Chemical regulation of microbial nitrogen cycle

Huge amounts of nitrogenous fertilizer, which are produced through the synthetic ammonia process (Haber-Bosch process) developed in Germany by Fritz Haber and Carl Bosch in 1906, has made it possible to meet the food demand for a global population of more than 7 billion people. At the same time, significant amounts of nitrous oxide (N2O) emitted from fertilized agricultural soils have been found to be produced by microbial denitrification, called anaerobic respiration. Nitrous oxide has considerably high global warming potential and has been considered one of the greatest environmental threats to the near future at a level equal to carbon dioxide. In particular, it has gradually been becoming obvious that denitrification by fungi is the dominant source of nitrous oxide in agricultural soils. The cause is that, unlike bacterial denitrification, the end product of fungal denitrification is nitrous oxide due to lack of nitrous oxide reductase (N2Or), the enzyme that catalyzes the last step of the denitrification pathway (Figure 1). Therefore, fungal denitrification needs to be controlled in order to prevent nitrous oxide emission from agricultural fields. In our laboratory, we have taken up the challenge of developing fungal denitrification inhibitors by chemical screening and then, using a molecular biological approach, elucidate the detailed molecular mechanism of fungal denitrification which still remains unknown in many aspects so as to lead to the development of a more effective system of control of fungal denitrification.



Figure 1. We will contribute to environmental and resource sustainability through chemical biology.
Nowadays, huge amounts of chemical fertilizer (ammonium sulfate and potassium nitrate), produced in factories, have been applied to agricultural soils. However, chemical fertilizers are also taken up by soil microorganisms and utilized for denitrification, called anaerobic respiration. Nitrous oxide (N2O), produced in the denitrification process, is a greenhouse gas with far higher global warming potential than carbon dioxide. N2O concentration in the atmosphere has been dramatically increasing as a result of the introduction of chemical fertilizers into agricultural lands, which is causing serious environmental problems. In our laboratory, we aim to develop denitrification inhibitors targeting NIR or NOR, which is an essential enzyme of the denitrification system, so as to improve the efficiency of nitrogen fertilization and reduce N2O emissions from agricultural soils by adding the inhibitors as nitrogenous fertilizer supplements.