Professor Hiroyuki Yamaguchi

Affiliation: Graduate Faculty of Health Sciences /Graduate Graduate School of Health Sciences (Department of Health Sciences, School of Medicine)

Expertise: Microbiology

Keywords of research: protist, symbiosis, chlamydia, microcosm, microbial interaction

Alma mater: Nihon University Second High School (Tokyo)

Final academic background: Faculty of Health Sciences, Kyorin University

*This article was originally published in the 4th issue of "Frontiers of Knowledge" and has been re-edited for the web.

What are you aiming for?

Although we cannot see it with the naked eye, there are countless microorganisms such as bacteria, protists, and fungi that continue to live in a complex and bizarre struggle with each other. It's not just the mouth, the intestinal tract and the skin. In the soil of the schoolyard, on the desk, in the kitchen, on the dining table, in the basement, and in the air you just breathed. What the hell are you doing? Bacteria were born more than 3 billion years ago, and have survived to the present day. Human beings probably enjoy immeasurable benefits from the microbes around us, but unfortunately, we still do not fully understand the role they have played. We have learned so far from the battle between bacteria and protozoa (amebas), the indoor microbiome (what kind of microorganisms are there and to what extent), and from the work of visualizing the microecosystems around us. We are trying to find universal life phenomena that are constantly occurring among microorganisms that have not been discovered.

What kind of equipment did you actually use, what kind of experiments did you do, and what did you learn?

What we learned from verification experiments in the Sapporo Underground Walking Space


Have you ever taken a walk through the 520m underground walking space from Sapporo Subway Station to Odori? In the evening, a flood of people come and go from the subway ticket gates. How does crowding affect the microbes that live there? Therefore, we actually used a machine called an air sampler to collect and verify the air in the underground walking space over time (from May to July) (Photo 1: Air sampler actually in operation). . The analysis results were very complicated, but it seems that as the temperature and humidity rise, the number of fine particles suspended in the air increases, which may induce bacteria to be released from passers-by. This is very useful information for maintaining a sanitary indoor environment.

Ciliates facilitate horizontal gene transfer between bacteria

Do you know a protist called ciliate, which is about 20 micrometers? They are ubiquitous microorganisms found in the soil, ponds, and river water around us. Although it feeds on bacteria, it is well known as a voracious eater that munches on the surrounding bacteria. We wondered if the bacteria around us were just being eaten and weren't doing us any favors. In fact, when ciliates eat bacteria, it is known that they pack a large amount of bacteria into a small bag and spit it out. Therefore, we hypothesized and tested the hypothesis that horizontal gene transfer between bacteria might be promoted by densely packing bacteria in one place. As a result, it was found that, as expected, when the two types of bacteria and ciliates are mixed and cultured, the bacteria taken up by the ciliates are packed into one bag, promoting the conjugative transfer frequency (Photo 2: red). and green-labeled E. coli were packed into a single vesicle and turned yellow). This result is very important in considering the ``place'' in which bacteria acquire diversity in the environment.

Photo 2

Amoeba repels legionella, a natural enemy of amoeba (a pathogenic bacterium that causes pneumonia in the elderly)

There are amoebas that live with symbiotic bacteria in their cells. Among them, there was an amoeba that became healthy when the symbiotic bacteria was removed. This symbiotic bacterium has almost no enzymes that control the TCA cycle, so it cannot leave progeny outside this amoeba. This amoeba uses tremendous energy to allow the symbiosis of this bacterium. Why? We compared susceptibility to amoeba's natural enemy, Legionella, with eradicated amoeba. As a result, they discovered that legionella is less likely to infect amebas, which are symbiotic with bacteria, compared to eradicated amebas 3 . It seems that amoeba and symbiotic bacteria are living together, coexisting with each other very well.

What are you aiming for now?

Our research is just beginning. The conflict between protists and bacteria suggests that microcosms are more complex than we imagine. On the other hand, our research results to date have provided many hints for elucidating the dynamics of the microcosmies around us and for protecting humans from infectious diseases. By taking advantage of interactions between common microbes around us, we may be able to better control pathogens that attack humans and predictably prevent infectious diseases. In the near future, the time may come when we no longer need antibacterial agents!

Reference book

  1. Okubo T, Osaki T, Nozaki E, Uemura A, Sakai K, Matushita M, Matsuo J, Nakamura S, Kamiya S, Yamaguchi H. Walker occupancy has an impact on changing airborne bacterial communities in an underground pedestrian space, as small-dust Particles increased with raising both temperature and humidity. PLoS One. 2017 Sep 18;12(9):e0184980.
  2. Matsuo J, Oguri S, Nakamura S, Hanawa T, Fukumoto T, Hayashi Y, Kawaguchi K, Mizutani Y, Yao T, Akizawa K, Suzuki H, Simizu C, Matsuno K, Kamiya S, Yamaguchi H. Ciliates rapidly enhances the frequency of conjugation between Escherichia coli strains through bacterial accumulation in vesicles. Res Microbiol. 2010 Oct;161(8):711-9.
  3. Ishida K, Sekizuka T, Hayashida K, Matsuo J, Takeuchi F, Kuroda M, Nakamura S, Yamazaki T, Yoshida M, Takahashi K, Nagai H, Sugimoto C, Yamaguchi H. Amoebal endosymbiont Neochlamydia genome sequence illuminates the bacterial role in the defense of the host amoebae against Legionella pneumophila. PLoS One. 2014 Apr 18;9(4):e95166.