Shunta Kimura

A terrestrial cyanobacterium, Nostoc sp. HK-01 has several unique abilities: photosynthesis, nitrogen fixation and tolerance to space. The functions of Nostoc sp. HK-01 as a food resource in extraterrestrial environments such as Mars were investigated for future extraterrestrial agriculture, "Space Agriculture". The nutritional energy of 100 g dry weight of Nostoc sp. HK-01 was estimated to be 358.1 ± 10.9 kcal by the results of protein, sugar and lipids. Six kind of recipes cooked using cyanobacteria were demonstrated and these results indicate that Nostoc sp. HK-01 has three food functions: primary (nutritional), secondary (sensory), tertiary (physiological). We will discuss the utilization of Nostoc sp. HK-01 as a food resource in closed bio-ecosystems. Our results may contribute to the supply of food resources under severe conditions for life-support in closed bio-ecosystems.

A terrestrial cyanobacterium, Nostoc sp. HK-01, is a candidate material for introduction to extraterrestrial environments, such as Mars, given its high tolerance to drought and other extraterrestrial environments. Here, we evaluated Nostoc sp. HK-01 as food for future habitation of Mars. We found that wet colonies of Nostoc sp. HK-01 after initiation survived for over 8 years on Martian regolith simulant (MRS), although they did not survive for over 105 days on medium without MRS. Total protein per 100 g of the dried colony of Nostoc sp. HK-01 was approximately 50 g. Increases in biomass proliferation in liquid or on agar medium were determined in six strains of terrestrial cyanobacteria, including Nostoc sp. HK-01, N. commune HK-02, N. commune YK-04, N. punctiforme ATCC 29133, Brasilonema sp. HK-05 and Calothrix sp. HK-06. Nostoc sp. HK-01 grew better compared to the other five strains under both conditions. Following the incubation of Nostoc sp. HK-01, the medium exhibited radical-scavenging activity. Sugar content in the medium after a 1-day incubation of Nostoc sp. HK-01 was one-sixth of its dry weight at initiation. These results indicate that, after liquid incubation, the remaining cells may be used as recyclable materials on Mars.

The heat tolerance of dry colonies of a terrestrial cyanobacterium, Nostoc sp. HK-01 by exposure to temperatures at 100 °C, the boiling point of liquid water, was examined. The cells of Nostoc sp. HK-01 can live under these conditions for 10 hours. All of the viable cells were akinetes which are dormant cells. Akinetes have a high tolerance to high temperatures. The photosynthetic ability of cells of HK-01 was normal even after the heat exposure. The percentage of decreased water content in the dry colony was 5 percent during the heat exposure for 24 hours. The reasons for the decrease in the percentage of survival rates of colonies under the high heat condition are related to the remaining water in the dry colony, and/or, DNA damage of individual cells. Furthermore, there is a possibility that there are highly tolerant cells in the dry colony since there are cells that survived over 24 hours after the heat exposure.