Methanogenic Archaea and Methanotrophic Bacteria in a Subtropical Paddy Field and Their Interaction: Controlling Methane Emissions from Paddy Fields.

Abstract

In flooded rice fields, methanogenic archaea produce CH 4 , while methanotrophic bacteria oxidize a part of the produced CH 4 . Thus, the latter bacteria are considered as suitable organisms for controlling CH 4 emission from paddy fields. In this paper, the author demonstrates a case of organic matter application, enumeration and isolation of methanogenic archaea and methanotrophic bacteria in a subtropical paddy field. The rice rhizosphere is one of the typical areas where anaerobic and aerobic environments interface, methanogens produce CH 4 and methanotrophs utilize it for energy. Although how they interact in the anaerobic and aerobic interfaces is an attractive research area, it has not yet been fully elucidated, because a two-member co-culture of methanogen and methanotroph is not well developed. Co-culture of a strictly anaerobic methanogenic archaeon and an obligately aerobic methanotrophic bacterium using sterilized paddy soil was carried out. The rice root system affects CH 4 production and oxidation in the rice rhizosphere, and its influence varies with different rice cultivars. Rice cultivars with few unproductive tillers, a small root system, high root oxidative activity, and high harvest index are ideal for mitigating CH 4 emission in paddy fields.Key words: methane emission, methanogenic archaeon, methanotrophic bacterium, rice cultivar, subtropical paddy field Methane is one of the significant greenhouse gases related to global warming, and its concentration in the global atmosphere is increasing at a rate of approximately 1% per year 11,35) . In lowland rice cultivation, rice plants grow under flooded conditions and CH 4 is emitted from the fields. Controlling CH4 emission from the paddy fields contributes to the mitigation of global warming. Figure 1 57) shows a sketch of a flooded rice field in relation to CH 4 production, oxidation, and emission, along with CH4 diffusion, ebullition, and leaching from the paddy soil. Rice plants play the key role in CH 4 emission from paddy fields: (1) they supply root exudate and detritus which are substrates for CH4 production 56) ; (2) the rice aerenchyma system is a major pathway of CH 4 from paddy soil to atmosphere 13,42,46) ; (3) the aerenchyma system is also a pathway of O 2 supply to the rice rhizosphere by downward transportation, thus rice plants support CH4 oxidation in the rhizosphere; and (4) the rice rhizosphere itself is an important niche for methanotrophic bacteria which oxidize CH 4 to CO 2 56,63) . Methanogenic archaea (methanogens) are strictly anaerobic microbes belonging to the Archaea domain, and play an important role in anoxic environments by performing the last step of the anaerobic decomposition of organic matter: mineralization into CH 4 and CO 2 27) . Information on the genera and species of methanogenic archaea occurring in flooded paddy soils is gradually accumulating, but it is still limited. On the other hand, methanotrophic bacteria are obligately aerobic respiratory bacteria that can utilize CH 4 as their sole carbon and e...

Enumeration of Chemoorganotrophic Carbonyl Sulfide (COS)-degrading Microorganisms by the Most Probable Number Method

“…The most probable number (MPN) method has been widely used to estimate the cell densities of the microorganisms involved in the carbon, nitrogen, and sulfur cycles (e.g. methanogenic/methanotrophic [Adachi, 2001], denitrifying [Braker et al, 2010], and sulfur-oxidizing microbes [Li et al, 2008]). However, difficulties are associated with quantifying biological COS degradation due to the chemical hydrolysis of COS (Elliott et al, 1989) by water in bacterial cultures.…”

Climate Change and Crops

“…Variations in CH 4 emission from paddy fields are attributable mostly to variations in methanotrophic activity (Schütz et al 1989), indicating that methanotrophs are suitable organisms for controlling CH 4 emission (Adachi 2001). Therefore, stimulation of the populations and/or activity of methanotrophs can decrease CH 4 emission.…”

Methane Emission from Paddy Fields and its Mitigation Options on a Field Scale

“…In terms of environmental factors, temperature 33,37,153) and water regime 92,110) principally determine the potential for CH4 emission. On the microbial and plant scales, the amount of CH4 emitted is determined by the population and activity of microorganisms 1,34,44,48,86) , the physical conditions and chemical properties of the soil 125,126,135,151,152) , the biomass and activity of rice plants 22,28) , and the kinds and amounts of substrates 68,137) .…”