Drivers of Bacterial α- and β-Diversity Patterns and Functioning in Subsurface Hadal Sediments.

Eugenio Rastelli,Antonio Dell’Anno,Manabu Nishizawa,Takuro Nunoura,Marco Lo Martire,Hidetaka Nomaki,Cinzia Corinaldesi,Michael Tangherlini,Roberto Danovaro

doi:10.3389/fmicb.2019.02609

Abstract

Oceanic trenches at hadal (>6,000 m) depths are hot spots of organic matter deposition and mineralization and can host abundant and active bacterial assemblages. However, the factors able to shape their biodiversity and functioning remain largely unexplored, especially in subsurface sediments. Here, we investigated the patterns and drivers of benthic bacterial α- and β-diversity (i.e., OTU richness and turnover diversity) along the vertical profile down to 1.5 m sediment depth in the Izu-Bonin Trench (at ~10,000 m water depth). The protease and glucosidase enzymatic activity rates were also determined, as a proxy of organic matter degradation potential in the different sediment layers. Molecular fingerprinting based on automated ribosomal intergenic spacer analysis (ARISA) indicated that the α-diversity of bacterial assemblages remained high throughout the vertical profile and that the turnover (β-) diversity among sediment horizons reached values up to 90% of dissimilarity. Multivariate distance-based linear modeling (DISTLM) pointed out that the diversity and functioning of the hadal bacterial assemblages were influenced by the variability of environmental conditions (including the availability of organic resources and electron donors/acceptors) and of viral production rates along the sediment vertical profile. Based on our results, we can argue that the heterogeneity of physical-chemical features of the hadal sediments of the Izu-Bonin Trench contribute to increase the niches availability for different bacterial taxa, while viruses contribute to maintain high levels of bacterial turnover diversity and to enhance organic matter cycling in these extremely remote and isolated ecosystems.

Highlights

The hadal biosphere is almost exclusively represented by ultra-abyssal trenches and comprises some of the most remote and inaccessible deep-sea environments, whose microbial ecology is still largely unexplored (Jamieson, 2015, 2018; Jamieson et al, 2018)
We found a positive and significant correlation between the rates of carbon release from viral lysis of bacteria and the organic matter turnover rates determined by enzymatic digestion of carbohydrates and proteins in the hadal sediments (y = 1.31; x = +4.46 × 10−2; R2 = 0.784; Figure 8)
We show here high levels of α- and β-diversity of the bacterial assemblages along the vertical profile down to 1.55 mbsf in one of the deepest points of the largest hadal habitat on Earth: the Izu-Bonin Trench (Northwest Pacific Ocean)

Summary

Introduction

The hadal biosphere is almost exclusively represented by ultra-abyssal trenches and comprises some of the most remote and inaccessible deep-sea environments, whose microbial ecology is still largely unexplored (Jamieson, 2015, 2018; Jamieson et al, 2018). Independent evidence suggests that the enhanced deposition of sinking and resuspended particles to the bottom due to the peculiar “V”-shaped trench topography (Wenzhöfer et al, 2016; Xu et al, 2018) can support more abundant and metabolically active bacterial assemblages than in the abyssal surroundings (Danovaro et al, 2003; Glud et al, 2013; Leduc et al, 2016; Wenzhöfer et al, 2016) This suggests that hadal bacteria interact with and are influenced by changes in the trench sedimentation regime. This feature has been suggested to contribute to influence the composition of bacterial assemblages down the hadal sediment profile (Nunoura et al, 2013, 2018; Li et al, 2019: Peoples et al, 2019)

Methods

Results

Conclusion