2026-05-27 国立遺伝学研究所
図：草津温泉に生息するイデユコゴメ類と低温・高温環境での様子
（A）草津温泉において、高温条件下で活発に増殖しているイデユコゴメ類マット（左）と、低温条件下で増殖がほとんど停止しているマット（右）。低温期には水流によってマットが減少するものの、岩の隙間などにイデユコゴメ類が生存していることを示す顕微鏡写真を右パネル内に示す。
（B）イデユコゴメ類の生息環境調査を行う大学院生の辻野さん。
（C）培養温度ごとの顕微鏡写真。低温（20°C）でも適温（40°C）でも、細胞の形態や色はほとんど変化しない。
＜関連情報＞
自然生息地由来のゲノムが簡略化された紅藻類シアニディオ藻類における温度依存性の光安定性と窒素制限 Temperature-dependent photostasis and nitrogen limitation in streamlined-genome red algae Cyanidiophyceae from natural habitats
Dai Tsujino,Takayuki Fujiwara,Shota Yamashita,Kei Tamashiro,Jin Izumi,Fumi Yagisawa,Baifeng Zhou,Shunsuke Hirooka,Yuki Sunada,Kintake Sonoike,…
The ISME Journal Published:30 April 2026
DOI:https://doi.org/10.1093/ismejo/wrag105
Abstract
Photosynthetic microorganisms must continuously balance light energy absorption with metabolic demand to maintain photostasis under fluctuating environments. Cyanidiophyceae, unicellular red algae from acidic hot springs with highly streamlined genomes (9–18 Mb), nevertheless thrive across a wide temperature range (20°C–56°C), posing the question of how such minimalist eukaryotic cells sustain photostasis in nature. Here, we combined field observations of natural mats in sulfuric hot springs in Japan with laboratory experiments under habitat-mimicking conditions. Spring-water chemistry remained nearly constant year-round, characterized by low nitrogen availability (<30 μM), whereas temperature varied spatially and seasonally. Growth increased with temperature (up to 47°C) and nearly ceased at 20°C–25°C, yet photosynthetic pigment levels and apparatus components remained largely unchanged, indicating sustained light absorption even under conditions of minimal growth. At low temperatures, photosystem efficiency and regulated energy dissipation decreased, whereas nonregulated dissipation and reactive oxygen species (ROS) increased, indicating excess excitation energy was mainly dissipated through nonregulated pathways. Proteomic and transcriptomic analyses showed accumulation of ROS scavengers and chromosome maintenance/repair proteins at low temperature, suggesting that excess reducing power/adenosine triphosphate (ATP), even after partial energy dissipation, was redirected toward stress mitigation rather than growth. At higher temperatures, nitrogen-deficiency responses emerged, reflecting nitrogen limitation relative to elevated demand for rapid growth. Together, these results reveal a temperature-dependent trade-off in Cyanidiophyceae in natural habitats: oxidative stress at low temperature versus nitrogen limitation at high temperature. Overall, our findings highlight a simple yet robust photostasis strategy and provide environmental and omics resources for studies of this model lineage.
