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Front. Microbiol. | doi: 10.3389/fmicb.2018.02289

Insight into the pico- and nano-phytoplankton communities in the deepest biosphere, the Mariana Trench

  • 1Key Laboratory of Biofuels, Shandong Provincial Key Laboratory of Energy Genetics, Qingdao Institute of Bioenergy and Bioprocess Technology, Qingdao Institute of Bioenergy and Bioprocess Technology (CAS), China
  • 2Physical Oceanography Laboratory/Qingdao Collaborative Innovation Center of Marine Science and Technology, Key Laboratory of Marine Chemistry Theory & Engineering,, Ocean University of China, China
  • 3Department of Ocean Science &Engineering, Southern University of Science and Technology, China

As photoautotrophs, phytoplankton are generally present in the euphotic zone of the ocean, however, recently healthy phytoplankton cells were found to be also ubiquitous in the dark deep sea, i.e., at water depths between 2000 and 4000 m. However, the distributions of phytoplankton communities in much deeper waters, such as the hadal zone, are unclear. In this study, the vertical distribution of the pico- and nano-phytoplankton (PN) communities from the surface to 8320 m, including the epipelagic, mesopelagic, bathypelagic, and hadal zones, were investigated via both 18S rRNA and p23S rRNA gene analysis in the Challenger Deep of the Mariana Trench. The results showed that Dinoflagellata, Chrysophyceae, Haptophyta, Chlorophyta, Prochloraceae, Pseudanabaenaceae, Synechococcaceae and Eustigmatophyceae, etc., were the predominant PN in the Mariana Trench. Redundancy analyses revealed that depth, followed by temperature, was the most important environmental factors correlated with vertical distribution of PN community. In the hadal zone, the PN community structure was considerably different from those in the shallower zones. Some PN communities, e.g. Eustigmatophyceae and Chrysophyceae, which have the heterotrophic characteristics, were sparse in shallower waters, while they were identified with high relative abundance (94.1% and 20.1%, respectively) at the depth of 8320 m. However, the dinoflagellates and Prochloraceae Prochlorococcus were detected throughout the entire water column. We proposed that vertical sinking, heterotrophic metabolism, and/or the transition to resting stage of phytoplankton might contribute to the presence of phytoplankton in the hadal zone. This study provided insight into the PN community in the Mariana Trench, and implied the significance of phytoplankton in exporting organic matters from the euphotic to the hadal zone, and also hinted the possible existence of some undetermined energy metabolism (e.g. heterotrophy) of phytoplankton making themselves adapt and survive in the hadal environment.

Keywords: Pico- and nano-phytoplankton, 18S rRNA, Plastid 23S rRNA, Mariana trench, deep sea

Received: 31 May 2018; Accepted: 07 Sep 2018.

Edited by:

Senjie Lin, University of Connecticut, United States

Reviewed by:

Rui Zhang, Xiamen University, China
Yonghong Bi, Institute of Hydrobiology, Chinese Academy of Sciences, China  

Copyright: © 2018 Guo, Liang, Xin, Wang, Cao, Xie, Zhang, Tian and Zhang. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Dr. Jiwei Tian, Ocean University of China, Physical Oceanography Laboratory/Qingdao Collaborative Innovation Center of Marine Science and Technology, Key Laboratory of Marine Chemistry Theory & Engineering,, Qingdao, China, tianjw@ouc.edu.cn
Dr. Yongyu Zhang, Qingdao Institute of Bioenergy and Bioprocess Technology (CAS), Key Laboratory of Biofuels, Shandong Provincial Key Laboratory of Energy Genetics, Qingdao Institute of Bioenergy and Bioprocess Technology, Qingdao, China, zhangyy@qibebt.ac.cn