Japanese researchers have modified blue-green algae to produce and excrete fatty acids through photosynthesis. These fatty acids can serve as a feedstock for biofuels, including sustainable aviation fuel and diesel alternatives.
In science, blue-green algae are called cyanobacteria. They are not true algae, but photosynthetic bacteria. The study appeared in Biotechnology for Biofuels and Bioproducts.
Harvesting makes algae fuels expensive
Blue-green algae have long been considered an interesting source for biofuels. They use light and carbon dioxide to produce energy-rich substances and do not occupy agricultural land that is also needed for food production.
In many existing research lines, these substances remain stored in the cell. As a result, large quantities of organisms must be harvested, concentrated, dried, and broken open before the usable molecules become available. This makes production complicated and expensive.
The team led by Professor Yoshitaka Nishiyama of Saitama University therefore chose a different route. The researchers wanted the blue-green algae not only to produce the fatty acids but also to release them themselves. This way, the cells do not have to be destroyed first to recover the raw materials.
Three interventions in the cell
The researchers worked with Synechococcus elongatus PCC 7942, a cyanobacterium often used in photosynthesis research. They modified three processes in the cell.
A gene that normally redirects fatty acids back into metabolism was deactivated. In addition, they strengthened two endogenous systems. One releases fatty acids from cell membranes, the other helps to transport those fatty acids out of the cell.
The researchers used a so-called self-cloning approach. No foreign genes are required in the final strain. This is important because, in some countries, such organisms may be assessed differently from genetically modified microorganisms in which foreign DNA has been introduced. The precise legal treatment varies by country.
Highest yield at 25 degrees
The modified cyanobacteria clearly excreted more free fatty acids than the untreated control field. The best-performing strain reached 389 milligrams per liter of culture fluid after twenty days. The production rate was 24,7 milligrams per gram of dry cell mass per day.
The highest yield was measured at 25 degrees Celsius and strong continuous lighting. This is remarkable, because this cyanobacterium normally grows faster at a higher temperature of approximately 32 degrees. According to the researchers, a lower temperature can enhance fatty acid production per cell.
Collect fatty acids directly from the liquid
To recover the secreted fatty acids, the researchers applied a thin layer of isopropyl myristate on top of the culture medium. The fatty acids migrated to this top layer, while the blue-green algae continued to live in the aqueous part. In this way, the molecules produced during cultivation could be collected.
That method is not yet suitable for large-scale application. The researchers themselves state that isopropyl myristate is too expensive for this purpose. Therefore, cheaper methods are needed to extract the fatty acids from the liquid. It also remains to be seen how the modified blue-green algae perform under outdoor conditions, where light and temperature change constantly.
Less dependent on heavy post-processing
The study shows that blue-green algae can not only produce fuel feedstocks but also excrete them. This shifts part of the processing from harvesting and breaking open cells to recovering fatty acids from the culture fluid.
That does not yet solve the economic challenges of algae fuels. However, the research does show where significant gains can be made: less heavy post-cultivation and a more direct route to usable molecules.
Source: Eurekalert.org
Photo: ruixue, Adobe Stock
