海洋環境DNAを用いた黒潮域における微生物群集の解明～微生物の群集構造や分布パターンから探る生態系構造～

2025-11-28 東京大学

東京大学らの研究チームは、黒潮域の海水から得た環境DNAをメタバーコーディング解析し、原核生物と真核微生物の群集構造と分布パターンを同時に評価した。白鳳丸・新青丸の航海で採取した表層(10–150m)の試料を解析した結果、原核生物群集は主に水温・クロロフィルaなど物理環境や植物プランクトン由来の物質により変動し、季節・深度で構造が大きく変化することが示された。一方、真核微生物群集は環境要因で説明されにくく、生物間相互作用(寄生・補食など)が群集形成の主因と考えられた。また、原核生物と多くの渦鞭毛藻類は似た分布を示す一方、ウミタル類など従属栄養性の真核微生物は局所的にブルームを形成し、微生物食物網を変化させる可能性が示唆された。本研究は、微生物群集が担う黒潮生態系の基盤構造や機能解明に貢献し、漁業生産にも重要な知見となる。

調査海域と本研究のイメージ

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亜熱帯黒潮域における海洋原核生物および真核生物群集の異なる構造因子と分布パターン

Different structuring factors and distribution patterns of marine prokaryotic and eukaryotic communities in the subtropical Kuroshio region

Youta Sugai,Masayuki Ushio,Junya Hirai,Masumi Hasegawa-Takano,Takayoshi Fujiwara,Mako Takada,Kaho Mori,Hideki Fukuda,Hiroaki Saito,Koji Hamasaki,Susumu Hyodo,Susumu Yoshizawa

Frontiers in Marine Science Published:28 November 2025

DOI:https://doi.org/10.3389/fmars.2025.1656531

To clarify the differences in the effect of environments on community structures and in distribution patterns between marine prokaryotes and microbial eukaryotes, microbial communities were investigated spatially and seasonally in the surface layer of the subtropical Kuroshio region using environmental DNA (eDNA) metabarcoding analysis. Prokaryotic communities were primarily different between seasons and dominated by Flavobacteriales (33.4 ± 11.6%) and Synechococcales (25.0 ± 21.2%) during spring and autumn, respectively. For eukaryotes, diverse dinoflagellates including Syndiniales were frequently dominant (46.7 ± 8.2%) regardless of seasons, and the horizontally and vertically collected eDNA samples successfully captured the spatially heterogeneous dominance of Copelata (34.3–36.4%) and Doliolida (60.3–67.3%) at shallower depths (10–50 m) and Spumellaria (39.4–94.9%) at deeper depths (100–150 m). A large proportion (64.6%) of the variance in the community structure of prokaryotes was explained by physical conditions and chlorophyll (chl.) a concentration, which indicates that the physical environments of water masses and resource supply by phytoplankton mainly shape prokaryotic communities. On the other hand, the effect of physical conditions on community structure was much smaller for eukaryotes (10.7%) compared to prokaryotes (29.6%), and the variance was most (24.7%) explained by chl. a concentration but largely (64.6%) unexplained. This result suggests that food environments and other factors including parasitic interactions determine eukaryotic communities rather than physical conditions. The communities of prokaryotes and some eukaryotes such as Dinophyceae and Spirotrichea showed relatively similar spatio-temporal distributions probably due to their symbiotic and trophic interactions and were detected commonly. In contrast, the distinct and unique distributions of other heterotrophic eukaryotes such as Doliolida were observed, indicating their sporadic and massive blooms in favorable environments for each community. The comparison of these distribution patterns across taxonomic and trophic levels implicates the ecological roles of microbial communities in maintaining the stable structure and functions of marine ecosystems and changing the structure of the microbial food web locally.