KAIST announced that a research team led by Professor Jaewook Myung from the Department of Civil and Environmental Engineering, in collaboration with Stanford University, has identified how ethane (C2H6)—a major constituent of natural gas—affects the core metabolic pathways of the obligate methanotroph Methylosinus trichosporium OB3b.
Methane (CH4), a greenhouse gas with roughly 25 times the global warming potential of carbon dioxide, is rarely emitted alone into the environment. It is typically released in mixtures with other gases. In the case of natural gas, ethane can comprise up to 15% of the total composition.
Methanotrophs are aerobic bacteria that can utilize methane as their sole source of carbon and energy. Obligate methanotrophs, in particular, strictly utilize only C1 compounds such as methane or methanol. Until now, little was known about how these organisms respond to C2 compounds like ethane, which they cannot use for growth.
This study reveals that although ethane cannot serve as a growth substrate, its presence significantly affects key metabolic functions in M. trichosporium OB3b—including methane oxidation, cell proliferation, and the intracellular synthesis of polyhydroxybutyrate (PHB), a biodegradable polymer.
Under varying methane and oxygen conditions, the team observed that ethane addition consistently resulted in three metabolic effects: reduced cell growth, lower methane consumption, and increased PHB accumulation. These effects intensified with rising ethane concentrations. Notably, ethane oxidation occurred only when methane was present, confirming that it is co-oxidized via particulate methane monooxygenase (pMMO), the key enzyme responsible for methane oxidation.
Further analysis showed that acetate, an intermediate formed during ethane oxidation, played a pivotal role in this response. Higher acetate levels inhibited growth but enhanced PHB production, suggesting that ethane-derived acetate drives contrasting carbon assimilation patterns depending on nutrient conditions—nutrient-balanced growth phase and nutrient-imbalanced PHB accumulation phas.
In addition, when external reducing power was supplemented (via methanol or formate), ethane consumption was enhanced significantly, while methane oxidation remained largely unaffected. This finding suggests that ethane, despite not supporting growth, actively competes for intracellular resources such as reducing equivalents. It offers new insights into substrate prioritization and resource allocation in methanotrophs under mixed-substrate conditions.
Interestingly, while methane uptake declined in the presence of ethane, the expression of pmoA, the gene encoding pMMO, remained unchanged. This suggests that ethane's impact occurs beyond the transcriptional level—likely via post-transcriptional or enzymatic regulation.
"This is the first study to systematically investigate how obligate methanotrophs respond to complex gas mixtures involving ethane," said Professor Jaewook Myung. "Our findings show that even non-growth substrates can meaningfully influence microbial metabolism and biopolymer synthesis, opening new possibilities for methane-based biotechnologies and bioplastic production."
The study was supported by the National Research Foundation of Korea, the Ministry of Land, Infrastructure and Transport, and the Ministry of Oceans and Fisheries. The results were published in Applied and Environmental Microbiology, a journal of the American Society for Microbiology.
