Frontier Sciences
Shinichiro Maruyama

 

Small Symbiosis, Big Impact

I am studying the mechanisms of symbiotic relationships among organisms. I have always had a hard time socializing with people, and it is no exaggeration to say that my research on symbiosis is related to my bitter past, in which I have always envied other living things that live in harmony with each other in the natural world. An exaggeration, perhaps? No... yeah, it’s still an exaggeration. I literally said too much. That’s not the case at all. Well, it is true that I am not good at socializing, but that is not why I started studying symbiosis. Furthermore, we cannot tell from the appearance alone whether organisms are living together in harmony. It is only human ego that makes us envious of them.

Our goal is to uncover the scientific mechanisms underlying symbiotic relationships between photosynthetic microorganisms and their hosts—commonly referred to as photosymbiosis—and articulate these processes in molecular and evolutionary terms, beyond everyday language. To this end, we are conducting research using diverse biological systems, including host organisms such as corals, sea anemones, hydra, and amoebas, along with microalgae that live symbiotically within them. For example, how do microalgae, known as symbiotic algae that live in corals, transfer sugars—a product of photosynthesis—to their hosts? This simple question led to investigation, which further led to the discovery of a new pathway by which algae release sugars outside the cells. The level of activity of this pathway is such that the surrounding environment is affected by changes in activity, regardless of whether a host organism is present or not. In other words, for the coral symbiotic algae this is simply a part of their environmental response. However, for the surrounding organisms, it is like a windfall, allowing them to enjoy some crumbs. It is thought that this exchange of nutrients, which occurs as a kind of force majeure, is the key to supporting the establishment of symbiosis. Studies are investigating the environmental conditions under which microalgal symbiosis enhances host-organism growth rates and how such benefits may serve as evolutionary drivers for the development and persistence of symbiotic relationships. These are merely weak interactions between tiny organisms; however, if we zoom out and look at them from a distance, we can ask the question of how the carbon dioxide fixed by microalgae through photosynthesis flows within the ecosystem. Controlling carbon flow is the key to establishing symbiosis. It can be said that it creates the individuality of each symbiotic system and shapes the diverse carbon flows in the ecosystem.

Research results to date have only provided a handful of hints and are far from fully understanding the mechanisms of symbiosis and the carbon cycle within ecosystems. Still, I find myself honestly saying “This is fun!” I enjoy my research every day, vaguely thinking that if I continue to do what I think is right, the world might change just a little someday.

“I can’t do anything.
Is it really something to be proud of that I even noticed?
There are nights that never end
in my head”*²

*¹ *² Excerpts from the lyrics of “Yoake No Uta” by ZOOKARADERU, translated into English by the author.