Distribution and Niche Separation of Planktonic Microbial Communities in the Water Columns from the Surface to the Hadal Waters of the Japan Trench under the Eutrophic Ocean.

Takuro Nunoura,Yoshihiro Takaki,Hiroko Makita,Osamu Koide,Taichi Yokokawa,Shinsuke Kawagucci,Ken Takai,Junichi Miyazaki,Miho Hirai,Yukari Yoshida-Takashima,Manabu Nishizawa,Michinari Sunamura

doi:10.3389/fmicb.2016.01261

Takuro Nunoura, Yoshihiro Takaki + Show 10 more

Open Access

https://doi.org/10.3389/fmicb.2016.01261

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Abstract

The Japan Trench is located under the eutrophic Northwestern Pacific while the Mariana Trench that harbors the unique hadal planktonic biosphere is located under the oligotrophic Pacific. Water samples from the sea surface to just above the seafloor at a total of 11 stations including a trench axis station, were investigated several months after the Tohoku Earthquake in March 2011. High turbidity zones in deep waters were observed at most of the sampling stations. The small subunit (SSU) rRNA gene community structures in the hadal waters (water depths below 6000 m) at the trench axis station were distinct from those in the overlying meso-, bathy and abyssopelagic waters (water depths between 200 and 1000 m, 1000 and 4000 m, and 4000 and 6000 m, respectively), although the SSU rRNA gene sequences suggested that potential heterotrophic bacteria dominated in all of the waters. Potential niche separation of nitrifiers, including ammonia-oxidizing archaea (AOA), was revealed by quantitative PCR analyses. It seems likely that Nitrosopumilus-like AOAs respond to a high flux of electron donors and dominate in several zones of water columns including shallow and very deep waters. This study highlights the effects of suspended organic matter, as induced by seafloor deformation, on microbial communities in deep waters and confirm the occurrence of the distinctive hadal biosphere in global trench environments hypothesized in the previous study.

Highlights

Hadal oceans at water depths of below 6000 m are composed almost exclusively of trenches and are one of the least-explored biospheres on Earth
The predominance of potential heterotrophic populations represented by Bacteroidetes and “Ca. Marinimicrobia” (SAR406) in the small subunit (SSU) rRNA gene communities was observed from the sea surface to hadal waters in the Japan Trench region (Figure 3), whereas the potential chemolithotrophic populations; SAR324 and MGI Thaumarchaeota, dominate the microbial communities in mesopelagic to abyssal waters in the Mariana Trench (Nunoura et al, 2015)
The predominance of group α MGI in the shallow waters above 500 mbs detected was found in the Japan Trench but not in the Mariana Trench (Figure 5; Supplementary Figure S6)

Summary

Introduction

Hadal oceans at water depths of below 6000 m are composed almost exclusively of trenches and are one of the least-explored biospheres on Earth. The hadal biosphere and biogeochemical cycles are likely constrained primarily by the trench geomorphology and by the endogenous recycling and input of organic matter associated with occasional seafloor deformation (landslides and turbulent sediments) in the vast trench slope area (Glud et al, 2013; Ichino et al, 2015; Nunoura et al, 2015) Such a distinctive hadal microbial ecosystem has been found only in the Mariana Trench, and the following points should be addressed further: whether the distinctive hadal microbial ecosystem is widespread in the global trench environments; whether the members and functions of hadal microbial communities are common in trenches under geologically and oceanographically different settings or specific in each hadal environment; and if different, what types of factors constrain the compositions and functions of hadal microbial communities and how they are controlled

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