ABSTRACT It is generally assumed that hypersaline environments with sodium chloride concentrations close to saturation are dominated by halophilic members of the domain Archaea , while Bacteria are not considered to be relevant in this kind of environment. Here, we report the high abundance and growth of a new group of hitherto-uncultured Bacteria in crystallizer ponds (salinity, from 30 to 37%) from multipond solar salterns. In the present study, these Bacteria constituted from 5 to 25% of the total prokaryotic community and were affiliated with the Cytophaga-Flavobacterium-Bacteroides phylum. Growth was demonstrated in saturated NaCl. A provisional classification of this new bacterial group as “ Candidatus Salinibacter gen. nov.” is proposed. The perception that Archaea are the only ecologically relevant prokaryotes in hypersaline aquatic environments should be revised.