Vertical Distribution of Microbial Eukaryotes From Surface to the Hadal Zone of the Mariana Trench

Abstract

Marine microbial eukaryotes are ubiquitous, comprised of phylogenetically diverse groups and play key roles in microbial food webs and global biogeochemical cycling. However, their vertical distribution in the deep sea has received little attention. In this study, we investigated the composition and diversity of the eukaryotes of both 0.2–3 μm and >3 μm size fractions from the surface to the hadal zone (8727 m) of the Mariana Trench using Illumina MiSeq sequencing for the 18S rDNA. The microbial eukaryotic community structure differed substantially across size fractions and depths. Operational taxonomic unit (OTU) richness in the >3 μm fraction was higher than that in the 0.2–3 μm fraction at the same depth. For the 0.2–3 μm fraction, sequences of Retaria (Rhizaria) were most abundant in the surface water (53.5%). Chrysophyceae (Stramenopiles) sequences dominated mostly in the samples from water depths below 1795 m. For the >3 μm fraction, sequences of Dinophyceae (Alveolata) were most abundant in surface waters (49.3%) and remained a significant proportion of total sequences at greater depths (9.8%, on average). Retaria sequences were abundant in samples of depths ≥1000 m. Amoebozoa and Apusozoa sequences were enriched in the hadal sample, comprising 38 and 20.4% of total sequences, respectively. Fungi (Opisthokonta) sequences were most abundant at 1759 m in both size fractions. Strong positive associations were found between Syndiniales (mainly MALV-I and MALV-II) and Retaria while negative associations were shown between MALV-II and Fungi in a co-occurrence analysis. This study compared the community structure of microbial eukaryotes in different zones in the deep sea and identified a distinct hadal community in the larger size fraction, suggesting the uniqueness of the eukaryotes in the biosphere in the Mariana Trench.

Marked changes in diversity and relative activity of picoeukaryotes with depth in the world ocean

“…A global survey indicated that the distribution of protists in the upper ocean is predominantly structured by oceanographic basin, pointing to dispersal limitation [4,5], while in the bathypelagic layer, protist assemblages appear to be structured by water masses [6]. Previous studies on the distribution of protists along the water column are limited to a few specific oceanic regions and indicate a clear differentiation between epipelagic and deep ocean communities [7][8][9][10][11][12][13][14].…”

Fungal community analysis in seawater of the Mariana Trench as estimated by Illumina HiSeq

“…19 Due to the special ecological environments around the trench, it may contain abundant fungal resources. In the last decades, there were several studies on the diversity of microbes including actinomycetes, 20 bacteria, fungi and Picoeukaryotic isolated from sediments and seawaters in the Pacic Ocean and Mariana Trench 8,11,14,[20][21][22] by culture and molecular approches.…”

Fungal communities in sediments along a depth gradient in the Eastern Tropical Pacific

“…Fungi are active members of deep-sea sediment communities (Pachiadaki et al, 2016; Morales et al, 2019), but in this ecosystem, they are far more poorly characterized than bacteria and archaea (Edgcomb et al, 2011; Nagano and Nagahama, 2012; Dekas et al, 2016; Xu et al, 2018). In deep waters, fungi are well adapted to the total absence of light, low temperatures, and high hydrostatic pressure.…”

“…In recent years, there has been a growing interest in studying fungal communities in deep-sea environments using culture-dependent and, to an increasing extent, culture-independent methods. Abundant fungal populations have been observed in a variety of deep-sea locations such as asphalt seeps in Sao Paulo Plateau (Nagano et al, 2017), methane seeps in the Kuroshima Knoll (Takishita et al, 2006), hydrothermal vents in the Mid-Atlantic Ridge (Le Calvez et al, 2009; Xu et al, 2017), sediments of the Peru Trench (Edgcomb et al, 2011), the East Indian Ocean (Zhang et al, 2014), the High Arctic (Zhang et al, 2015), the Mariana Trench (Xu et al, 2016, 2018), the Yellow Sea (Li et al, 2016), the Mediterranean Sea (Barone et al, 2018), the Yap Trench (Li et al, 2019), and subsurface sediments in Suruga-Bay (Nagano et al, 2016).…”