Graduate School of Natural Science, Konan University, Okamoto, Higashinada, Kobe, Hyogo, Japan.
Institute for Integrative Neurobiology, Konan University, Okamoto, Higashinada, Kobe, Hyogo, Japan.
PLoS One. 2019 Jan 9;14(1):e0208941. doi: 10.1371/journal.pone.0208941. eCollection 2019.
Labyrinthuleans (Labyrinthulea, Stramenopiles) are recognized as decomposers in marine ecosystems but their nutrient sources are not fully understood. We conducted two-membered culture experiments with labyrinthuleans and diatoms to discover where labyrinthuleans obtain their nutrients from. The results showed that Aplanochytrium strains obtained nutrients by consuming living diatoms. Aplanochytrium cells did not release digestive enzymes into the medium, but adhered to diatom cells via the tip of their characteristic ectoplasmic net system to obtain nutrients from them. The chloroplast and cell contents of the diatoms shrank and were absorbed, and then the number of Aplanochytrium cells rapidly increased as multiple aplanospores were released. To estimate the effect of labyrinthulean organisms including Aplanochytrium on marine ecosystem, we explored the dataset generated by the Tara Oceans Project from a wide range of oceanic regions. The average proportion of all labyrinthulean sequences to diatom sequences at each station was about 10%, and labyrinthulids, oblongichytrids, and aplanochytrids were the major constituent genera, accounting for more than 80% of labyrinthuleans. Therefore, these groups are suggested to greatly affect the marine ecosystem. There were positive correlations between aplanochytrids and phototrophs, green algae, and diatoms. At many stations, relatively large proportions of aplanochytrid sequences were detected in the size fraction larger than their cell size. This implied that Aplanochytrium cells increased their particle size by adhering to each other and forming aggregates with diatoms that are captured by larger zooplankton in the environment, thereby bypassing the food web pathway via aplanochytrids to higher predators. The intake of nutrients from diatoms by aplanochytrids represents a newly recognized pathway in the grazing food chain in the marine ecosystem.
片体虫（Labyrinthulea，Stramenopiles）被认为是海洋生态系统中的分解者，但它们的营养来源尚未完全了解。我们进行了双培养实验，研究片体虫和硅藻之间的相互关系，以探究片体虫的营养来源。结果表明，Aplanochytrium 菌株通过消耗活的硅藻来获取营养。Aplanochytrium 细胞不会向培养基中释放消化酶，而是通过其特有的胞外网系统的尖端黏附在硅藻细胞上，从它们那里获取营养。硅藻的叶绿体和细胞内容物收缩并被吸收，然后随着多个游动孢子的释放，Aplanochytrium 细胞的数量迅速增加。为了评估包括 Aplanochytrium 在内的片体虫类生物对海洋生态系统的影响，我们利用 Tara Oceans 项目在广泛的海洋区域生成的数据集进行了探索。每个站位的所有片体虫序列与硅藻序列的平均比例约为 10%，片体虫目、长形粘菌目和片体虫目是主要的组成属，占片体虫类的 80%以上。因此，这些类群可能对海洋生态系统产生重大影响。在许多站位，aplanochytrids 与光养生物、绿藻和硅藻之间存在正相关关系。在许多站位，检测到大于其细胞大小的粒径中存在相对较大比例的 aplanochytrid 序列。这意味着 Aplanochytrium 细胞通过彼此黏附并与被环境中较大的浮游动物捕获的硅藻形成聚集体来增加其颗粒大小，从而通过 aplanochytrids 绕过食物网途径到达更高的捕食者。aplanochytrids 从硅藻中摄取营养代表了海洋生态系统中摄食食物链中的一条新的被认可的途径。
