2026-10-27 九州大学
ミズワタクチビルケイソウが繁茂した河床の様子と環境DNA検出イメージ（写真:フィッシングジャーナリスト佐藤成史、DNA検出イメージ: 生成AI作成）
＜関連情報＞
- https://www.kyushu-u.ac.jp/ja/notices/view/3201
- https://www.sciencedirect.com/science/article/pii/S2772735125001702
- https://link.springer.com/article/10.1007/s10201-024-00751-y
環境DNAを用いた侵入性珪藻Cymbella janischiiの検出アッセイの改良と分布解析 Detection assay improvements and distribution analyses of the invasive diatom Cymbella janischii from environmental DNA
Yoko Kato-Unoki,Tamie Suzawa,Trang Tran Thu,Takumi Sugahara, Yasuhiro Mitani,Yoshitsugu Masuda,Jun-ichi Tsuboi, Toshifumi Minamoto,Satoquo Seino
Water Biology and Security Available online: 27 November 2025
DOI:https://doi.org/10.1016/j.watbs.2025.100527
Highlights
•Improved Cymbella janischii-specific detection assay from river water eDNA.
•Water eDNA detection showed a positive correlation with microscopic results.
•Benthic eDNA can be used to assess invasion history and bloom-prone streams.
•Distribution analysis showed contrasting bloom behaviors in the two river systems.
•This assay will aid the management and associated further studies of C. janischii.
Abstract
Recently, invasive species have become a major concern, and countermeasures are now part of the United Nations Sustainable Development Goals. Environmental DNA (eDNA) analysis, which enables high-sensitivity detection of target species simply by collecting water, is a powerful tool for monitoring and managing invasive species across broad survey areas. In a previous study, we developed specific detection assays for Cymbella janischii (A. Schmidt) De Toni 1891—an invasive diatom that has recently invaded Japan and caused freshwater problems—from benthic eDNA. However, these assays were sometimes difficult to apply to river water samples with admixture DNA and low-target DNA. Here, we enhanced an existing assay, validated its detection accuracy from water eDNA through microscopic observation and benthic eDNA, and used it to analyze the diatom distribution in the Kase and Chikugo river systems, Japan. The assay was improved using a probe in the P1 primer set, and its specificity against the DNA of related species was confirmed. The quantification results of water eDNA showed positive correlations (r = 0.62, p = 0.002, n = 22) with the prevalence of microscopic observations, similar to those of benthic eDNA (r = 0.80, p < 0.001, n = 22). However, the results of detection agreement analysis revealed discordance rates of 0.222 and 0.154 (95 % CIs: 0.028–0.600 and 0.019–0.454, respectively) for the positive and negative classes, respectively, and indicated that the detection results may be unstable when the biomass is very low. From monitoring and distribution analyses, we found that this species was less likely to form colonies even after invasion in the Kase River, whereas it repeatedly bloomed in the Chikugo River under optimal conditions for the species, even having previously disappeared. The presence, absence, and distribution characteristics obtained from this assay will help in understanding the ecology, physiology, ecological impacts, and bloom factors of C. janischii, contributing to the formulation of strategies for its management and countermeasures.
日本における侵入性珪藻Cymbella janischiiの環境DNAからの特異的検出アッセイの開発 Development of specific detection assays from environmental DNA of invasive diatom Cymbella janischii in Japan
Yoko Kato-Unoki, Shigeki Mayama, Akira Kurihara & Toshifumi Minamoto
Limnology Published:15 May 2024
DOI:https://doi.org/10.1007/s10201-024-00751-y
Abstract
The effect of invasive species on existing biological systems has become a major concern in recent years. Countermeasures for invasive species were among the goals of the United Nations Biodiversity Conference (COP15). Cymbella janischii is an alien diatom that recently invaded Japan. Its algal blooms not only spoil the scenery of the river but also raise concerns about its impact on the ecosystem, including damage to fish populations. To monitor the invasion of this species and employ river management, we developed the specific detection assays for this species from environmental DNA, using a polymerase that distinguishes a single base difference at the 3′ end of the primer. Three assays for amplifying nuclear-encoded large-subunit rRNA genes (P1, P2, and P3) successfully detected C. janischii without false positives in benthic samples from 12 rivers in Japan. There were no significant differences among the results obtained using the three assays. The three assays showed significant positive correlations with the microscopic observation results, having the advantage of detecting species with low population density. These assays can be performed using inexpensive equipment because they do not necessarily require real-time PCR. However, it can enhance specificity by adding a fluorescent probe to the internal sequence, if necessary. These detection assays can apply to a wide range of environmental samples and are expected to help elucidate the invasive characteristics and ecology of this species.
