Ethylene is one of the world’s most important industrial chemicals. It is used to manufacture polyethylene plastics, solvents, antifreeze, coatings and numerous other products. Conventional ethylene production depends mainly on fossil-based petrochemical processes that require high temperatures and significant energy input. Photosynthetic microorganisms offer a fundamentally different approach. Using light as an energy source, they can convert carbon dioxide into carbon-containing molecules under relatively mild conditions. However, turning this biological capability into a practical production technology has proven difficult.

Most photosynthetic production systems use cells suspended in large tanks of liquid. These cultures must be mixed continuously so that the cells remain evenly distributed and have access to light, nutrients and carbon dioxide. The arrangement creates several bottlenecks. Large quantities of water are needed, mixing consumes energy, and dense populations of cells shade one another. Cells close to the light source absorb much of the incoming radiation, leaving cells deeper in the culture with less energy for photosynthesis. As the system becomes larger, this self-shading effect can limit productivity and complicate reactor design.

The University of Turku team, working with researchers at VTT Technical Research Centre of Finland, tackled these problems by embedding ethylene-producing cyanobacteria in thin films made from nanocellulose. Nanocellulose consists of extremely small cellulose fibrils that can form lightweight, porous and water-retaining structures. In the new material, the scaffold provides physical support for the microorganisms while allowing light, carbon dioxide and moisture to reach the cells. Rather than growing freely through a tank, the cyanobacteria remain immobilised inside a thin, hydrated matrix that functions as a living biocatalyst.

The researchers tested the films in a continuous-flow biofilm reactor. The material was kept moist while the cell-containing surface was exposed to the reactor headspace, creating conditions that allowed the volatile ethylene produced by the cyanobacteria to escape from the film and be collected. This design separates the biological production zone from the liquid environment used by conventional suspension cultures. It also reduces the need to keep large quantities of cells mixed in water, while maintaining the hydration required for photosynthesis and cellular metabolism.

The most striking result was the durability of the system. The cyanobacterial films continued producing ethylene for more than four months, a period substantially longer than the short production windows commonly reported in laboratory studies of photosynthetic biomanufacturing. Over the operating period, the films generated up to roughly twice the amount of ethylene produced by comparable suspension cultures. The result suggests that immobilising the cells can improve not only operational stability but also the effective use of light and carbon within the production system.

The researchers believe the structure of the films is important to this performance. In a freely growing culture, cells divide and accumulate biomass, eventually increasing turbidity and intensifying self-shading. Within the nanocellulose matrix, cell division and excessive biomass accumulation are restricted. This may redirect a larger share of the captured carbon and metabolic energy toward ethylene formation rather than toward producing more cellular material. The matrix also helps maintain a favourable local environment by retaining water and giving the cells a stable physical location, potentially reducing some of the stresses associated with prolonged cultivation.

The study forms part of a broader effort to design photosynthetic microorganisms as long-lived industrial catalysts rather than simply as growing cultures. In related work, the Turku researchers have explored how cells with different light-harvesting properties can be arranged in layers. Cells with smaller antenna structures can be positioned closer to the incoming light, while cells with larger antennae are placed deeper in the material. Because antenna proteins determine how efficiently cells capture and distribute light energy, this arrangement can spread illumination more evenly through the biocatalyst and improve the conversion of light into chemical products.

The nanocellulose films also showed a potentially important environmental advantage: after the production phase, the formulations could be biodegraded. This feature could make it easier to develop disposable, recyclable or circular production materials, although the environmental performance of a future industrial system would depend on the full life cycle of the films, nutrients, reactor equipment and product-recovery processes. The researchers emphasise that the technology remains at the laboratory stage. Larger films and reactors will need to maintain uniform light exposure, hydration, carbon dioxide delivery and ethylene recovery while achieving higher production rates.

Scaling will be especially challenging because light behaves differently in large biological systems than in small laboratory devices. Thick or densely packed films may recreate the same shading problems found in suspension cultures, while insufficient moisture could reduce cellular activity. Reactor architecture, film geometry and gas flow will therefore need to be developed alongside the biology. The team’s next objective is to integrate engineered cells, nanocellulose materials and reactor systems into reliable larger-scale platforms. If those challenges can be overcome, solid-state photosynthetic cell factories could become a new class of solar-driven manufacturing technology, producing renewable chemicals with less water, lower mixing requirements and a potentially smaller energy footprint than conventional cultivation systems.

Subject of Research: Solid-state photosynthetic cell factories using engineered cyanobacteria immobilised in nanocellulose films for long-term ethylene production.

Article Title: Over 4 months of ethylene production using solid-state photosynthetic cell factories

News Publication Date: 2-Jul-2026

Web References: https://doi.org/10.1016/j.tibtech.2026.06.006

References: Trends in Biotechnology; DOI: 10.1016/j.tibtech.2026.06.006

Keywords

Cyanobacteria, ethylene production, nanocellulose, photosynthetic biomanufacturing, biohybrid materials, renewable chemicals, carbon dioxide conversion, solid-state biocatalysts, sustainable fuels, synthetic biology

At the crux of this investigation lies the enzyme MAR, which certain bacteria use to convert organic sulfur compounds into ethylene. For the first time, scientists have successfully extracted MAR in its pure enzymatic form, an unprecedented accomplishment that has opened the door to an enhanced understanding of its function and structure. This feat, led by Justin North and his team at Ohio State along with their colleagues at UCLA and DOE laboratories, sets the stage for bioengineered applications wherein such enzymes could replace fossil-fuel-based ethylene synthesis methods.

The investigative journey began with genetic explorations that revealed curious homology between the genes encoding MAR and those responsible for nitrogenase enzymes, which fix atmospheric nitrogen into biologically usable forms. This unexpected link suggested a deep evolutionary connection and hinted at the presence of complex metal cofactors integral to the enzyme’s catalytic activity. Nitrogenases, characterized by intricate iron-sulfur clusters, have long been regarded as among the most sophisticated metalloenzymes known in nature.

Capitalizing on advanced synthetic biology, researchers employed gene synthesis technologies to produce multiple MAR genetic variants, subsequently expressing these genes within the soil bacterium Rhodospirillum rubrum. This enabled the production and isolation of MAR protein in quantities sufficient for detailed study. Srividya Murali’s pioneering efforts in protein isolation were instrumental in overcoming prior technical barriers, rendering the enzyme amenable to biophysical and structural elucidation.

Spectroscopic analyses, spearheaded by Hannah Shafaat’s group at UCLA, illuminated the intricate electron transfer processes governing MAR’s catalytic conversion of sulfur compounds into ethylene. These measurements revealed that MAR’s metal cofactors engage in complex redox activities, reflecting both parallels and distinctions from nitrogenase. The electron flow pathways sculpted within MAR’s massive protein complex underscore its finely tuned catalytic prowess, manifested in selective sulfur extraction and ethylene generation.

Structural revelations afforded by cryogenic electron microscopy at Brookhaven National Laboratory further demystified MAR’s molecular composition. Researchers unveiled that MAR shares notable architectural motifs with nitrogenase, though its metal center exhibits distinctive variations tailored to its unique chemical function. These metal cofactors comprise clusters of iron and sulfur atoms assembled in configurations that enable remarkable catalytic versatility. Such structural nuances explain MAR’s predilection for sulfur extraction compared to nitrogenase’s nitrogen-fixing role.

The elucidation of MAR’s structure-function relationship fosters a nuanced understanding of how evolutionary cousins among enzymes adapt metal centers to perform distinct catalytic tasks. This insight not only enriches the fundamental biochemistry of metalloenzymes but also provides a tangible framework for future enzyme engineering endeavors. The ultimate ambition is to optimize MAR variants with superior ethylene production efficiency under industrially relevant conditions, thereby enabling a transition to bio-based ethylene synthesis.

Transitioning from fundamental science to applied biotechnology, the researchers aspire to harness MAR as a biocatalyst that can supplant traditional ethylene production processes. Achieving this requires strategic protein engineering to enhance turnover rates, stability, and substrate specificity, thus ensuring that microbial ethylene generation is both economically and environmentally competitive. This pursuit aligns with broader objectives of reducing greenhouse gas emissions and reliance on non-renewable resources in chemical manufacturing.

Collaboration among interdisciplinary teams—integrating microbiology, biochemistry, synthetic biology, spectroscopy, and structural biology—has been pivotal in this scientific advance. The fusion of expertise from Ohio State University, UCLA, and DOE facilities exemplifies how cooperative research accelerates breakthroughs that hold promise for sustainable industrial innovations. Such partnerships also highlight the pivotal role of cutting-edge instrumentation and methodologies, from genetic engineering platforms to high-resolution cryo-EM.

The research makes significant headway by not only uncovering the evolutionary lineage of MAR but also elucidating how its metal cofactors orchestrate electron movement during catalysis. Understanding these molecular intricacies affords strategic entry points for modifying the enzyme’s active sites or electron pathways to boost efficiency. This work thereby paves a path for rational design approaches aimed at tailoring enzymes for bespoke chemical transformations.

As environmental imperatives intensify the need for alternative materials chemistry, this pioneering study marks an important milestone in the convergence of microbiology and green chemistry. It lays the foundation for a future where bioengineered microbes equipped with optimized MAR enzymes could serve as renewable ethylene factories, reducing plastic production’s carbon footprint. The promise of a fossil fuel–independent ethylene synthesis system is tantalizingly close, enabled by a profound comprehension of bacterial enzyme sophistication.

This study was financed by the Department of Energy’s Office of Science under its Physical Biosciences program, reflecting governmental commitment to fostering scientific research addressing sustainability challenges. The multi-institutional collaboration, technical innovations, and fundamental discoveries position this research on the cutting edge, offering both immediate scientific impact and long-term industrial relevance.

In summary, the identification, isolation, and comprehensive characterization of methylthio-alkane reductase have illuminated a biochemical pathway for sustainable ethylene synthesis via bacterial metabolism. At the intersection of microbiology, enzymology, and materials science, this achievement signals a paradigm shift in how we might reimagine plastic production—transforming an ancient bacterial enzyme into a cornerstone of the circular bioeconomy.

Subject of Research: Not applicable

Article Title: Architecture, catalysis and regulation of methylthio-alkane reductase for bacterial sulfur acquisition from volatile organic compounds

News Publication Date: 23-Oct-2025

Web References:

• Nature Catalysis Article
• North Lab at Ohio State
• Shafaat Lab at UCLA
• DOE Joint Genome Institute
• Brookhaven National Lab Cryo-EM

References:

• North, J., et al. (2025). Architecture, catalysis and regulation of methylthio-alkane reductase for bacterial sulfur acquisition from volatile organic compounds. Nature Catalysis. DOI: 10.1038/s41929-025-01425-3
• North, J., et al. (2020). A new method for making a key component of plastics. Science. DOI: 10.1126/science.abb6310

Image Credits: Not provided

Keywords

Methylthio-alkane reductase, ethylene biosynthesis, bacterial enzymes, nitrogenase analogs, metalloenzyme structure, iron-sulfur clusters, cryogenic electron microscopy, enzyme engineering, sustainable plastics, bio-based ethylene, enzymatic catalysis, microbial biotechnology