First Algal Breeding Technology to Use Neutron Beam Irradiation

Seagriculture USA 2024
Neutron Beam Irradiation

Schematic representation of facility for a high-energy neutron beam. Boron carbide and silicone rubber were placed to reduce thermal neutrons. 50 mL tubes containing algal culture were located at an indicated distance from the neutron production target.

NTT Corporation (NTT) and Euglena Co., Ltd. (Euglena) have succeeded, they say, for the first time in the world, breeding algae by mutagenesis using neutron beam irradiation. This achievement is expected by the researchers to be a fundamental technology that will solve various issues related to climate change by improving the amount of CO₂ absorbed by algae and by breeding and producing algae that are useful for various purposes. The results were published in the scientific journal Scientific Reports on July 3, 2024.

In the past, algal breeding methods have attempted mutagenesis using electromagnetic waves and heavy particle beams, which have low permeability to substances containing water, such as culture medium, and have not been effective against most algal cells growing in culture medium.

Instead, NTT and Euglena Co. focused on neutron beams that have no electric charge and are highly permeable to substances containing water such as culture medium. Consequently, since 2022, NTT and Euglena Co. have been conducting a joint research project aiming to establish algal breeding technology by using two types of neutron beams:
1. high-energy neutron beams and
2. thermal neutron beams

Optimization of neutron beam irradiation conditions

For the first time, the team clarified the relationship between the type of neutron beam (high-energy neutron beam or thermal neutron beam) and the absorbed dose, and the mutagenesis efficiency of algal genes.

The mutation was evaluated using the unicellular alga Cyanidioschyzon merolae (Cyzon), based on a mechanism in which a mutation in a gene that synthesizes nucleic acids allows growth on agar medium containing a drug that inhibits growth. The analysis revealed that mutations were most effectively introduced at 20 Gy irradiation for high-energy neutron beams and at 13 Gy irradiation for thermal neutron beams.

Next, they analyzed the mutation patterns caused by the optimized irradiation conditions. As a result, about 90% of the mutation patterns of the genes in which mutations were introduced were substitutions, deletions, and insertions of the 1 nucleotide sequence, and about 10% were changes of two or more nucleotide sequences. There is a report that the change of two nucleotide sequences or more is about 30% by gamma ray (γ-ray), suggesting that the mutation pattern caused by neutron beam irradiation is different from the current method.

Isolation of algae with improved oil production

By applying the optimum neutron beam irradiation conditions to Euglena gracilis (Euglena), the researchers succeeded in breeding strains that produce up to 1.2 to 1.3 times more oil than the wild type strain.

The optimum neutron beam irradiation conditions identified by Cyzon were applied to Euglena, one of the commercial algae that produce biofuels (equivalent to jet fuel or diesel fuel), to acquire cells with improved oil production.

Fluorescent dye, which specifically stains oils, was added to cells irradiated with neutron beams to stain the oils, and the strength of the amount of fluorescence emitted by each cell was used as an indicator for selection. As a result, they succeeded in acquiring four strains with higher oil production than the wild type strain.

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Seagriculture USA 2024
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