[H-CG25] Advanced life support systems with closed bio-ecosystems and their applications

[HCG25-P02] Analysis of Gene Expression and Cyanophycin Metabolic Changes during Drying-Rehydration Processes in Nostoc sp. HK-01

*Hayato Koyama¹, Kengo Shibasaki¹, Hiroshi Katoh², Kaori Tomita-Yokotani^3,1, Toshisada Suzuki⁴, Tomoko Abe¹ (1.School of Science and Engineering, Tokyo Denki University, 2.Advanced Science Research Promotion Center, Organization for Research Initiative and Promotion, Mie University, 3.Faculty of Life and Environmental Sciences, University of Tsukuba, 4.Faculty of Agriculture, Kagawa University)

Keywords: cyanobacteria , drought tolerance

Nostoc sp. HK-01 was isolated as a strain of terrestrial cyanobacteria exhibiting exceptionally high desiccation tolerance. In Tanpopo mission experiment, which is included exposure to outside of the International Space Station (ISS), the cyanobacterium can survive in a space environment¹⁾ . This strain is expected to be used in a closed space environment as a material circulation system²⁾ and as a food resource³⁾ in the future. To use this strain, space transportation must be considered for the initial introduction. Lightweight is necessary for space transportation, and desiccation tolerance is an important feature contributing to weight reduction. To utilize desiccation tolerance, it is essential to establish a method for preparing desiccated cells with high desiccation tolerance. In this study, we focused on specifically expressed genes, metabolites, and products during short-term drying and rehydration processes to obtain the knowledge necessary for stable desiccated cell preparation.
Cells of Nostoc sp. HK-01, cultured in BG-11 liquid medium under illumination, were gradually desiccated in a desiccator under dark conditions, and samples were collected at fixed intervals. After that, semi-desiccated cells were re-cultured in BG-11 liquid medium. The samples were used as extraction of RNA, cyanophycin, and free amino acids. Each extraction sample was analyzed. As a result of screening for genes that exhibited specific changes in expression levels during the transitions from hydrated to desiccated states, genes encoding heat shock proteins, proteases, or cyanophycin-degrading enzymes were detected. Furthermore, quantitative determinations of cyanophycin and its degradation products, namely aspartate and arginine, suggested that the metabolism of various amino acids by cyanophycin degradation is enhanced during the rehydration process.

References:
1. Tomita-Yokotani, K. et al., Astrobiology 21, 1506-1514, 2021.
2. Arai M. et al., Biological Sciences in Space 22, 8-17 2008.
3. Kimura, Y. et al., Biological Sciences in Space 29, 24-31 2015.