Graduate School of Biostudies, Division of Integrated Life Science Associate Professor
Photosynthetic microorganisms living in water have not been used much by humans because they are small and rarely seen by the human eye. However, these microorganisms have evolved in various ways, hiding from human sight. Some of them possess traits that are useful to humankind. Using my background in molecular genetics, I am challenging new approaches to research using these photosynthetic microorganisms.
As for the species, we are working with Arthrospira platensis (right photograph) and several other microalgae. A. platensis, commonly known as "spirulina," is an edible multicellular cyanobacterium that can grow under alkaline conditions, making it easy to conduct monocultures without contamination from other algae, even when cultured outdoors. In addition, because of its relatively large size, it can be easily harvested by filtration. Because of these characteristics, industrial mass cultivation of this organism began in the 1970s, and it is currently used worldwide as a raw material for foods and food additives.
However, this microorganism has not been used much as an organism for basic research, and experimental systems for conducting basic research have not been developed well. In our laboratory, we have been developing systems to facilitate the use of A. platensis as a research subject for molecular biological studies. We are also using mutants of A. platensis to study the mechanisms of genetic regulation of growth and morphogenesis. These studies will provide fundamental information for breeding this organism.
Recently, we have determined the full-length genome sequence (approximately 6.8 million base pairs) of a representative strain of A. platensis, strain NIES-39, and published the information (GenBank ID AP026945.2; Shiraishi and Nishida ( 2023)). The information on the genome sequence can be used for various breeding programs to modify the genome of A. platensis.
Why does spirulina have a spiral shape?
The spirulina (Arthrospira species) is characterized by its helicoid shape. When spirulina is placed on a solid medium, it moves around smoothly on the surface of the medium. Such movement is called "gliding movement" in microbiological terminology. Our recent research has revealed that, during gliding movement, spirulina frequently changes the direction of its movement by taking advantage of its helicoid shape. Also, the helicoid structure contributes to keeping its movement speed almost constant even when the temperature changes so that it does not fall into a runaway state. When the morphology of spirulina becomes linear due to mutations, it loses control of its movement and enters a runaway state. Spirulina's helicoid morphology is thought to have evolved this way so that it can control its movement. [Shiraishi et al., 2024]