A novel haloarchaeal-related lineage is widely distributed in deep oceanicregions

During our study of the 16S rRNA gene sequence-based archaeal diversity of a deep-sea site located at a 3000 m depth at the Antarctic Polar Front, we detected several phylotypes ascribed to already known Group II and III Eury archaeota, and a cluster of distinct sequences that branched off at the bas e of haloarchaea. The position of this lineage (marine Group IV) was very r obust using distance (neighbour-joining) and maximum-likelihood methods. Su bsequently, we designed specific primers for the detection of this archaeal group in other marine environments using polymerase chain reaction amplifi cation and sequence comparison. Group IV archaea were found in the Antarcti c area (across a gradient from the Southern ocean to the South Atlantic), a nd also in North Atlantic and Mediterranean waters. In all oceanic location s, Group IV archaea were never detected in surface waters, but were vertica lly distributed in the deepest part of the water column.