Dr. Keishi Senoo, Professor

Dr. Shigeto Otsuka, Lecturer

Dr. Satoshi Ishii, Research Associate

Dr. Kanako Tago, Research Associate

10 graduate students (2 Ph.D. students, 8 M.S. students) and 3 research students

Our research interests are soil microbial ecology in relation to agricultural and environmental topics.

1. Ecology of denitrifying microorganisms in rice paddy soils

Rice paddy soil is an ecellent agricultural field in terms of low nitrogen pollution: almost no N2O emission and nitrate leaching. These properties of paddy soil are probably due to high activity of N2-generating denitrifiers in soil. They reduce nitrate (NO3-) completely to dinitrogen gas (N2). In contrast, N2O emission and nitrate leaching is a big problem in upland field soils. We are interested in why these two soil types differ significantly in denitrifying activities.

Microbial populations responsible for denitrification in rice field soils are not well characterized. We are currently trying to clarify the community structure of denitrifiers by using several methods: stable isotope probing (SIP), functional gene analysis, and culture-based approach.

2. Molecular ecology of Sphingomonad bacteria in soils

We have maintained an experimental upland field since 1973, to examine long-term effects of pesticide application on the diversity and function of soil microbes. Two kinds of organochlorine pesticides, gamma-hexachlorocyclohexane (HCH) and chlorotaronile (TPN) have been applied once a year.

Degradation rate of gamma-HCH in soil was initially very slow, but it became rapid after three years of application. In 1986, aerobic gamma-HCH decomposing bacterium, Sphingobium japonicum SS86, was isolated from the field. This strain can utilize gamma-HCH as a sole carbon and energy source. The genes responsible for the gamma-HCH decomposition were characterized (linABCD). Several lin genes showed structure of mobile genetic elements, suggesting their alien origin.

We are currently trying to clarify the molecular ecological process of how the gamma-HCH decomposing bacterium acquired the genes in only three years of pesticide application.

3. Isolation of Not-yet-cultured bacteria from soil

Alghough diverse species were present in soil, majorities of them are still not-yet-cultured. We are developing a new methodologies to isolate not-yet-cultured microbes from soil.

For inquiry, please send an email to Dr. Senoo.