In situ analysis of phototrophic sulfur bacteria in the chemocline of meromictic Lake Cadagno (Switzerland)

Comparative sequence analysis of a 16S rRNA gene clone library from the che mocline of the meromictic Lake Cadagno (Switzerland) revealed the presence of a diverse number of phototrophic sulfur bacteria. Sequences resembled th ose of rRNA of type strains Chromatium okenii DSM169 and Amoebobacter purpu reus DSM4197, as well as those of four bacteria forming a tight cluster wit h A. purpureus DSM4197 and Lamprocystis roseopersicina DSM229. In situ hybr idization with fluorescent (Cy3 labeled) oligonucleotide probes indicated t hat all large-celled phototrophic sulfur bacteria in the chemocline of Lake Cadagno were represented by C. okenii DSM169, while small-celled phototrop hic sulfur bacteria consisted of four major populations with different dist ribution profiles in the chemocline indicating different ecophysiological a daptations.