OS2-3
微細藻類を用いた資源循環型食料生産の実用性検討
Potential for a resource-recycling food production systemusing microalgae
豊川 知華 1, 山田 康嗣 1, 鈴木 健吾 1,Chihana TOYOKAWA1, Koji YAMADA1, and Kengo SUZUKI1
1

株式会社ユーグレナ，Euglena Co., Ltd.,

1. Introduction
To minimize the supply of resources for a long-term human stay on the Moon, it is essential to establish aresource circulation system in a closed environment, especially for efficient food production with limited localresources. The use of plants and microalgae, photosynthetic microorganisms, in this circulation system isexpected to efficiently retrieve resources from the waste. In particular, plants and microalgae fix CO2 released
into closed habitats by photosynthesis and generate oxygen. In addition, they utilize nitrogen and phosphorus
in human domestic wastewater to grow and produce protein and various other nutrients. This paper describes
the characteristics of representative microalgae that are expected to become resource-recycling foods on theMoon.
2. Role of Microalgae in Air Revitalization System
In the International Space Station (ISS), the CO2 removal and O2 generation are achieved through thewater electrolysis (2H2O → 2H2 + O2) and the Sabatier reaction (CO2 + 4H2 → CH4 + 2H2O) which areincluded in the Environmental Control and Life Support System (ECLSS). Although a part of hydrogenrequired in the Sabatier reaction is supplied by the hydrogen produced in the O2 generating reaction,additional hydrogen is required to convert all of the CO2 to O2. The imbalance is required to be compensatedby hydrogen supply from out of the closed environment or the capture and storage of excess CO2 1).
A solution to this problem is to use photosynthetic organisms such as plants and algae to produce O2 andfood from CO2 and nutrient-rich waste fluid. In particular, microalgae can be used for highly efficient foodproduction because the space required for biomass production is less than that of crops, continuous harvesting
is possible, and the whole harvested biomass is edible with less waste.
3. Potential of Microalgae as a Resource-Recycling Food
There are examples of microalgae culture tests conducted in closed isolation facilities in various countries
and cyanobacteria (Spirulina) culture in the ISS2). However, microalgae culture methods for low-gravity
environments such as on the Moon have only just begun to be considered. The most suitable algae species andstrains for use on the Moon have not been screened. Furthermore, the microalgae culture methods which are
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appropriate for the low-gravity environment have not been fully investigated3). Table 1 shows thecharacteristics of representative algae species that have been studied in space.
Table 1. Characteristics of representative algae
Euglena gracilis(pH1.5-3.5)
Advantages

1.
2.
3.

4.

Disadvantages 1.

2.

Chlorella vulgaris(pH6.5-7.0)

Arthrospira platensis(pH8.5-11)

1.
Directly utilize ammonium
contained in urine.
Low risk of contamination at2.
pH3.
There is no growth
inhibition by secreted
components at high cell
3.
density.
High efficiency of genome
editing.

Directly utilize urea andammonium contained inurine.
There is no growth
inhibition by secreted
components at high celldensity.
A successful culture on theISS has been reported.

1.

Hydrogen sulfide isgenerated by the transitionto oxygen-deficientconditions.
Accumulates storage
polysaccharides notabsorbed by humans.

Contaminates easily at pH
5-7 and is not suitable forraw consumption.
Cell walls reduce nutrient
absorption.

1.

1.

2.

2.
3.

2.

Low risk of contamination
at pH9-11.
Can be eaten raw.
A successful culture on theISS has been reported.

Cannot directly utilize
urea and ammonium
contained in urine.
Growth is inhibited by thegeneration of freeammonia under alkalineconditions.

For example, the green algae Chlorella and Chlamydomonas, which proliferate rapidly and can utilize urea inurine as nitrogen sources, Euglena, which utilizes ammonium, and Spirulina, which utilizes nitric acid obtained
from the nitrification reaction of plant residues are candidates for the production on the moon. Euglena isespecially nutritious and has high potential as food. It was reported that Euglena contains 30~50% protein in
dry weight, and its amino acid value is 88, higher than Spirulina and Chlorella4). Furthermore, Euglena contains
many minerals and can synthesize all vitamins except vitamins B1 and B12. Utilizing the potential of microalgae,
a highly-efficient food production system in a closed system can contribute to air revitalization and supply ofnutrients that are deficient in vegetables and other plants.
References
1)

J. M. Mansell, M. B. Abney, and L. A. Miller: 41st International Conference on Environmental Systems, ICES 2011–1–
13 (2011), DOI: https://doi.org/10.2514/6.2011-5035

2)

J. Fahrion, F. Mastroleo, C. G. Dussap, and N. Leys: Front. Microbiol. 12, 1–14 (2021),
DOI: https://doi.org/10.3389/fmicb.2021.699525

3)
4)

G. Detrell, Front. Astron. Sp. Sci., 8, 1–10 (2021) DOI: https://doi.org/10.3389/fspas.2021.700579
中野長久、宮武和孝、乾博、穂波信雄、村上克介、金井謙二、辰巳雅彦、相賀一郎、近藤次郎, CELLS 学会誌
Vol.10 No.2 13–24 (1998) DOI: https://doi.org/10.11450/seitaikogaku1989.10.2_13© 2022 by the authors. Submitted for possible open access publication under theterms and conditions of the Creative Commons Attribution (CC BY) license(http://creativecommons.org/licenses/by/4.0/).
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