Life on the edge: Active microbial communities in the Kryos MgCl2-brine basin at very low water activity

• Published in: The ISME Journal
• Main Authors: Steinle, Lea, Knittel, Katrin, Felber, Nicole, Casalino, Claudia, de Lange, Gert, Tessarolo, Chiara, Stadnitskaia, Alina, Sinninghe Damsté, Jaap S., Zopfi, Jakob, Lehmann, Moritz F., Treude, Tina
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer Nature 2018
• Subjects: VDP::Mathematics and natural science: 400::Zoology and botany: 480::Marine biology: 497; VDP::Matematikk og Naturvitenskap: 400::Zoologiske og botaniske fag: 480::Marinbiologi: 497; VDP::Mathematics and natural science: 400::Basic biosciences: 470::General microbiology: 472; VDP::Matematikk og Naturvitenskap: 400::Basale biofag: 470::Generell mikrobiologi: 472; VDP::Mathematics and natural science: 400::Basic biosciences: 470::Biochemistry: 476; VDP::Matematikk og Naturvitenskap: 400::Basale biofag: 470::Biokjemi: 476; Arctic
• Online Access: https://hdl.handle.net/10037/15059; https://doi.org/10.1038/s41396-018-0107-z

Source at https://doi.org/10.1038/s41396-018-0107-z . The Kryos Basin is a deep-sea hypersaline anoxic basin (DHAB) located in the Eastern Mediterranean Sea (34.98°N 22.04°E). It is filled with brine of re-dissolved Messinian evaporites and is nearly saturated with MgCl 2 -equivalents, which makes this habitat extremely challenging for life. The strong density difference between the anoxic brine and the overlying oxic Mediterranean seawater impedes mixing, giving rise to a narrow chemocline. Here, we investigate the microbial community structure and activities across the seawater–brine interface using a combined biogeochemical, next-generation sequencing, and lipid biomarker approach. Within the interface, we detected fatty acids that were distinctly 13 C-enriched when compared to other fatty acids. These likely originated from sulfide-oxidizing bacteria that fix carbon via the reverse tricarboxylic acid cycle. In the lower part of the interface, we also measured elevated rates of methane oxidation, probably mediated by aerobic methanotrophs under micro-oxic conditions. Sulfate reduction rates increased across the interface and were highest within the brine, providing first evidence that sulfate reducers (likely Desulfovermiculus and Desulfobacula ) thrive in the Kryos Basin at a water activity of only ~0.4 A w . Our results demonstrate that a highly specialized microbial community in the Kryos Basin has adapted to the poly-extreme conditions of a DHAB with nearly saturated MgCl 2 brine, extending the known environmental range where microbial life can persist.