09:05 〜 09:30
[BCG05-01] Tree trunks in a mountain forest harbor methanogenic archaea and methane-oxidizing bacteria
★Invited Papers
キーワード：メタン生成古細菌、メタン酸化細菌、森林
Wetwood of living trees, which contains water-soaked xylem tissues and sometimes shows rotten symptoms, was demonstrated as a habitat of methanogenic archaea in the 1970s. However, the related studies have almost ceased for more than 40 years. Recently, tree trunks in upland forests have been recognized as a potential source of methane emission, and methanogenic archaea living inside trees have again been spotlighted. Here, we investigated methanogenic archaeal communities living inside trees in a mountain forest in Japan. Furthermore, methane-oxidizing bacteria, another key player in the forest methane dynamics, were isolated from the inside of the tree trunks for the first time.
Wood core segments of heartwood and sapwood were obtained with an increment borer from the trunk of seven tree species, Cryptomeria japonica (Cj, Sugi), Quercus crispula (Qc, Mizunara), Fraxinus mandchurica (Fm, Yachidamo), Acer pictum (Ap, Itayakaede), Aesculus turbinata (At, Tochinoki), Magnolia obovata (Mo, Hoonoki), and Populus tremula var. sieboldii (Pt, Yamanarashi) in the Ashiu Experimental Forest of Kyoto University in July 2020 and September 2021. The community structure of methanogenic archaea in the samples was investigated by real-time PCR and digital PCR analyses of methanogenic archaeal mcrA genes and amplicon sequencing analysis of 16S rRNA genes. The number of viable methanogenic archaea living inside the trees was also enumerated by a culture-dependent most-probable number (MPN) method with H2/CO2 as a substrate for methanogenesis. Methane-oxidizing bacteria were enriched in a nitrate liquid mineral-salt medium under ca. 12% (v/v) methane atmosphere conditions and isolated as pure culture strains.
The mcrA gene was detected from all the tree species, and some heartwood samples of Cj, Qc, Fm, and At contained more than 106 copies of mcrA g-1 dry wood. The MPN enumeration also demonstrated the inhabitation of viable methanogenic archaea inside the trees with a maximum of 106 cells g-1 dry wood, and methanogenic archaea related to Methanobacterium beijingensis were grown from the highest dilution tubes of the heartwood samples of Fm and Qc. The amplicon sequencing analysis showed that methanogenic archaea affiliated with Methanobacteriaceae and Methanomassiliicoccaceae mainly inhabited the tree trunks. Meanwhile, methane-oxidizing activities were observed from a sapwood sample of Ap and a heartwood sample of Cj, from which two novel methane-oxidizing bacterial strains related to Methylosinus spp. were isolated.
These results suggested that the inside of upland trees is a common habitat for methanogenic archaea and methane-oxidizing bacteria. Their distributions, community dynamics, and activities have the potentials to affect the methane budget in the forest ecosystem.
Wood core segments of heartwood and sapwood were obtained with an increment borer from the trunk of seven tree species, Cryptomeria japonica (Cj, Sugi), Quercus crispula (Qc, Mizunara), Fraxinus mandchurica (Fm, Yachidamo), Acer pictum (Ap, Itayakaede), Aesculus turbinata (At, Tochinoki), Magnolia obovata (Mo, Hoonoki), and Populus tremula var. sieboldii (Pt, Yamanarashi) in the Ashiu Experimental Forest of Kyoto University in July 2020 and September 2021. The community structure of methanogenic archaea in the samples was investigated by real-time PCR and digital PCR analyses of methanogenic archaeal mcrA genes and amplicon sequencing analysis of 16S rRNA genes. The number of viable methanogenic archaea living inside the trees was also enumerated by a culture-dependent most-probable number (MPN) method with H2/CO2 as a substrate for methanogenesis. Methane-oxidizing bacteria were enriched in a nitrate liquid mineral-salt medium under ca. 12% (v/v) methane atmosphere conditions and isolated as pure culture strains.
The mcrA gene was detected from all the tree species, and some heartwood samples of Cj, Qc, Fm, and At contained more than 106 copies of mcrA g-1 dry wood. The MPN enumeration also demonstrated the inhabitation of viable methanogenic archaea inside the trees with a maximum of 106 cells g-1 dry wood, and methanogenic archaea related to Methanobacterium beijingensis were grown from the highest dilution tubes of the heartwood samples of Fm and Qc. The amplicon sequencing analysis showed that methanogenic archaea affiliated with Methanobacteriaceae and Methanomassiliicoccaceae mainly inhabited the tree trunks. Meanwhile, methane-oxidizing activities were observed from a sapwood sample of Ap and a heartwood sample of Cj, from which two novel methane-oxidizing bacterial strains related to Methylosinus spp. were isolated.
These results suggested that the inside of upland trees is a common habitat for methanogenic archaea and methane-oxidizing bacteria. Their distributions, community dynamics, and activities have the potentials to affect the methane budget in the forest ecosystem.