Hisaya Kojima

icroorganisms and material circulation in the natural environment

Hisaya Kojima , Assistant Professor,

Institute of Low Temperature Science

High school : Saitama Prefectural Tokorozawa Kita High School

Academic background : Doctorate at Tokyo Metropolitan University

Research areas
Microbial ecology
Research keywords
microorganisms, material circulation, freshwater lakes

What are you aiming to achieve?

Many diverse elements are circulating on the earth, changing their form all the time. This circulation is made possible by the action of organisms, and among them, microorganisms are thought to play a particularly major role. One of the main reasons for this is that microorganisms have extremely diverse capabilities. We humans and other animals eat organic products created by other organisms, and combine them with oxygen to acquire energy. Microorganisms have endless combinations equivalent to our oxygen + organic matter. The role played for us by oxygen may be played by sulfate ions, nitrate ions or carbon dioxide. Furthermore, hydrogen, ammonia, methane or hydrogen sulfide may be used instead of organic matter. These substances have different physicochemical characteristics, and depending on the substance, their toxicity can vary. Microorganisms use these substances and convert them into other compounds, and this is a major driving force in element circulation. The network of mutual interactions formed from the diversity of microorganisms and the diversity of substances is extremely complex. Little is known as yet about material circulation by microorganisms, and our aim is to deepen understanding of this even a little, and contribute to explaining the whole.


What methods do you use in your research?

Photo 1 Lake Okotanpe (Chitose City), one of our major survey sites

I am interested in what is happening in the natural environment, so I begin my research by doing surveys outdoors. Recently I have been looking mostly at freshwater lakes (Photo 1). Once in location, I first look at the quantity of substances that microorganisms create and consume. Following the spatial distribution of, and changes in time to, substances in the water and the mud at the bottom of the lake, it is possible to understand what is happening where (Photo 2). Next, we look at what types of microorganisms are present. Microorganisms are extremely small and cannot be distinguished visually, so we do a kind of DNA testing in order to identify the types of microorganism living in that place. Even if we identify the microorganisms that are present using DNA analysis, it is still difficult to know what they are doing there. Each microorganism only engages with a very small number of substances in the outside world. Furthermore, in a situation where many microorganisms are mixed together, it is impossible to say which microorganism is doing what. In order to investigate what the microorganisms are doing, we need to culture them in the laboratory and create a situation where nothing is present other than the microorganism on which you are focusing. This involves using something called “pure culture”, which is vital in order to understand the nature of a microorganism. Of the many diverse microorganisms present on the earth, only a few have so far been successfully obtained in pure culture. Creating pure culture of new microorganisms, and investigating their nature is an important part of our research (Photos 3/4).


What are you aiming to achieve next?

Photo 2 A device to lift mud from the floor of the lake without disturbing its structure.


There are still many microorganisms left in the environment whose presence we are aware of, but whose function we still do not understand. It is one of my main objectives to clarify how these microorganisms live. Furthermore, some of the conversion reactions implemented by microorganisms on substances have still only been theoretically assumed, and not actually confirmed as true. We aim to detect these reactions in the environment, and identify the organisms that are actually performing them. Finally, we want to culture these microorganisms, and after examining their nature in detail, ideally be able to connect that to an understanding of things that go on in the world around us.

Photo 3 Culturing unknown microorganisms, with the aim of identifying them

Photo 4 An experiment designed to obtain pure culture