Microbial Communities in the Chemocline of a Hypersaline Deep-Sea Basin (Urania Basin, Mediterranean Sea)

Abstract

The Urania basin is a hypersaline sulfidic brine lake at the bottom of the eastern Mediterranean Sea. Since this basin is located at a depth of ϳ3,500 m below the sea surface, it receives only a small amount of phytoplankton organic carbon. In the present study, the bacterial assemblages at the interface between the hypersaline brine and the overlaying seawater were investigated. The sulfide concentration increased from 0 to 10 mM within a vertical interval of 5 m across the interface. Within this chemocline, the total bacterial cell counts and the exoenzyme activities were elevated. Employing 11 cultivation methods, we isolated a total of 70 bacterial strains. The 16S ribosomal DNA sequences of 32 of the strains were identical to environmental sequences detected in the chemocline by culture-independent molecular methods. These strains were identified as flavobacteria, Alteromonas macleodii, and Halomonas aquamarina. All 70 strains could grow chemoorganoheterotrophically under oxic conditions. Sixty-six strains grew on peptone, casein hydrolysate, and yeast extract, whereas only 15 strains did not utilize polymeric carbohydrates. Twenty-one of the isolates could grow both chemoorganotrophically and chemolithotrophically. While the most probable numbers in most cases ranged between 0.006 and 4.3% of the total cell counts, an unsually high value of 54% was determined above the chemocline with media containing amino acids as the carbon and energy source. Our results indicate that culturable bacteria thriving at the oxic-anoxic interface of the Urania basin differ considerably from the chemolithoautotrophic bacteria typical of other chemocline habitats.

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

“…A common theme among all these DHABs is that the transition from the overlying seawater to the brine-commonly referred to as the brine-seawater interface (BSI), forms a particularly interesting environment, which is characterized by steep gradients of temperature, salinity, pH and dissolved oxygen (Eder et al, 2001;Sass et al, 2001;Daffonchio et al, 2006;Borin et al, 2009;Swift et al, 2012). Here also, the concentration of nutrients (organic carbon, NH 4 þ and NO 3 -) and minerals are a few orders of magnitude higher than in the overlying seawater (Ryan et al, 1969;Anschutz et al, 1999;Bougouffa et al, 2013).…”

Unveiling microbial activities along the halocline of Thetis, a deep-sea hypersaline anoxic basin

“…Studies of Discovery, L'Atalante, Urania, Thetis and Bannock basins revealed that DHAB interfaces harbor abundant and diverse microbial communities that include numerous novel candidate divisions that are more productive than most pelagic marine systems (see, for example, Sass et al, 2001;Van Der Wielen et al, 2005;Yakimov et al, 2007;Edgcomb et al, 2009;Stock et al, 2012). Functional analyses of these communities based on PCR amplification of key functional genes as well as activity measurements revealed sulfur cycling and methanogenesis to be dominant prokaryotic metabolic processes supporting life in DHABs and contributing to observed elevated biomass in DHAB haloclines (Daffonchio et al, 2006;Yakimov et al, 2007;Borin et al, 2009).…”

Protistan community patterns within the brine and halocline of deep hypersaline anoxic basins in the eastern Mediterranean Sea

“…Deep hypersaline anoxic basins (DHABs) in the Mediterranean and Red Sea have provided exciting new insights into novel microbial diversity and have already extended our knowledge of the environmental factors that define the limits of life (Eder et al 2001;Eder et al 1999;Eder et al 2002;Sass et al 2001;van der Wielen et al 2005;van der Wielen and Heijs 2007;Yakimov et al 2007b). …”