Researchers at the University of Turku in Finland have developed a thin-layer artificial biofilm technology for sustainable and long-term ethylene photoproduction. In the process, described in an open-access paper in the RSC journal Green Chemistry, recombinant Synechocystis sp. PCC 6803 cells holding ethylene forming enzyme (Efe) from Pseudomonas syringae are entrapped within a natural polymer matrix, thus forming the thin-layer biocatalytic structure.
The team optimized the production system by varying different parameters, such as radiance, inorganic carbon level, and periodicity of medium renewal. As a result, artificial films with entrapped cells of Synechocystis sp. PCC 6803 mutant produced ethylene for up to 38 days, yielding 822 mL m−2 ethylene at 1.54% light to ethylene conversion efficiency.
These figures represent a 2-time enhancement in the duration of ethylene production; a 2.2-fold increase in the production yield; and a 3.5-fold improvement in the light to ethylene conversion efficiency as compared to the cell suspension.
This study demonstrates that ethylene producing cyanobacteria entrapped in the polymeric matrix could truly act as photo-biocatalyst for the prolonged ethylene production by strongly limiting biomass accumulation and maintaining photosynthetic activity and cell fitness.—Vajravel et al.
Ethylene (earlier post) is one of the most important organic commodity chemicals with an annual global demand of more than 150 million tons. It is the main building block in the production of plastics, fibers and other organic materials.
Ethylene has a high energy density that also makes it an attractive fuel source. Currently, ethylene is produced via steam cracking of fossil hydrocarbon feedstocks leading to a huge emission of CO2 into the environment. Therefore, it is important to develop green approaches for synthesizing ethylene.
Although very promising results have been reported on ethylene-producing recombinant cyanobacteria, the overall efficiency of the available photoproduction systems is still very low for industrial applications. The ethylene productivity of engineered cyanobacteria is the most critical variable for reducing the costs and improving efficiency.—Sindhujaa Vajravel, lead author
Cyanobacteria have several limitations for efficient production, as they primarily accumulate biomass, not the desired products. They possess a giant photosynthetic light-harvesting antenna that leads to self-shading and limited light distribution in suspension cultures, which decreases productivity. The greatest limitation is that the production period of the cells is short, only a few days, explained Associate Professor Allahverdiyeva-Rinne, a co-author of the paper.
To solve these two problems, the researchers entrapped ethylene-producing cyanobacterial cells within thin-layer alginate polymer matrix. This approach limits cell growth strongly, thus engaging efficient flux of photosynthetic metabolites for ethylene biosynthesis. It also improves light utilization under low-light conditions and strongly promotes cell fitness.
Sindhujaa Vajravel, Sema Sirin, Sergey Kosourov and Yagut Allahverdiyeva (2020) “Towards sustainable ethylene production with cyanobacterial artificial biofilms” Green Chem. doi: 10.1039/D0GC01830A