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Research Interests

Hatching of Volvox carteri

We are investigating the mechanism of growth, development and evolution of photosynthetic microorganisms. We are currently focusing on the study of the edible multicellular cyanobacterium Arthrospira (Spirulina) platensis.

Arthrospira platensis is a filamentous alkalophilic cyanobacterium that has been traditionally consumed as food by people living along the shores of alkaline lakes in several regions in the world. It is one of the most protein-rich food known, as it contains as high as approximately 60% protein in dry weight. Because Arthrospira can be cultured under alkaline conditions where growth of other microalgae is suppressed, it can be cultured outdoors as an almost single algal strain. Because of the easiness of its unialgal cultre, Arthrospira is commercially cultured in many subtropical areas in the world and consumed worldwide as food, food additives, and feed for animals and fishes. It is usually marketed with the name spirulina, which is based on its former scientific name, Spirulina. We are currently focusing on developing tools and technologies for molecular genetic study of this cyanobacterium.

The footage below is from a time-lapse movie of the gliding movement of spirulina (A. platensis NIES-39).

Why does spirulina have a spiral shape?

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]

Selected Publications

For other works, please see List of Publications.

H. Shiraishi started his research in a laboratory linked to the so-called "phage group". He is perhaps the last generation who was able to start his research in the reverberation of the Phage Group.