Scientists Discover Ethane's Surprising Influence on Methane-Eating Bacteria for Environmental Solutions

A groundbreaking collaborative study by Professor Jae-Wook Myung's research team from KAIST's Department of Civil and Environmental Engineering, in partnership with Stanford University, has revealed a novel pathway to combat both potent greenhouse gas emissions and plastic pollution. Published on the July 10 edition of Applied and Environmental Microbiology, the research focused on the often-overlooked interaction between methane (CH₄) and ethane (C₂H₆), two prevalent gases in natural gas and various emission sources like landfills, livestock operations, and wastewater treatment plants. Methane, a potent greenhouse gas, is approximately 25 times more effective at trapping heat than carbon dioxide (CO₂) over a 100-year period, making its reduction an urgent global priority for climate action. Ethane, while less discussed in climate contexts, can constitute up to 15% of natural gas after methane.

The study centered on Methylosinus trichosporium OB3b, a type of "obligate methanotroph" – bacteria that are uniquely adapted to consume methane as their sole source of energy in the presence of oxygen. While these bacteria are known for their role in natural methane reduction, the impact of co-existing ethane on their metabolism was previously unknown.

The research team conducted experiments by introducing ethane alongside methane to cultures of Methylosinus trichosporium OB3b under controlled conditions. The results were remarkable and consistently demonstrated three key metabolic shifts:

1. Inhibited Cell Growth: The presence of ethane led to a reduction in the overall growth of the bacterial cells.
2. Decreased Methane Consumption: Unexpectedly, the bacteria consumed less methane when ethane was also present.
3. Boosted Bioplastic Production: Most significantly, the bacteria dramatically increased their synthesis of Polyhydroxybutyrate (PHB), a natural, fully biodegradable polymer that is a promising raw material for bioplastics. These effects became more pronounced as the concentration of ethane increased in the gas mixture.

The scientists delved deeper to understand this intriguing phenomenon. They discovered that while ethane is not used by these bacteria for growth, their primary methane-oxidizing enzyme, "particulate methane monooxygenase (pMMO)," inadvertently "co-oxidizes" ethane when methane is available. This process generates an intermediate compound called acetate. The research pinpointed acetate as the key regulator: it acts as a signal within the bacterial cells, inhibiting growth but simultaneously triggering a massive increase in PHB (Polyhydroxybutyrate) production. This suggests that under certain metabolic stresses, such as those induced by acetate, the bacteria prioritize energy storage in the form of PHB.

Meanwhile , although methane consumption decreased when ethane was added , there was no significant change in the expression level of the pmoA gene , which constitutes the methanogenic enzyme pMMO . This demonstrates that ethane does not affect the transcription level of the gene, but instead affects the actual working ability ( activity level ) of the enzyme or the post-transcriptional regulation step . 

The research team analyzed that ethane acts as a regulator that indirectly controls the metabolic flow of methanotrophs , and when present with methane, it affects cell growth and PHB production in an unintended way .

"This study marks the first systematic elucidation of how obligate methanotrophs metabolically respond under complex substrate conditions like those found with ethane, moving beyond the traditional single-substrate environment," explained Professor Jae-Wook Myung. "By clarifying the effect of non-growth substrates such as ethane on methane metabolism and biodegradable polymer production, our findings suggest novel avenues for both biological methane reduction technologies and the sustainable production of bioplastics."

The ability to enhance bioplastic production from a potent greenhouse gas, coupled with methane reduction, presents a promising avenue for sustainable industry and a healthier planet and holds immense potential for developing innovative solutions to global environmental challenges. 

The research, with doctoral student Seonho Park as the first author, was supported by the National Research Foundation of Korea, the Ministry of Land, Infrastructure and Transport, and the Ministry of Oceans and Fisheries.