The impact of microorganisms on climate change

I mainly study the role of microorganisms in lakes and soils, especially in the cryosphere. How are these tiny, invisible microorganisms linked to global climate change? There are many examples.

Microorganisms decompose organic matter such as plant and animal feces and carcasses, the rate of which is generally accelerated by higher temperatures. In other words, the warmer the temperature, the faster decomposition by microorganisms tends to progress. At this time, microorganisms consume the surrounding oxygen to carry out decomposition, so eventually a water body with less oxygen is created. This is called the development of an anaerobic environment. In an anaerobic environment, microorganisms will emit methane gas through decomposition. Methane gas has a greenhouse effect approximately 25 times greater than carbon dioxide, so an increase in methane gas emissions into the atmosphere will further accelerate global warming.

In addition, in the Arctic regions of Siberia and Alaska, for example, there are large stores of methane gas produced by former microorganisms under permafrost. Therefore, the melting of permafrost due to global warming could also release methane gas into the atmosphere.

In fact, there are still many unknowns, such as whether these methane gasses enter the atmosphere in their entirety, or whether the balance is maintained to some extent due to consumption by some microorganisms. There is also the special phenomenon of ‘red snow’, which I will talk about later. Unraveling these complex connections one by one is one major objective of microbial research in climate change.

How to test for microorganisms

To examine unknown microorganisms, we can of course look at them under a microscope or even culture them to increase their numbers, but this is not enough. The first thing to look at is the genes in the microorganism which synthesize a protein called the ribosome. By analyzing these ribosomal genes, we can determine the phylogenetic relationships of microorganisms and how many of them are present in the environment.

The next thing we want to know is what functions the microorganism has and how it is connected to the surrounding ecosystem. To know this, we need to analyze the genome of the microorganism, which is quite a challenge. For example, there are tens of thousands of microorganisms living in the soil, so we need to reconstruct the genome of every single one of them. In modern times, full-length genomes are analyzed using a technique called bioinformatics, and their elements are painstakingly examined.

Ecosystems found in the red snow

I participated in the 47th Antarctic Expedition in 2006. During that expedition, I found a strange phenomenon while walking along the Antarctic coastal zone.

There was a reddish area at the end of the pure white glacier. Curious, I took a sample and looked at it under the microscope and found that it was a phenomenon known as ‘red snow.’ Red snow is a phenomenon in which algae produce red pigments to protect their DNA from the strong ultraviolet rays of the summer polar regions, cutting out UV rays like sunglasses. The red color is due to a carotenoid pigment called astaxanthin.

Red snow is also closely linked to climate change. The coloring of the white ice tops that normally reflect sunlight may accelerate snow cover and glacier melting. There are reports that the period during which red snow can be observed has increased in recent years.

Curiously, if there are algae, then there must also be microorganisms living there that eat the organic matter produced by the algae. So we took samples back to the laboratory to check its genes and found that it was, in fact, inhabited by a large number of heterotrophic bacteria. About 10 years later, we succeeded in isolating and culturing it and registered it as a new species, Hymenobacter nivis. The name ‘Nivis’ means snow. We believe that this is an achievement unique to the Institute of Low Temperature Science.

I wondered how such ecosystems can be nurtured on empty ice, and investigated it with a geo-organic chemist who had been on the Antarctic expedition with me. It turns out that birds that eat krill and other fish in the ocean fly over and drop their feces on the ice. We found that the organic matter and nutrients contained in these droppings support the ecosystem of the red snow.

Microbes are key organisms in the ecosystem. We were able to visualize the connections between them and the various organisms around them. These discoveries are really fascinating.

Diverse lakes and their lifespans

The lakes I have studied include Lake Okotanpe in Hokkaido, the Sugatamino Pond in Asahidake and Lake Harutori in Kushiro. Outside Hokkaido, I have also conducted research at Lake Mizugaki in Yamanashi Prefecture, and Fei-ts’ui Reservoir in Taiwan.

Lakes, sometimes called ‘microcosms,’ are compact and independent compared to the oceans, making them relatively convenient for revealing how ecosystems work. I like to study lakes in the hope that the findings obtained in them can be applied to the oceans.

And even when lakes look exactly the same, they are very diverse in their inner workings. Some, like Lake Biwa, are low in nutrients, while others, like Lake Teganuma in Chiba Prefecture, are highly polluted. In the case of Lake Harutori, seawater and freshwater are mixed together, so the question was what kind of ecosystem exists in the lake.

With such a variety of perspectives, it is fun to do research and think about what the characteristics of this lake are.

In 1951, Dr. Masao Minato of Hokkaido University wrote a book entitled ‘The Life of a Lake’. It is a book for children about the spreading of lakes over a long period of time and their eventual transformation into marshland or land. It is exactly like that, and it is also fun to look at it from the point of view of what stage of the lake I am currently researching, as it can reveal the characteristics of the lake over a long geological age.

Seeing broadly and deeply in time

The Earth’s environment has gradually evolved over the 4.6 billion years since its formation to its present state. Since the first life forms emerged some 4 billion years ago, life forms and the global environment have co-evolved and changed. This has resulted in the diversity of the global environment as we know it today.

In other words, by looking at the whole wide globe and carefully studying the diverse environments that exist within it, we can also obtain information about the distant past, when humans did not even exist. In fact, my field encompasses the Arctic to Antarctica, so microorganisms may be telling us about the time of the snowball, when the Earth was frozen globally, for example. In this light, I believe that research in the Antarctic snow and ice region may also provide suggestions for climate change countermeasures. With this in mind, I enjoy my research every day.

Written by Space-Time Inc.

Published on September 19, 2024