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January 13, 2021
Kanto Natural Gas Development Co., Ltd.

Ongoing biological methanogenesis by archaea in iodine-rich deep aquifer
around Mobara, southern Kanto region

1. Key points

Molecular-level analysis of coenzyme F430, a unique marker of methanogenic archaea, revealed that archaea living in deep aquifers of the southern Kanto region continue to produce methane even now.
The archaea community in the deep aquifer includes many different microorganisms with methanogenic archaea.
The input of modern carbon via rainwater or ambient seawater to the deep aquifer is not significant, suggesting an isolated deep biosphere which is independent from surface environment.

2. Overview

The corresponding authors Dr. Yoshinori Takano, deputy director of the Biogeochemistry Research Center of the Research Institute for Marine Resources Utilization of JAMSTEC (President: Tadashi Matsunaga) and Atsushi Urai, researcher at the Graduate School of Medicine, Science and Technology, Shinshu University (dean: Kunihiro Hamada) analyzed samples from the Minami Kanto gas field, located in the southern Kanto region (Figures 1&2), in collaboration with Kanto Natural Gas Development Co., Ltd. (CEO: Takeshi Mori) and the Atmosphere and Ocean Research Institute of the University of Tokyo. They found that archaea living in deep fluids are producing methane even now. They also confirmed the presence of a highly diverse microbial community in the deep habitat.

Researches in the recent years has rapidly improved our understanding on topics such as the limits of subseafloor biospheres (reported on July 24, 2015) and methane cycles involving benthic microorganisms (reported on September 24, 2018). Nevertheless, very little was known about the abundance and activity of archaea deep underground in the Kanto region where methane and iodine are produced.

The present study conducted molecular-level analysis on coenzyme F430 (*), which is unique to methanogenic archaea. The results showed that archaea continue to produce methane deep underground even now, forming a deep biosphere in an isolated environment with hardly any supply of carbon from the Earth’s surface (Figures 3&4).

These findings will hopefully further elucidate the ecology of highly diverse archaea communities and the processes of methanogenesis in the iodine-rich deep aquifer.

This study represents joint research between JAMSTEC and Kanto Natural Gas Development Co., Ltd. These results were published in the January 8th, 2021 (Japan time) issue of ACS Earth and Space Chemistry, a specialized academic journal published by the American Chemical Society.

Origin of Deep Methane Associated with a Unique Community of Microorganisms in an Organic- and Iodine-Rich Aquifer
Atsushi Urai1,2, Yoshinori Takano1, Hiroyuki Imachi1, Shunichi Ishii1, Yohei Matsui1,3, Miyuki Ogawara1, Eiji Tasumi1, Yosuke Miyairi3, Nanako O. Ogawa1, Toshihiro Yoshimura1, Fumio Inagaki1, Yusuke Yokoyama1,3, Kenjiro Kawano4, Daisuke Murai4, Park Ho-Dong2, Naohiko Ohkouchi1
2. Shinshu University
3. Atmosphere and Ocean Research Institute, The University of Tokyo
4. Kanto Natural Gas Development Co., Ltd.

【Supplemental information】

Coenzyme F430 is a chemical compound uniquely related to methanogenic archaea and anaerobic methane-oxidizing archaea (ANME). Different species of methanogenic archaea use different substrates (precursors) to produce methane. However, all methanogenic archaea have F430, as F430 is involved in the final catalytic reaction of all methanogenic pathways. It is therefore possible to estimate the total abundance of methanogenic archaea by measuring the concentration of F430. The presence of F430 suggests that ongoing archaeal methanogenesis occurs in the environment.

Figure 1. The location of Mobara city, Chiba prefecture and the Minami Kanto gas field (orange).


Figure 2. (Left) An outlet of a deep-seated aquifer. The photo shows foam covering the water surface of the outlet after a strong gush. It became clear that this foam was derived from the microbial life, seated deeply underground. Thus, this outlet could be regarded as a “window” to the underground biosphere that spreads in the deep-seated aquifer. (Right) Gas was collected by water displacement. Analysis of the collected gas indicated highly pure methane (purity >99 %). The water is yellowish because the aquifer has a high concentration of iodine and dissolved organic matter. There is a large amount of foam between the gas phase and the liquid phase.


Figure 3. Chemical structure of coenzyme F430 and a chromatogram of F430 detected in the deep aquifer. The present study successfully detected a high concentration level of F430 in a sample collected from the gas well. F430 is known to quickly isomerize (epimerize) after being released from the cell. However, no epimer of F430 was detected in the deep-seated aquifer at the survey location.


Figure 4. Two-dimensional plot of methane and dissolved inorganic carbon, constructed by radiocarbon isotope ratio (Δ14C) and stable carbon isotope ratio (δ13C). Hardly any radiocarbon was found in the methane and the dissolved inorganic carbon from the deep aquifer, indicating that the carbon cycle was isolated from the atmosphere-derived carbon (the blue area).


(For this study)
Yoshinori Takano, deputy director, Biogeochemistry Research Center (BGC), Research Institute for Marine Resources Utilization (MRU), JAMSTEC
(For press release)
Public Relations Section, Marine Science and Technology Strategy Department, JAMSTEC
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