane production. We found that the engineered methanogens responded well to the modification, directing up to 4% of total towards isoprene production and increasing overall biomass despite the additional metabolic burden. Using flux balance analysis and RNA sequencing we investigated how the engineered strains respond to isoprene production and how production can be enhanced.

Advisor: Nicole R. Buan