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

Ryo Shinoda, Zhihua Bao, Kiwamu Minamisawa

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)40-46
Number of pages7
JournalSoil Biology and Biochemistry
Volume132
DOIs
Publication statusPublished - 2019 May

Keywords

  • Methanotroph
  • Nitrogen fixation
  • Rice paddy
  • Stable isotope analysis

ASJC Scopus subject areas

  • Microbiology
  • Soil Science

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