Microbial diversity in deep hypersaline anoxic basins

Deep hypersaline anoxic basins (DHABs) have been discovered on the seafloor in different oceanic regions, such as the Gulf of Mexico (Shokes et al. 1977), the Red Sea (Pautot et al. 1984) and the Eastern Mediterranean Sea (Jongsma et al. 1983; Dupré et al. 2007). DHABs contain brines that due to their temperature and/or salinity do not mix with the upper seawater layers and lead to the stratification of the water column. Gradients of oxygen, sulphide, ammonium and other electron acceptors/donors can occur, quite often contributed by microbial activity (Sass et al. 2001). The chemoclines at the interface between the hypersaline waters of the brines and the overlaying seawater have been recognized as hot spot for microbial abundance and activity (van der Wielen et al. 2005; Daffonchio et al. 2006). Environmental gradients represent high turnover spots in the biosphere and have to be taken into account to model global biogeochemical cycles and their response to environmental changes (Brune et al. 2000).