Shift and Metabolic Potentials of Microbial Eukaryotic Communities Across the Full Depths of the Mariana Trench.

Xiao-Yu Zhu,Jiwen Liu,Chun-Xu Xue,Xiao-Hua Zhang,Jiwei Tian

doi:10.3389/fmicb.2020.603692

Abstract

Microbial eukaryotes are widespread and play important roles in marine ecosystems. However, their ecological characteristics in the deep sea (>1,000 m), especially hadal trenches, were largely unknown. Here, we investigated the diversity and metabolic potentials of microbial eukaryotes along the whole water column of the Mariana Trench by metagenomics. Our results showed clear depth-related distribution of microbial eukaryotic community and associated metabolic potentials. Surface seawater was dominated by phototrophic/mixotrophic groups (e.g., Dinoflagellata) and genes involved in biosynthesis (photosynthesis and fatty acid biosynthesis), while deep (bathypelagic and/or hadal) seawaters were enriched with heterotrophic groups (e.g., Bicoecea) and genes related to digestion (lysosomal enzymes and V-type ATPase) and carbohydrate metabolism. Co-occurrence analysis revealed high intra-domain connectivity, indicating that microbial eukaryotic composition was more influenced by microbial eukaryotes themselves than bacteria. Increased abundance of genes associated with unsaturated fatty acid biosynthesis likely plays a role in resisting high hydrostatic pressure. Top1 and hupB genes, responsible for the formation and stabilization of DNA structure, were unique and abundant in the hadal zone and thus may be helpful to stabilize DNA structure in the deep sea. Overall, our results provide insights into the distribution and potential adaptability of microbial eukaryotes in the hadal zone.

Highlights

With high morphological and genetic variability, microbial eukaryotes fulfill a variety of crucial ecological roles and are essential participants of marine carbon cycle (Azaml et al, 1983; Worden et al, 2015)
Salinity was constant throughout the water column (34.0−34.8), while temperature and pH generally decreased from the surface (29◦C; 8.2) to the trench bottom (∼1◦C; 7.8) (Supplementary Figure 2)
This study investigated the distribution of microbial eukaryotes along the water column of the deepest known ocean

Summary

Introduction

With high morphological and genetic variability, microbial eukaryotes fulfill a variety of crucial ecological roles and are essential participants of marine carbon cycle (Azaml et al, 1983; Worden et al, 2015). Jing and Xu recently conducted the first survey of microbial eukaryotes dwelling in the hadal waters (depth up to 8,727 m) of the Mariana Trench (Jing et al, 2018; Xu et al, 2018). Alveolata dominated the surface waters whereas Stramenopiles were enriched in the deep waters Despite these information, little is known about the microbial eukaryotic communities and metabolic potentials in the deeper seawaters (8,727–11,000 m) of the Mariana Trench, where unique microbial populations (e.g., increased amount of SAR406, hydrocarbondegrading microbes) have been observed (Ichino et al, 2015; Nunoura et al, 2015; Liu et al, 2018, 2019b; Gao et al, 2019). Knowledge of microbial eukaryotes at the bottom of the Mariana Trench, the deepest ocean part on Earth, is necessary for a better understanding of their ecological roles and potential adaptability

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Conclusion