Lipid production model created by disrupting the starch debranching enzyme in microalgae. Credit: Kato et al. (2021)
Across-institutional collaboration among a research group at Kobe University’s Engineering Biology Research Center has developed a technique to repartition carbon resources from algal carbohydrates into lipids. The goal of the research has been to apply this method to biofuel production.
The research group consisted of Project Assistant Professor KATO Yuichi and Professor HASUNUMA Tomohisa et al., and Senior Researcher SATOH Katsuya et al. at the Takasaki Advanced Radiation Research Institute of the Quantum Beam Science Research Directorate, in Japan.
During their research it was discovered that the majority of carbon resources were diverted to starch production instead of lipid production under light/dark conditions (i.e. day and night). This is a problem when cultivating microalgae species outside.
Research Methodology
The researchers used the ion beam at QST’s Takasaki Advanced Radiation Research Institute to induce mutation in the microalgae. This enabled them to cultivate a new mutant strain called Chlamydomonas sp. KOR1, which can produce large quantities of lipids even in light/dark conditions.
They discovered that this KOR1 strain has disruptions in the starch debranching enzyme gene ISA1, causing it to produce a different carbohydrate: phytoglycogen instead of starch (see microscope image).
Electron microscope image of lipid production in the microalgae Chlamydomonas sp. Credit: Kato et al. (2021)
Normally, microalgae synthesize and accumulate carbohydrates (starch) during light periods and break them down when it is dark. However, many carbohydrates accumulate that cannot be completely broken down. Contrary to this, the carbohydrate synthesized by KOR1 (phytoglycogen) was completely broken down during the dark period. The results of the KOR1 metabolome analysis revealed a total increase in intermediate metabolites in both the starch and lipid synthesis pathways. Intermediate metabolites included fructose-6-phosphate, glucose-6-phosphate, acetyl-CoA and glycerol 3-phosphate.
From this analysis, the researchers illuminated the metabolic mechanism underlying the increased lipid production that resulted from ISA1 gene disruption. In the KOR1 strain, the carbohydrate (phytoglycogen) was quickly broken down and intermediate metabolites subsequently induced the carbon resource to be repartitioned to lipid production (see diagram).
Further Developments
In order to produce biofuels using microalgae, it is necessary to cultivate these organisms outside in the sunlight. However, there is an unavoidable decrease in lipid production under these light/dark conditions. The technique of repartitioning carbon resources by disrupting the starch debranching enzyme gene developed through this research is one answer to this problem. It is hoped that this new method can contribute towards the large-scale implementation of biofuel production using microalgae.
These research results were published on April 9, 2021 in the international academic journal Communications Biology.
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