Abstract
The seafloor is a unique environment, which allows insights into how geochemical processes affect the diversity of biological life. Among its diverse ecosystems are deep-sea brine pools - water bodies characterized by a unique combination of extreme conditions. The ‘polyextremophiles’ that constitute the microbial assemblage of these deep hot brines have not been comprehensively studied. We report a comparative taxonomic analysis of the prokaryotic communities of the sediments directly below the Red Sea brine pools, namely, Atlantis II, Discovery, Chain Deep, and an adjacent brine-influenced site. Analyses of sediment samples and high-throughput pyrosequencing of PCR-amplified environmental 16S ribosomal RNA genes (16S rDNA) revealed that one sulfur (S)-rich Atlantis II and one nitrogen (N)-rich Discovery Deep section contained distinct microbial populations that differed from those found in the other sediment samples examined. Proteobacteria, Actinobacteria, Cyanobacteria, Deferribacteres, and Euryarchaeota were the most abundant bacterial and archaeal phyla in both the S- and N-rich sections. Relative abundance-based hierarchical clustering of the 16S rDNA pyrotags assigned to major taxonomic groups allowed us to categorize the archaeal and bacterial communities into three major and distinct groups; group I was unique to the S-rich Atlantis II section (ATII-1), group II was characteristic for the N-rich Discovery sample (DD-1), and group III reflected the composition of the remaining sediments. Many of the groups detected in the S-rich Atlantis II section are likely to play a dominant role in the cycling of methane and sulfur due to their phylogenetic affiliations with bacteria and archaea involved in anaerobic methane oxidation and sulfate reduction.
Highlights
The Red Sea represents a 450,000-km2 inlet of the Indian Ocean located between the African continent and the Arabian Peninsula
Chemical profiling of the sediments from brine pools Sediment were collected from Atlantis II (ATII), Discovery (DD), Chain Deep (CD) and an adjacent brine-influenced (BI) site (Fig. 1 and Table 1) as described in materials and methods
Carbon Hydrogen Nitrogen & Sulfur (CHN&S) profiling showed that the analyzed brine sediments and the adjacent BI sediments differed greatly in C and S content, whereas little variation was found in H (1.4–1.9% w/w) or N (,0.10 to 0.12% w/w) content (Table 2)
Summary
The Red Sea represents a 450,000-km inlet of the Indian Ocean located between the African continent and the Arabian Peninsula. Among the most intriguing ecological niches in the Red Sea are its deep-sea brines, which exhibit unique and diverse geochemical conditions [1]. The hot brine system at Atlantis II Deep (ATII) is the largest and best characterized pool in the Red Sea. Located at a depth of approximately 2200 m near the Central Rift (at around 21u209 N), it is less than 100 m thick, and covers an area of 60 km. The conditions in the Discovery Deep brine are less harsh and not as well described as Atlantis II, with relatively high concentrations of metals and a milder temperature of 44.8uC [12]
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