Relative Abundance and Diversity of Bacterial Methanotrophs at the Oxic-Anoxic Interface of the Congo Deep-Sea Fan.

Sandrine Bessette,Yann Moalic,Françoise Lesongeur,Laurent Toffin,Anne Godfroy,Sébastien Gautey

doi:10.3389/fmicb.2017.00715

Abstract

Sitting at ∼5,000 m water depth on the Congo-Angola margin and ∼760 km offshore of the West African coast, the recent lobe complex of the Congo deep-sea fan receives large amounts of fluvial sediments (3–5% organic carbon). This organic-rich sedimentation area harbors habitats with chemosynthetic communities similar to those of cold seeps. In this study, we investigated relative abundance, diversity and distribution of aerobic methane-oxidizing bacteria (MOB) communities at the oxic–anoxic interface of sedimentary habitats by using fluorescence in situ hybridization and comparative sequence analysis of particulate mono-oxygenase (pmoA) genes. Our findings revealed that sedimentary habitats of the recent lobe complex hosted type I and type II MOB cells and comparisons of pmoA community compositions showed variations among the different organic-rich habitats. Furthermore, the pmoA lineages were taxonomically more diverse compared to methane seep environments and were related to those found at cold seeps. Surprisingly, MOB phylogenetic lineages typical of terrestrial environments were observed at such water depth. In contrast, MOB cells or pmoA sequences were not detected at the previous lobe complex that is disconnected from the Congo River inputs.

Highlights

Deep-sea fans, known as deep-sea turbidite systems, trap enormous amounts of terrestrial organic matter (OM) inputs delivered from continental shelves to deep ocean basins by rivers
Relative bacterial abundances detected by fluorescence in situ hybridization (FISH) were higher in chemosynthetic habitats of the recent lobe complex than in adjacent sediment (Col_C_BS) of the same lobe complex (0.1 ± 0.0 × 107 cell/ml) or than in sediment from the previous lobe complex (Col_E_BS; 0.1 ± 0.0 × 107 cell/ml) (Table 2)
The highest relative number of methane-oxidizing bacteria (MOB) was observed in black patch sediment (Col_C_BP; 2.8 ± 0.2 × 106 cell/ml) while the lowest MOB abundance was observed in adjacent sample (Col_C_BS; 0.49 ± 0.1 × 106 cell/ml)

Summary

Introduction

Deep-sea fans, known as deep-sea turbidite systems, trap enormous amounts of terrestrial organic matter (OM) inputs delivered from continental shelves to deep ocean basins by rivers. Due to its direct connection to the Congo River, the second largest river in the world in terms of fluvial discharge, Methanotrophs in Organic-Rich Sediments continuous massive sedimentary inputs are transferred via turbidity currents following the path of the canyon deeply incised in the shelf (Khripounoff et al, 2003), regardless of sea level fluctuations (Droz et al, 2003). These sedimentary inputs flow 760 km off the Congo-Angola margin along the presentday active channel-levee system, which ends with lobe-shaped sedimentary deposits called the recent lobe complex (Savoye et al, 2009). These CH4-enriched sedimentary areas support remarkable chemosynthetic fauna on the seafloor that resemble the chemosynthetic communities associated with cold seeps (Rabouille et al, 2016)

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