School of Oceanography, Shanghai Jiao Tong University, Shanghai, China.
Department of Oceanography, School of Ocean and Earth Science and Technology (SOEST), University of Hawai'i at Mānoa, Honolulu, HI, USA.
ISME J. 2022 Jun;16(6):1557-1569. doi: 10.1038/s41396-022-01204-z. Epub 2022 Feb 10.
Small eukaryotic phytoplankton are major contributors to global primary production and marine biogeochemical cycles. Many taxa are thought to be mixotrophic, but quantitative studies of phagotrophy exist for very few. In addition, little is known about consumers of Prochlorococcus, the abundant cyanobacterium at the base of oligotrophic ocean food webs. Here we describe thirty-nine new phytoplankton isolates from the North Pacific Subtropical Gyre (Station ALOHA), all flagellates ~2-5 µm diameter, and we quantify their ability to graze Prochlorococcus. The mixotrophs are from diverse classes (dictyochophytes, haptophytes, chrysophytes, bolidophytes, a dinoflagellate, and a chlorarachniophyte), many from previously uncultured clades. Grazing ability varied substantially, with specific clearance rate (volume cleared per body volume) varying over ten-fold across isolates and six-fold across genera. Slower grazers tended to create more biovolume per prey biovolume consumed. Using qPCR we found that the haptophyte Chrysochromulina was most abundant among the isolated mixotrophs at Station ALOHA, with 76-250 cells mL across depths in the upper euphotic zone (5-100 m). Our results show that within a single ecosystem the phototrophs that ingest bacteria come from many branches of the eukaryotic tree, and are functionally diverse, indicating a broad range of strategies along the spectrum from phototrophy to phagotrophy.
小型真核浮游植物是全球初级生产力和海洋生物地球化学循环的主要贡献者。许多类群被认为是混合营养的，但只有极少数类群进行过吞噬作用的定量研究。此外，关于贫营养海洋食物网底层的丰度很高的蓝细菌——聚球藻的消费者知之甚少。在这里，我们描述了来自北太平洋亚热带环流（ALOHA 站）的 39 种新的浮游植物分离株，它们都是鞭毛藻，直径约 2-5 μm，我们定量研究了它们吞噬聚球藻的能力。这些混合营养体来自不同的类群（双鞭毛藻、甲藻、金藻、腰鞭毛藻、一个鞭毛藻类和一个绿藻），其中许多来自以前未培养的进化枝。摄食能力差异很大，特定清除率（每体积清除的体积）在分离株之间变化超过 10 倍，在属之间变化超过 6 倍。摄食速度较慢的浮游生物往往会在消耗每单位猎物生物量时产生更多的生物量。通过 qPCR 我们发现，在 ALOHA 站的分离混合营养体中，甲藻 Chysochromulina 最为丰富，在上层真光层（5-100 m）的不同深度存在 76-250 个细胞 mL。我们的研究结果表明，在单一生态系统中，吞噬细菌的光合生物来自真核生物树的许多分支，并且具有功能多样性，这表明在从光营养到吞噬营养的光谱上存在广泛的策略。
