Abstract
We investigated the top 30-cm sediment prokaryotic community structure in 5-cm spatial resolution, at an active site of the Amsterdam mud volcano, East Mediterranean Sea, based on the 16S rRNA gene diversity. A total of 339 and 526 sequences were retrieved, corresponding to 25 and 213 unique (≥98% similarity) phylotypes of Archaea and Bacteria, respectively, in all depths. The Shannon-Wiener diversity index H was higher for Bacteria (1.92-4.03) than for Archaea (0.99-1.91) and varied differently between the two groups. Archaea were dominated by anaerobic methanotrophs ANME-1, -2 and -3 groups and were related to phylotypes involved in anaerobic oxidation of methane from similar habitats. The much more complex Bacteria community consisted of 20 phylogenetic groups at the phylum/candidate division level. Proteobacteria, in particular δ-Proteobacteria, was the dominant group. In most sediment layers, the dominant phylotypes of both the Archaea and Bacteria communities were found in neighbouring layers, suggesting some overlap in species richness. The similarity of certain prokaryotic communities was also depicted by using four different similarity indices. The direct comparison of the retrieved phylotypes with those from the Kazan mud volcano of the same field revealed that 40.0% of the Archaea and 16.9% of the Bacteria phylotypes are common between the two systems. The majority of these phylotypes are closely related to phylotypes originating from other mud volcanoes, implying a degree of endemicity in these systems.
Highlights
Mud volcanoes (MV) are areas of active fluid seepage occurring both on land and at the seafloor [50]
A total of 339 Archaea 16S rRNA gene sequences were retrieved which were attributed to 55 phylotypes distributed in all sediment layers and 25 of them were unique for the whole core
One ANME-1 phylotype was present at 0 (AMSMV-0-A18, 8.3%) and the same phylotype was retrieved at 5 cm.b.s.f
Summary
Mud volcanoes (MV) are areas of active fluid seepage occurring both on land and at the seafloor [50]. Active marine MV could be considered as analogue habitats of fluidized or mobile muds (sensu Aller et al [1]) since they consist of a mixture of fine-grained, creamy-textured sediment and fluids, expanding down to 1 m or deeper, these sediments can be remobilized due to irregular and unpredictable eruptions. Such habitats serve as efficient methane and sulfur reactors, hosting characteristically high bacterial and low archaeal diversity. It is expected that MV undergo temporal and spatial changes due to changes in gas/fluid fluxes, eruptions and gas hydrate association–dissociation, probably ensuing successive stages in microbial community structure and functioning
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