How a Microbial Enzyme Could Transform Sustainable Plastic Manufacturing

In a new study , Dr. Johannes G. Rebelein and his team at the Max Planck Institute for Terrestrial Microbiology in Marburg, Germany, have uncovered the detailed structure of a bacterial enzyme that could one day help produce renewable plastics. The enzyme, called methylthio-alkane reductase, or MAR, was isolated from the bacterium Rhodospirillum rubrum. It enables the microorganism to generate ethylene; a crucial building block for plastics; under oxygen-free conditions, without releasing carbon dioxide. This finding provides a foundation for a new, potentially low-carbon pathway for chemical manufacturing.

Lago-Maciel, A., Soares, J. C., Zarzycki, J., Buchanan, C. J., Reif-Trauttmansdorff, T., Schmidt, F. v., Lometto, S., Paczia, N., Schuller, J. M., Hansen, D. F., Heller, G. T., Prinz, S., Hochberg, G. K. A., Pierik, A. J., & Rebelein, J. G. (2025). Methylthio-alkane reductases use nitrogenase metalloclusters for carbon–sulfur bond cleavage. Nature Catalysis, 8(10), 1086–1099. https://doi.org/10.1038/s41929-025-01426-2

The global demand for ethylene is immense. It serves as a feedstock for many products, including polyethylene, one of the world’s most widely used plastics. At present, almost all ethylene is made from fossil fuels through energy-intensive cracking processes that emit significant amounts of CO₂. Biologists and chemical engineers have long sought a renewable method of producing ethylene that avoids these emissions. However, few natural enzymes are known to form ethylene, and those that do often require costly substrates and still generate CO₂ as a by-product.

Dr. Johannes G. Rebelein from Max Planck Society stated,

“In fact, the enzyme has remarkable versatility. It can sustainably produce a range of hydrocarbons including ethylene, ethane and methane.”

The discovery of methylthio-alkane reductase in Rhodospirillum rubrum changed this perspective. The enzyme catalyzes reactions involving volatile organic sulfur compounds under anaerobic conditions, resulting in small hydrocarbons such as ethylene, ethane, and methane. Because it functions without oxygen and does not release carbon dioxide, MAR immediately drew attention as a biological model for sustainable ethylene production.

For several years, research on MAR was limited by the enzyme’s extreme sensitivity to oxygen. Its active components; large iron-sulfur clusters; are easily damaged in the presence of air, making the enzyme difficult to purify and analyze. Until recently, MAR could only be observed within bacterial cells, which prevented researchers from understanding how it performed its reactions.

Dr. Rebelein’s team, working with collaborators from RPTU Kaiserslautern, succeeded in purifying MAR under strictly anaerobic conditions. Using advanced spectroscopic and structural methods, including cryo-electron microscopy at near-atomic resolution, the researchers were able to visualize the enzyme’s internal architecture for the first time.

Their analysis revealed that MAR contains large and complex iron-sulfur clusters previously thought to exist only in nitrogenases. Nitrogenases are ancient enzymes responsible for converting atmospheric nitrogen into ammonia, making it available to living organisms. These clusters; arrangements of iron, sulfur, and sometimes carbon atoms; are among the most intricate known in biology and are considered one of life’s earliest chemical tools.

In MAR, the researchers found that these same cluster types perform an entirely different function. Rather than breaking nitrogen bonds, they enable the cleavage of carbon-sulfur bonds, resulting in the release of hydrocarbons such as ethylene. This marks the first time such nitrogenase-type clusters have been observed in a non-nitrogenase enzyme.

Doctoral researcher Ana Lago-Maciel, the study’s first author, explained that this finding reshapes our understanding of how metal clusters can evolve and adapt to different biochemical tasks. It also raises new questions about the early evolution of these complex catalytic systems. The team suggests that similar cluster-based enzymes may have existed before nitrogenases evolved, hinting at a broader and more ancient role for these metal assemblies in shaping the chemistry of early Earth.

The potential of MAR extends beyond evolutionary biology. From an engineering perspective, the enzyme offers a possible template for designing new biocatalysts capable of producing hydrocarbons sustainably. Because MAR works without oxygen and avoids carbon dioxide release, it represents a chemical route that could reduce emissions in the production of plastic precursors.

Dr. Rebelein notes that MAR is unusually versatile for an enzyme of its kind. It can generate a range of hydrocarbons, not just ethylene, and its activity can vary depending on the substrate available. This adaptability could be valuable for future bioengineering efforts aiming to produce different chemical feedstocks.

The enzyme’s structure also provides valuable insight into how the protein scaffold surrounding the metal clusters controls their reactivity. By adjusting specific amino acids or structural elements, scientists may one day fine-tune MAR to produce desired hydrocarbons more efficiently or selectively. According to Dr. Rebelein, understanding these relationships is a key step toward using MAR in industrial biotechnology.

Despite its promise, many challenges remain before MAR can be used on an industrial scale. Its oxygen sensitivity means that any future production system would have to operate under strictly anaerobic or low-oxygen conditions, which can be costly to maintain. Additionally, the enzyme’s natural substrates; volatile sulfur compounds; are not yet produced in large quantities, and the enzyme’s turnover rate is still relatively low compared with that of industrial catalysts.

Process engineers would also need to design reactors capable of safely collecting gaseous products such as ethylene and methane while maintaining the delicate biochemical environment required for MAR activity. Moreover, the enzyme’s stability and longevity under manufacturing conditions would need significant improvement to make large-scale use viable.

Still, the research community views this as a major step forward. By revealing the enzyme’s detailed structure and mechanism, the study provides the foundation for future protein engineering efforts. If MAR or its engineered variants can be optimized for robustness and higher activity, they could form part of a biological process that generates renewable hydrocarbons directly from waste materials or other sustainable feedstocks.

The discovery of nitrogenase-like clusters in MAR also carries broader scientific implications. It challenges the traditional idea that these clusters are unique to nitrogen fixation and suggests they may play roles in other types of biochemical transformations. This insight could inspire searches for similar enzymes in other microorganisms and possibly uncover additional natural systems capable of catalyzing useful chemical reactions.

For engineers and synthetic biologists, MAR represents an example of nature’s efficiency in reusing molecular designs. It demonstrates how ancient catalytic machinery can be repurposed for new chemical functions—an approach that could guide the creation of next-generation biotechnological tools.

The work by Dr. Rebelein and his team is not only a scientific breakthrough but also a conceptual one. It shows that biological systems can offer blueprints for industrial processes that are both efficient and sustainable. By bridging microbiology, biochemistry, and process engineering, the study opens a pathway toward a future where plastics and other essential materials might be produced from renewable biological sources rather than fossil fuels.

As Dr. Rebelein puts it, the ultimate goal is to understand these enzymes well enough to “tame them” biotechnologically; to control their reactivity and tailor their output to human needs. Although practical applications are still distant, this work moves one step closer to achieving that vision.

The study, “Methylthio-alkane reductases use nitrogenase metalloclusters for carbon; sulfur bond cleavage,” by Ana Lago-Maciel, Johannes G. Rebelein. The findings mark a significant advancement in understanding how microbial enzymes could one day contribute to sustainable chemical production, blending the ancient chemistry of life with the modern challenge of renewable manufacturing.