TY - JOUR
T1 - CH 4 oxidation-dependent 15 N 2 fixation in rice roots in a low-nitrogen paddy field and in Methylosinus sp. strain 3S-1 isolated from the roots
AU - Shinoda, Ryo
AU - Bao, Zhihua
AU - Minamisawa, Kiwamu
N1 - Funding Information:
The work was supported by grants from the Ministry of Agriculture, Forestry and Fisheries of Japan ( PMI-0002 , BRAIN) and by Grants-in-Aid for Scientific Research (A) 23248052 , (A) 26252065 and (B) ( 18H02112 ) from the Ministry of Education, Culture, Sports, Science and Technology of Japan and by grant from the National Natural Science Foundation of China (No. 41563009 ). We thank T. Tokida (Institute for Agro-Environmental Sciences) for providing the difluoromethane gas and S. Asakawa (Nagoya University) for advice on methanotroph isolation.
Publisher Copyright:
© 2019
PY - 2019/5
Y1 - 2019/5
N2 - Methane (CH 4 ) oxidation and nitrogen (N 2 ) fixation are simultaneously activated in the roots of rice plants grown in paddy fields with low N input (LN). However, the mechanism of CH 4 oxidation-dependent N 2 fixation remains largely unknown. In the present study, a 15 N 2 -feeding experiment was adopted to evaluate methanotrophic N 2 fixation in LN rice roots and in a methanotroph isolated from the rice roots. The presence of CH 4 significantly enhanced 15 N incorporation from 15 N 2 gas in LN rice roots, indicating methanotrophic N 2 fixation. Methylosinus sp. strain 3S-1 was isolated from LN rice roots, and it grew well in N-free liquid medium under different levels of oxygen stress (2%, 10%, and 20% O 2 ). N 2 fixation of strain 3S-1 was directly measured using 15 N in biomass; when 3S-1 cells were exposed to a gas mixture consisting of 15 N 2 (35%), CH 4 (5%), and O 2 (2% or 10%) in argon (Ar) balance, the 15 N concentration in the cells rapidly increased at both O 2 concentrations. The addition of difluoromethane, a potent inhibitor of methane monooxygenase, immediately stopped CH 4 oxidation and reduced the 15 N enrichment rate, indicating that N 2 fixation depended on CH 4 oxidation in pure culture. These results suggest that N 2 fixation was stimulated by CH 4 oxidation in LN rice roots and that type II methanotrophs in LN rice roots, including Methylosinus, are responsible for CH 4 oxidation-dependent N 2 fixation.
AB - Methane (CH 4 ) oxidation and nitrogen (N 2 ) fixation are simultaneously activated in the roots of rice plants grown in paddy fields with low N input (LN). However, the mechanism of CH 4 oxidation-dependent N 2 fixation remains largely unknown. In the present study, a 15 N 2 -feeding experiment was adopted to evaluate methanotrophic N 2 fixation in LN rice roots and in a methanotroph isolated from the rice roots. The presence of CH 4 significantly enhanced 15 N incorporation from 15 N 2 gas in LN rice roots, indicating methanotrophic N 2 fixation. Methylosinus sp. strain 3S-1 was isolated from LN rice roots, and it grew well in N-free liquid medium under different levels of oxygen stress (2%, 10%, and 20% O 2 ). N 2 fixation of strain 3S-1 was directly measured using 15 N in biomass; when 3S-1 cells were exposed to a gas mixture consisting of 15 N 2 (35%), CH 4 (5%), and O 2 (2% or 10%) in argon (Ar) balance, the 15 N concentration in the cells rapidly increased at both O 2 concentrations. The addition of difluoromethane, a potent inhibitor of methane monooxygenase, immediately stopped CH 4 oxidation and reduced the 15 N enrichment rate, indicating that N 2 fixation depended on CH 4 oxidation in pure culture. These results suggest that N 2 fixation was stimulated by CH 4 oxidation in LN rice roots and that type II methanotrophs in LN rice roots, including Methylosinus, are responsible for CH 4 oxidation-dependent N 2 fixation.
KW - Methanotroph
KW - Nitrogen fixation
KW - Rice paddy
KW - Stable isotope analysis
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U2 - 10.1016/j.soilbio.2019.01.021
DO - 10.1016/j.soilbio.2019.01.021
M3 - Article
AN - SCOPUS:85061105474
SN - 0038-0717
VL - 132
SP - 40
EP - 46
JO - Soil Biology and Biochemistry
JF - Soil Biology and Biochemistry
ER -