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Microbial diversity and biogeochemistry of Milos (Aegean Sea, Greece) hydrothermal vents


Santi,  Ioulia
IMPRS MarMic, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Santi, I. (2013). Microbial diversity and biogeochemistry of Milos (Aegean Sea, Greece) hydrothermal vents. Master Thesis, University of Bremen, Bremen / Germany.

Cite as: http://hdl.handle.net/21.11116/0000-0001-C72B-F
Hydrothermal vents, characterized by extreme environmental conditions, like high temperatures and steep geochemical gradients, are considered to be among the most intriguing areas in marine research. In this study, we investigated a shallow-water hydrothermal system found off the island of Milos, in the Aegean Volcanic Arc (Eastern Mediterranean Sea). In particular, we explored the geochemistry, based on porewater analysis and on in situ microsensor measurements, and the microbial communities, based on molecular fingerprinting techniques, in the hydrothermal sediment along a temperature gradient towards the center of the vent. We have observed that on a spatial scale of less than 10 m, from the unaffected to the venting sites, the sediment geochemistry changed substantially. The in situ microgradients of O2, H2S, pH and temperature revealed different microenvironments in the hydrothermally impacted sediment, comprising a variety of potential microniches for diverse microbial communities. However, differences in the bacterial community structure were not that prominent between the different venting sites. We found considerably different community structure and composition between the venting and the unaffected sites, as well as, decrease in operational taxonomic units (OTUs) richness with increasing hydrothermal activity. We believe that these differences between community structure and OTU richness are due to the extreme hydrothermal conditions; thus bacterial communities are selected based on their metabolic capabilities and their ability to tolerate extreme conditions. Indeed, when we tried to reveal the main factors that control the microbial communities, sediment geochemistry and especially H2S and pH, were the major parameters influencing the variation in the bacterial community structure. To test how varying H2S concentrations and fluid flow velocities affect the biogeochemistry of vent-impacted sediment, ex situ simulations were performed. Based on lower than expected H2S concentrations measured in the treated sediment, we assume that in addition to the typical consumption of sulfide in the oxic-anoxic interface, processes occurring deeper in the sediment (bellow 3 cm) are responsible for additional removal of sulfide from the system. Overall, several different geochemical microenvironments were revealed along with a spatial pattern in the microbial communities of the different hydrothermally impact sediment.