Thiosulfate Stimulation Of Bacterial Communities In The Deep Ocean

Chemoautotrophic prokaryotes inhabit the ocean down to the bathypelagic realm and play a key function in the global carbon cycle. However, their potential metabolic flexibility in response to pulses of energy sources and the subsequent stimulation of the bulk prokaryotic community in the deep ocean have been rarely characterized. In this study, we used incubations with the thymidine analog bromodeoxyuridine (BrdU) in combination with next generation sequencing to characterize the active prokaryotic community. Samples collected from mesopelagic (500 m) and bathypelagic (down to 2750 m) realm of the North Atlantic Drift province (43-45ºN) were incubated with thiosulfate or thiosulfate plus a mix of organic compounds. A fast depth-specific change of the active community was observed following the addition of the substrates, while no significant change in the bulk community occurred, with some exceptions. Typically chemoautotrophic organisms, such as SAR324, Nitrospina and SUP05, were only stimulated in discrete bathypelagic samples. Oligotyping analysis of the main phylogenetic groups identified a small group of very closely related microbes triggered by the addition of the different substrates. Taken together, our results indicate the existence of several ecotypes of closely related microbes each of them occupying a specific ecological niche in the seemingly homogenous deep ocean.