Microbial life in the Lake Medee, the largest deep-sea salt-saturated formation

Abstract

Deep-sea hypersaline anoxic lakes (DHALs) of the Eastern Mediterranean represent some of the most hostile environments on our planet. We investigated microbial life in the recently discovered Lake Medee, the largest DHAL found to-date. Medee has two unique features: a complex geobiochemical stratification and an absence of chemolithoautotrophic Epsilonproteobacteria, which usually play the primary role in dark bicarbonate assimilation in DHALs interfaces. Presumably because of these features, Medee is less productive and exhibits reduced diversity of autochthonous prokaryotes in its interior. Indeed, the brine community almost exclusively consists of the members of euryarchaeal MSBL1 and bacterial KB1 candidate divisions. Our experiments utilizing cultivation and [14C]-assimilation, showed that these organisms at least partially rely on reductive cleavage of osmoprotectant glycine betaine and are engaged in trophic cooperation. These findings provide novel insights into how prokaryotic communities can adapt to salt-saturated conditions and sustain active metabolism at the thermodynamic edge of life.

Inter-comparison of the potentially active prokaryotic communities in the halocline sediments of Mediterranean deep-sea hypersaline basins

“…Despite findings suggesting that chemolithoautotrophy is the dominant metabolic trait in halocline waters of Mediterranean DHABs (Yakimov et al 2013), the OTUs detected in our study represent prokaryotes that need organic substrates for growth. Available organic carbon that reaches the seafloor of Mediterranean DHABs is expected to be relatively recalcitrant, compared to newer, more labile carbon sources in the overlying water column, but there is no information on available electron donors in DHAB sediments.…”

“…While new cell morphologies and ecophysiological traits have been assigned to some of these microorganisms, only recently a more specific picture of the metabolic activities of DHAB microorganisms has started to emerge, e.g. S--oxidizing chemolithotrophy, microaerophilic autotrophy, heterotrophic sulfate reduction, methanogenesis and anaerobic methane oxidation (Borin et al 2009;La Cono et al 2011;Ferrer et al 2012;Pachiadaki et al 2014;Yakimov et al 2013;Alcaide et al 2015). In spite of these recent advances, we still know little about how these microorganisms survive and grow under the prevailing conditions of the DHABs.…”

Contrasting taxonomic stratification of microbial communities in two hypersaline meromictic lakes

“…The most abundant OTUs belonging to Methanobacteriales or MSBL1 were highly similar (95-99%) to unclassified sequences recovered from other hypersaline meromictic lakes, solar salterns sediments or deep sea-hypersaline anoxic basins, indicating the existence of a yet-undescribed methanogenic group present in extreme hypersaline habitats. Although this assumption is supported by a recent study on Medee brines (Yakimov et al, 2013), in which MSBL1 candidate division was shown to be responsible for the methanogenic fermentation of trimethylamine, further experiments using cultivation and 14 C-assimilation are needed to unambiguously describe the methanogenesis in these high-salt ecosystems.…”

Comparative genomics reveals adaptations of a halotolerant thaumarchaeon in the interfaces of brine pools in the Red Sea

“…As such, the low-energy yield of nitrification may preclude this process at high salt concentrations, which may partially explain the reduced biomass of AOA and the higher density and phylogenetic diversity of sulfur oxidizers in the BSI layer (Yakimov et al, 2007(Yakimov et al, , 2013. Although the upper salinity limit for autotrophic ammonia oxidation is still uncertain, nitrification appears to be constrained at salt concentrations exceeding 100 g l -1 (Oren, 2011).…”