Academia Sinica Logo

The research team of Dr. Sen-Lin Tang from the Biodiversity Research Center has confirmed the coupling between methane oxidation and nitrogen fixation, which may benefit in designing better sustainable management of rice fields, especially in the reduction of greenhouse gas methane. This study was published in May 2022 in mBio. 

Methanotrophic bacteria are capable of removing greenhouse gas CH4 by methane oxidation; moreover, type II methanotrophic bacteria (a group of Alphaproteobacteria) can also fix nitrogen according to genomic analysis and pure bacterial cultivation-dependent studies. However, methane oxidation requires oxygen but nitrogen fixation occurs in anoxygenic conditions. Whether these two “conflict” metabolisms in oxygen requirement can co-occur in a single methanotrophic bacterial cell in the natural environment lacks no direct evidence.

The research team included Dr. Kiwamu Minamisawa from the Graduate School of Life Science of Tohoku University, Dr. Sen-Lin Tang from Biodiversity Research Center, Academia Sinica, and core facility nanometer-scale secondary ion mass spectrometry (NanoSIMS) maintained by Institute of Astronomy and Astrophysics and Institute of Earth Science. The team searched for direct evidence of the co-occurrence mechanism of methane oxidation and nitrogen fixation. They applied techniques of next-generation sequencing, fluorescence in situ hybridization (FISH), and stable isotope probing to this study. We successfully identified type II methanotrophs that were dominantly responsible for both methane oxidation and nitrogen fixation in rice roots. Moreover, in the single bacterial cells, our results proved that type II methanotrophs could perform two metabolic metabolisms simultaneously and showed their metabolic coupling relationship. In the 42 hours culture experiment, methane oxidation activity for every single type II methanotrophic cell exponentially increased. However, nitrogen fixation activity in some type II methanotrophs slowed down after 23-hours of incubation. That suggests the bacteria started sharing fixed nitrogen with the plant host. The research revealed the coupling between methane oxidation and nitrogen fixation in more detail, which may benefit in designing better sustainable management of rice fields, especially in the reduction of greenhouse gas methane.

Contributors for the paper:

Kiwamu Minamisawa’s Lab: Dr. Shintaro Hara (Co-first author), Dr. Meng Zhang (Co-author), Dr. Zhihua Bao (Co-author), Dr. Kiwamu Minamisawa (Co-corresponding author)

Sen-Lin Tang’s Lab: Dr. Naoshia Wada (Co-first author) and Dr. Sen-Lin Tang (Co-corresponding author)

The NanoSIMS Core Lab: Dr. Sliver Sung-Yun Hsiao (Co-corresponding author) and Dr. Der-Chuen Lee (Co-author, Leader of the Core Lab)

Lab of Electron Probe Microanalysis: Dr. Yoshiyuki Iizuka (Co-author)

Figure: A hypothetical scheme for the ecological interactions of type II methanotrophs-plant host-other soil bacteria in the methane oxidation and nitrogen fixation.