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Title of the thesis: Unlocking the hidden metabolic potential of Methanosarcina acetivorans.

Thesis defender: Tejas Somvanshi
Opponent: Prof. Cornelia Welte, Radbound University, Netherlands
Custos: Associate prof. Silvan Scheller, Aalto University School of Chemical Engineering
 

The study examined the metabolic potential and electron-transfer biology of Methanosarcina acetivorans. It focused on how this methanogen can use ethanol, formate, hydrogen, and serine as electron donors. The purpose was to understand and broaden M. acetivorans’ substrate and electron-donor scope, resolve open questions about hydrogen and ethanol use, and engineer strains and tools for biotechnology and mechanistic studies. This work is highly relevant because M. acetivorans is a key model for cytochrome-containing methanogens. It advances knowledge of methanogenesis and electron transfer, informs biogenic ethane origins, reassesses formate metabolism in Methanosarcinales, and guides archaeal genome engineering. What results were obtained? Cas12a editing revealed intrachromosomal translocations despite the absence of canonical NHEJ. The promiscuous methylotrophic pathway reduced ethanol to ethane. Heterologous expression of an F420-reducing formate dehydrogenase enabled formate-dependent methanogenesis. Engineered strains channeled electrons from formate via the native H2-independent chain to reduce ferredoxin and in the JB-MF chassis, hydrogen and serine served as electron donors for methyl-reducing methanogenesis, all of which highlighted the substantial plasticity in electron-transfer networks. The findings can be applied to engineer methanogens to use low-cost donors (formate, H2, serine) for methane or alkane production. The JB-MF chassis enables testing and evolution of oxidoreductases. Ecologically, the work informs interpretation of trace ethane and reassesses formate’s role in Methanosarcinales. In synthetic biology, it guides safer CRISPR designs in archaea. M. acetivorans is more metabolically flexible than previously recognized and can be engineered to expand its electron-donor range. Electron transfer can be rewired to support methyl reduction without obligatory H2. Cas12a-based editing may cause chromosomal rearrangements, necessitating careful validation. These insights open avenues for bioenergy and mechanistic studies.
 

Methanosarcina acetivorans, formate dehydrogenase, metabolic engineering, methane, ethane, substrate promiscuity, hydrogen, serine, alternate electron donors 

Thesis available for public display 7 days prior to the defence at .

Contact information: tej.somvanshi@gmail.com