Microcosm Culture of a Shallow Hydrothermal Water Reveals a Shift of Microbial Communities

Hydrothermal vents are extreme environments based on complex ecological dynamics, due to harsh conditions. They are considered excellent model systems for studying community responses to climate change and ocean acidification scenarios. The study was aimed at setting up a microcosm experiment by using water samples collected shallow hydrothermal vents in Levante Bay (Vulcano Island, Aeolian Islands, Italy), to check differences in the taxonomic composition of microbial communities over a time of 90 days. The microbial community was elucidated by using enzymatic activity measurements and physiological profiles, total cell abundance estimations, total/respiring cell ratio, next generation sequencing techniques and CARD-FISH analysis to define the abundance of the metabolically active fraction within the microbial communities. The results showed a fairly stable community into the microcosm, represented almost entirely by Firmicutes (95<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">%</sup>) and Proteobacteria (2.6<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">%</sup>) members. A significant dominance of the Novibacillus genus was highlighted. The in situ hybridization results demonstrated that the community was active, with a percentage of 52 % of metabolically active cells.