Sulfur cycling and methanogenesis primarily drive microbial colonization of the highly sulfidic Urania deep hypersaline basin.
Urania basin in the deep Mediterranean Sea houses a lake that is >100 m deep, devoid of oxygen, 6 times more saline than seawater, and has very high levels of methane and particularly sulfide (up to 16 mM), making it among the most sulfidic water bodies on Earth. Along the depth profile there are 2 chemoclines, a steep one with the overlying oxic seawater, and another between anoxic brines of different density, where gradients of salinity, electron donors and acceptors occur. To identify and differentiate the microbes and processes contributing to the turnover of organic matter and sulfide along the water column, these chemoclines were sampled at a high resolution. Bacterial cell numbers increased up to a hundredfold in the chemoclines as a consequence of elevated nutrient availability, with higher numbers in the upper interface where redox gradient was steeper. Bacterial and archaeal communities, analyzed by DNA fingerprinting, 16S rRNA gene libraries, activity measurements, and cultivation, were highly stratified and metabolically more active along the chemoclines compared with seawater or the uniformly hypersaline brines. Detailed analysis of 16S rRNA gene sequences revealed that in both chemoclines delta- and epsilon-Proteobacteria, predominantly sulfate reducers and sulfur oxidizers, respectively, were the dominant bacteria. In the deepest layers of the basin MSBL1, putatively responsible for methanogenesis, dominated among archaea. The data suggest that the complex microbial community is adapted to the basin's extreme chemistry, and the elevated biomass is driven largely by sulfur cycling and methanogenesis.
Borin
Sara
S
Department of Food Science, and Microbiology, Consorzio Nazionale Interuniversitario per le Scienze del Mare, Ulr Università degli Studi di Milano, 20133 Milan, Italy.
Brusetti
Lorenzo
L
Mapelli
Francesca
F
D'Auria
Giuseppe
G
Brusa
Tullio
T
Marzorati
Massimo
M
Rizzi
Aurora
A
Yakimov
Michail
M
Marty
Danielle
D
De Lange
Gert J
GJ
Van der Wielen
Paul
P
Bolhuis
Henk
H
McGenity
Terry J
TJ
Polymenakou
Paraskevi N
PN
Malinverno
Elisa
E
Giuliano
Laura
L
Corselli
Cesare
C
Daffonchio
Daniele
D
D001105:Archaea / Q000378:metabolism*; D001419:Bacteria / Q000378:metabolism*; D017753:Ecosystem; D008345:Manganese / Q000378:metabolism; D008969:Molecular Sequence Data; D009566:Nitrates / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D054712:Salinity; D012623:Seawater / Q000382:microbiology*; D013455:Sulfur / Q000378:metabolism*; D014867:Water / Q000378:metabolism
D009566:Nitrates; D014867:Water; D008345:Manganese; D013455:Sulfur; D010100:Oxygen