Tuz Lake is an inland thalassohaline water body located in central Anatolia that contributes to 60% of the total salt production in Turkey per year. The microbiota inhabiting this lake has been studied by FISH, denaturing gradient gel electrophoresis of PCR-amplified fragments of 16S rRNA genes, and 16S rRNA gene clone library analysis. Total cell counts per milliliter (1.38 x 10(7)) were in the range of the values normally found for hypersaline environments. The proportion of Bacteria to Archaea in the community detectable by FISH was one to three. 16S rRNA gene clone libraries indicated that the archaeal assemblage was dominated by members of the Square Haloarchaea of the Walsby group, although some other groups were also found. Bacteria were dominated by members of the Bacteroidetes, including Salinibacter ruber-related phylotypes. Because members of Bacteroidetes are widely present in different hypersaline environments, a phylogenetic analysis of 16S rRNA gene sequences from Bacteroidetes retrieved from these environments was carried out in order to ascertain whether they formed a unique cluster. Sequences retrieved from Tuz Lake and a group of sequences from other hypersaline environments clustered together in a branch that could be considered as the 'halophilic branch' within the Bacteroidetes phylum.