Molecular ecology of deep-sea hydrothermal plumes

Abstract

Hydrothermal plumes are considered ephemeral habitats in the deep-sea and are reported to serve as hotspots for microbial biomass. The chemolithoautotrophic microbial communities form the basis of the food web in the resource-limited deep-sea and contribute to biogeochemical cycles over larger spatial scales. Despite their influence on biogeochemistry, a comprehensive analysis of microbial clades inhabiting hydrothermal plumes, their metabolism and distribution in the open-ocean is lacking. In this thesis, I investigated the communities of ten hydrothermal plumes, located in the Atlantic and Pacific oceans, originating at different depths and characterized by distinct chemical conditions. In these plumes, the dynamics and ecological function of the dominant microbial clades were investigated and ecological niches subsequently described. The first study identified and described the niches of three new SUP05 species in three sulfur rich plumes. The niche partitioning between SUP05 species was shown to be driven by depth and minor variations in environmental parameters. Based on differences in species distribution between vent sites and open-ocean, we propose that plumes serve as growth chambers for SUP05 species, from which they are released into the surrounding water. The investigation of four plumes originating from hydrothermally active volcanoes in the South Pacific Ocean elucidated a dominance of the alkane-degrading Alcanivorax. Results of our analysis, revealed a niche partitioning driven by depth and the complexity of hydrocarbons. We hypothesized that the Alcanivorax genus could be used as an indicator of environmental perturbations, such as hydrocarbon leakage from the seabed. Finally, the third study characterized the microbial community of four hydrothermal plumes in the Mid-Atlantic Ridge (MAR). The prominent taxa in these hydrogen-rich plumes were the SUP05 clade and Sulfurimonas. The high abundance of Sulfurimonas and SUP05 pointed towards a niche partitioning between the two clades, potentially driven by oxygen and hydrogen concentrations. The results of this thesis provide valuable information on the ecology of microbial communities inhabiting diverse hydrothermal plumes, their metabolisms and their ecological niches. With this, I show how we can move towards predictive ecology of plume communities. Furthermore, the data collected and analyzed from plumes in this study, considerably expands the currently available plume data and can serve as a valuable resource in future studies.