1. Iron-reducing diazotrophs
Japanese agronomists often say that “wheat grows on fertilizer, while rice grows on soil fertility,” reflecting the traditional observation that paddy rice grows relatively well even without nitrogen fertilizer, unlike upland crops. This indicates that rice production relies strongly on the inherent nitrogen fertility of paddy soils. A central mechanism supporting this fertility is biological nitrogen fixation, in which soil microorganisms convert atmospheric N₂ into ammonia. Historically, Cyanobacteria and root-associated Alpha- and Betaproteobacteria have been recognized as the major diazotrophs in paddy soils. Recently, however, we found that iron-reducing bacteria constitute a previously overlooked but predominant group of nitrogen-fixing microorganisms that play a key role in maintaining the nitrogen fertility of paddy soils.
Publications 1, 4, 5 etc.
2. Enhancement of N fixation in paddy soils
Rapid population growth has sharply increased global food demand, accompanied by a substantial rise in nitrogen fertilizer consumption. However, excessive nitrogen fertilization has led to nitrogen pollution, such as nitrate leaching into groundwater and emissions of nitrous oxide to the atmosphere, thereby worsening environmental problems. Under these circumstances, there is an urgent need to establish sustainable cropping systems that rely less on nitrogen fertilizers.
To address this challenge, we initiated research aimed at enhancing the nitrogen-fixing activity of the iron-reducing bacteria we discovered. Specifically, we attempted to stimulate nitrogen fixation by applying iron oxides—used by iron-reducing bacteria as electron acceptors—to paddy soils. This approach proved successful both in paddy soil microcosms and in actual field trials, and we are currently advancing efforts to implement it in agricultural practices with lower dependence on nitrogen fertilizers.
Publications 8, 9 etc.
3. Iron morphology
Content coming soon
4. Metagenomics/Metatranscriptomics
We were the first in the world to conduct metagenomic and metatranscriptomic analyses of paddy soils, revealing that members of the families Anaeromyxobacteraceae and Geobacteraceae within the class Deltaproteobacteria are major drivers of reductive nitrogen transformation processes, including nitrogen fixation, multiple steps of denitrification, and DNRA. We also comprehensively identified the microbial taxa involved in the key reactions of methane metabolism—such as substrate production, methanogenesis, and methane oxidation—that are highly active in paddy soils.
At present, we continue to address the fundamental question of “who is doing what, and where” in paddy soils by applying integrated metagenomic and metatranscriptomic approaches.
5. Management of crop cultivaition in greenhouses
Content coming soon