oa Geochemical Control on Microbial Lipid Distributions in Hydrothermal Sediments Off Milos (GREECE)

We studied how microorganisms adapt their lipid inventory to extreme environmental conditions at hydrothermal vents of Milos, Greece. We examined the lipid compositions in three sediment cores from sites between 100 and 200 m water depth, representing: (i) a redox gradient in Eh and pH values, (ii) fully reduced conditions with T of up to 100°C, and (iii) a site devoid of hydrothermal influence. Using a non-metric multidimensional scaling (NMDS) analysis, we investigated the site-specific lipid distribution patterns in relation to porewater chemistry and environmental conditions. While bacterial-derived FAs and DAGEs appeared to be little affected by hydrothermalism, tetraether classes strongly varied in abundance with geochemical gradients. Of the huge variety of tetraethers, multiple methylated archaeal iGMGTs and bacterial brGDGT/GMGTs are the main compounds produced at higher T. The former, however, even stronger correlated with high DIC as well as low pH and Eh values. Our results challenge the assumption that temperature alone dictates microbial lipid adaptations and suggest that the activity of microbial life in hydrothermal environments is similarly controlled by varying redox gradients as well as the availability of DIC as carbon and likely sulfur species as energy source.