Mediterranean deep-sea brine lakes: unique terrestrial environments and analogues to putative subsurface ocean on Europa
Final Report Abstract
The world’s deepest and most hypersaline anoxic lakes (L’Atalante, Bannock, Discovery and Urania), occurring on the seafloor of the eastern Mediterranean Sea, represent one of the most hostile environments on Earth and may serve as analogues for similar potentially life-containing environments of Mars and deep saline cold waters on Europa. Some major discoveries have been made in recent years on very peculiar forms of microbial life adapted to such environments. A first attempt to functionally analyse the metagenome from Urania Basin seawater-brine interface has yielded a number of microbial enzymes which exhibit unusual structures, as well as biochemical parameters and substrate specificities. The aim of the present study was to characterize for the first time metabolically active prokaryotic assemblage thriving in a mud vent habitat underneath the deep-sea brine lakes using rRNA-based phylogenetic analysis of a clone library. The metabolically active prokaryotic community showed a great genetic diversity. Most members of the community appeared to be affiliated to yet uncultured organisms from similar ecosystems, i.e., deep-sea hypersaline basins and hydrothermal vents. The bacterial clone library was dominated by phylotypes affiliated with the epsilon-Proteobacteria subdivision recognized as an ecologically significant group of bacteria inhabiting deep-sea hydrothermal environments. Almost 18% of all bacterial clones were related to delta-Proteobacteria, suggesting that sulfate reduction is one of the dominant metabolic processes occurring in mud fluids. The remaining bacterial phylotypes were related to alpha- and beta-Proteobacteria, Actinobacteria, Bacteroides, Deinococcus-Thermus, KB1 and OP-11 candidate divisions. Moreover, a novel monophyletic clade, deeply branched with unaffiliated 16S rDNA clones was also retrieved from deepsea sediments and halocline of Urania Basin. Archaeal diversity was much lower and detected phylotypes included organisms affiliated exclusively with the Euryarchaeota. More than 96% of the archaeal clones belonged to the MSBL-1 candidate order recently found in hypersaline anoxic environments, such as endoevaporitic microbial mats, Mediterranean deep-sea mud volcanoes and anoxic basins. Another direction of our study is dedicated to Ferroplasma which belongs to the order Thermoplasmatales (Euryarchaeota, Archaea), and which contains the most acidophilic microbes yet known. Ferroplasma species live in environments containing sulphidic ores such as pyrite and characterized by low pH and high concentrations of ferrous iron and other heavy metals. F. acidiphilum strain YT is a chemoautotroph that grows optimally at pH 1.7 and gains energy by oxidizing ferrous iron and carbon by the fixation of carbon dioxide. Its metabolic properties make this microorganism a good candidate to survive under martial conditions. We showed recently that an α-glucosidase and few other enzymes of F. acidiphilum were ironcontaining metalloenzymes, a property not known for any other enzymes of corresponding classes. The question arose whether other proteins of this peculiar organism were iron-metalloproteins. We have performed a “luminal proteome”, study of this organism which is based on high-resolution inductively coupled plasma mass spectroscopy (ICP-MS) coupled with de-novo protein sequencing. Which revealed the presence of iron at concentrations ranging from 0.1 to 2.1 ng in all 87 protein spot samples resolved. Furthermore after analysis of the metal content in conventionally-stained gels we have shown that 86% of 189 investigated cellular proteins of F. acidiphilum were iron-metalloproteins. Although about 15% of them were typical metalloproteins, the others were proteins that have until now never or rarely been shown to contain iron. Those included proteins with deduced structural, chaperone and catalytic roles, not described as iron-metalloproteins in any other organism so far investigated. F. acidiphilum therefore has a currently unique iron-protein-dominated cellular machinery and biochemical phylogeny. The data obtained through this study represents a new insight into microbial life in extreme ecosystems and may form the basis for future research in this field and in astrobiology.
Publications
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(2006) Stratified prokaryote network in the oxic-anoxic transition of a deep-sea halocline. Nature. 440(7081):203-7
Daffonchio D, Borin S, Brusa T, Brusetti L, van der Wielen PW, Bolhuis H, Yakimov MM, D'Auria G, Giuliano L, Marty D, Tamburini C, McGenity TJ, Hallsworth JE, Sass AM, Timmis KN, Tselepides A, de Lange GJ, Hubner A, Thomson J, Varnavas SP, Gasparoni F, Gerber HW, Malinverno E, Corselli C, Garcin J, McKew B, Golyshin PN, Lampadariou N, Polymenakou P, Calore D, Cenedese S, Zanon F, Hoog S
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(2006) The 'pH optimum anomaly' of intracellular enzymes of Ferroplasma acidiphilum. Environ Microbiol. 8(3):416-25
Golyshina OV, Golyshin PN, Timmis KN, Ferrer M
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(2007) Limits of life in MgCl2-containing environments: chaotropicity defines the window. Environ Microbiol. 9(3):801-13
Hallsworth JE, Yakimov MM, Golyshin PN, Gillion JL, D'Auria G, de Lima Alves F, La Cono V, Genovese M, McKew BA, Hayes SL, Harris G, Giuliano L, Timmis KN, McGenity TJ
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(2007) Microbial Community of a Hydrothermal Mud Vent Underneath the Deep-Sea Anoxic Brine Lake Urania (Eastern Mediterranean). Orig Life Evol Biosph. 37(2):177-88
Yakimov M.M., Giuliano L., Cappello S., Denaro R., Golyshin P.
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(2007) The cellular machinery of Ferroplasma acidiphilum is iron-protein-dominated. Nature. 445(7123):91-4
Ferrer M., Golyshina O.V., Beloqui A., Golyshin P.N, Timmis K.N.
