Colonization of plant substrates at hydrothermal vents and cold seeps in the northeast Atlantic and Mediterranean and occurrence of symbiont-related bacteria.

Kamil M Szafranski,Marina R Cunha,Philippe Deschamps,Sã©Bastien Duperron,Sylvie M Gaudron

doi:10.3389/fmicb.2015.00162

Abstract

Reducing conditions with elevated sulfide and methane concentrations in ecosystems such as hydrothermal vents, cold seeps or organic falls, are suitable for chemosynthetic primary production. Understanding processes driving bacterial diversity, colonization and dispersal is of prime importance for deep-sea microbial ecology. This study provides a detailed characterization of bacterial assemblages colonizing plant-derived substrates using a standardized approach over a geographic area spanning the North-East Atlantic and Mediterranean. Wood and alfalfa substrates in colonization devices were deployed for different periods at 8 deep-sea chemosynthesis-based sites in four distinct geographic areas. Pyrosequencing of a fragment of the 16S rRNA-encoding gene was used to describe bacterial communities. Colonization occurred within the first 14 days. The diversity was higher in samples deployed for more than 289 days. After 289 days, no relation was observed between community richness and deployment duration, suggesting that diversity may have reached saturation sometime in between. Communities in long-term deployments were different, and their composition was mainly influenced by the geographical location where devices were deployed. Numerous sequences related to horizontally-transmitted chemosynthetic symbionts of metazoans were identified. Their potential status as free-living forms of these symbionts was evaluated based on sequence similarity with demonstrated symbionts. Results suggest that some free-living forms of metazoan symbionts or their close relatives, such as Epsilonproteobacteria associated with the shrimp Rimicaris exoculata, are efficient colonizers of plant substrates at vents and seeps.

Highlights

Hydrothermal vents and other chemosynthesis-based ecosystems like cold seeps are deep-sea hotspots of primary production, which is ensured by chemoautotrophic prokaryotes, many of which live in symbiosis with various metazoans (Van Dover, 2000; Dubilier et al, 2008)
The deep-sea ecosystem can benefit from significant input of exogenous sources of carbon such as plant remains of different origins, like sunken wood (Wolff, 1979)
PREPARATION OF DATASETS Bacterial diversity was investigated on 25 individual CHEMECOLIs filled with either pine wood cubes or alfalfa and deployed for periods of 10–1112 days in four areas in the North East Atlantic and Mediterranean

Summary

Introduction

Hydrothermal vents and other chemosynthesis-based ecosystems like cold seeps are deep-sea hotspots of primary production, which is ensured by chemoautotrophic prokaryotes, many of which live in symbiosis with various metazoans (Van Dover, 2000; Dubilier et al, 2008). The aims are to identify bacteria colonizing the substrates, to evaluate the effect of region, type of substrate, depth, duration of deployment, and temperature on the bacterial assemblages, and to screen for potential free-living forms or relatives of metazoan-associated chemosynthetic symbionts. Screening for symbiont-related sequences was made on a reduced dataset including 332621 sequences representing 2641 OTUs. Community composition and comparisons were performed on a dataset containing only abundant sequences, overall 306716 sequences in 658 OTUs. On average, dataset sizes were reduced by 35, 41, and 46% of total read numbers and contained 7012, 6397, and 5898 sequences per sample (2 replicate samples per CHEMECOLI).

Results

Conclusion