第6回極域科学シンポジウム分野横断セッション：[IB2] 地球環境変動の解析と地球生命システム学の構築11月19日（木）　統計数理研究所 セミナー室1（D305

Abe Takashi

Baba Tomoya

Kagoshima Hiroshi

Naganuma Takeshi

Nakai Ryosuke

Niki Hironori

Satoshi Imura

Yanagihara Katsuhiko

National Institute of Polar Research Repository

  Bryosphere within an Antarctic moss pillar  Ryosuke Nakai1, 2, Tomoya Baba3, Katsuhiko Yanagihara3, Hiroshi Kagoshima3, Takashi Abe4, Takeshi Naganuma5, Satoshi Imura6, Hironori Niki1 1 National Institute of Genetics 2Research Fellow of the Japan Society for the Promotion of Science 3Transdisciplinary Research Integration Center 4Graduate School of Science and Technology, Niigata University 5Graduate School of Biosphere Science, Hiroshima University 6National Institute of Polar Research  The aquatic moss, Leptobryum wilsonii, forms underwater tower-like structures called “moss pillars” (Koke Bouzu, in Japanese) in ultra-oligotrophic Antarctic lakes. These pillars comprise distinct redox-affected sections, that is, oxidative exteriors and reductive interiors. Our objective here was to understand how such a unique ecosystem survives in such extreme environments. Using biochemical and molecular methods, we studied the microbiome of aquatic moss pillars, based on the fatty acid profile, rDNA genotyping, and metagenomic information. Our results indicated that the bacterial communities differed among the exterior, upper-interior, and lower-interior sections, and that more than 60% of the obtained 16S rDNA phylotypes were of a novel taxa at the species, genera, or class levels. Furthermore, a wide range of eukaryotic 18S rDNA phylotypes related to algae, ciliates, fungi, nematodes, rotifers, and tardigrades were present in the pillar. In parallel, we analyzed the diversity of functional genes encoding the CO2-fixing enzyme RuBisCO, nitrogenase (nifH), nitrite reductase (nirK and nirS), and nitric oxide reductase (qnorB), all of which are involved in carbon and nitrogen cycling in a pillar. Phylogenetic analyses revealed that cyanobacterial RuBisCO genotypes were found exclusively in the pillar exterior; however, genotypes related to chemoautotrophic bacteria were detected in the lower-interior of the pillar. Furthermore, γ-proteobacterial nifH showed pillar-wide distribution, while cyanobacterial nifH sequences were specific to the exterior, and sulfate-reducing δ-proteobacterial nifH sequences were subdominant in the interior. Such microbial functional zonation, as reflected by the redox gradient in a pillar, was also identified during analyses of other gene sequences. These findings will shed light on the mechanisms underlying the maintenance of the “bryosphere” within these pillars.              Figure 1. Antarctic moss pillars found in Lake Hotoke-Ike.  References Imura S, Bando T, Saito S, Seto K, Kanda H (1999) Benthic moss pillars in Antarctic lakes. Polar Biology, 22, 137–140. Nakai R, Abe T, Baba T, Imura S, Kagoshima H, Kanda H, Kanekiyo A, Kohara Y, Koi A, Nakamura K, Narita T, Niki H, Yanagihara K, Naganuma T (2012) Microflorae of aquatic moss pillars in a freshwater lake, East Antarctica, based on fatty acid and 16S rRNA gene analyses. Polar Biology, 35, 425–433. Nakai R, Abe T, Baba T, Imura S, Kagoshima H, Kanda H, Kohara Y, Koi A, Niki H, Yanagihara K, Naganuma T (2012) Eukaryotic phylotypes in aquatic moss pillars inhabiting a freshwater lake in East Antarctica, based on 18S rRNA gene analysis. Polar Biology, 35, 1495–1504. Nakai R, Abe T, Baba T, Imura S, Kagoshima H, Kanda H, Kohara Y, Koi A, Niki H, Yanagihara K, Naganuma T (2012) Diversity of RuBisCO gene responsible for CO2 fixation in an Antarctic moss pillar. Polar Biology, 35, 1641–1650. 

Bryosphere within an Antarctic moss pillar

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Bryosphere within an Antarctic moss pillar

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