Particle-Attached and Free-Living Archaeal Communities in the Benthic Boundary Layer of the Mariana Trench.

Hongmei Jing,Yu Zhang,Liping Zheng,Hongbin Liu,Wenda Zhu

doi:10.3389/fmicb.2018.02821

Abstract

The benthic boundary layer (BBL) is the part of the water column that is situated near to the sediment surface, where active oceanic biogeochemical cycling occurs. Archaea play an important role in mediating this cycling, however, their composition and diversity in the BBL remain largely unknown. We investigated the community composition and abundance of both particle-attached (PA) and free-living (FL) archaea in the BBL on the slopes of the Mariana Trench using Illumina sequencing and quantitative PCR (qPCR), at both the DNA and RNA levels. Our results showed that Thaumarchaeota (>90%) and Woesearchaeota (1–10%) dominated in all the BBL samples, and that the former was composed mainly of Marine Group I (MGI). A clear separation of PA and FL samples was observed, and they showed a high level of similarity to the subsurface sediments and the water column, respectively. No significant differences were detected in the archaeal communities located in the southern and northern slopes of the Mariana Trench, or between the levels of DNA and RNA. However, lower RNA/DNA ratios (estimated by qPCR) were found in the PA samples than in the FL samples, indicating higher transcriptional activities in the FL fractions. A distinct archaeal community structure was found in the middle of the trench when compared with samples collected at the same depth at other stations along the trench slopes. This indicates that a dynamic deep current might affect the distribution of organic matter on the slopes. Our study provides direct information regarding the archaeal communities in the BBL of the Mariana Trench. We suggest that this might promote further exploration of the ecological roles and microbial processes of such communities located in deep-sea ecosystems.

Highlights

The benthic boundary layer (BBL) is defined as the bottom layer of the water column, which lies directly adjacent to the seabed; it is composed of different sub-layers, which range in depth from several meters to just a few millimeters (Turley, 2000; Chong et al, 2017)
Recent studies suggested that the abundance of archaea in the deep-sea BBL is significantly affected by the incorporation rates of carbon fixation in this zone (Dang et al, 2013; Molari et al, 2013)
We investigated the abundance and diversity of PA and FL archaea at both the DNA and RNA levels in the BBL along the slopes of the Mariana Trench

Summary

Introduction

The benthic boundary layer (BBL) is defined as the bottom layer of the water column, which lies directly adjacent to the seabed; it is composed of different sub-layers, which range in depth from several meters to just a few millimeters (Turley, 2000; Chong et al, 2017). Archaea in Mariana Trench the sediment into the water column (Percuoco et al, 2015; Topping et al, 2016). Research into the deep-sea BBL has attracted much attention (Turley, 2000; Dell’Anno and Danovaro, 2005; Danovaro et al, 2014; Tarn et al, 2016), studies have up until recently been limited by instrumentation constraints. Recent studies suggested that the abundance of archaea in the deep-sea BBL is significantly affected by the incorporation rates of carbon fixation in this zone (Dang et al, 2013; Molari et al, 2013). Environmental factors that might affect the diversity and distribution of Thaumarchaeota in the deep-sea BBL remain unclear

Methods

Results

Discussion

Conclusion