The microflora developing during a continuous enrichment culture from a hydrothermal chimney sample was investigated by molecular methods. The culture was performed in a gas-lift bioreactor under anaerobic conditions, at 90 degrees C and pH 6.5, on a complex medium containing sulfur as the terminal electron acceptor. Archaeal and bacterial diversity was studied. Microorganisms affiliated with the genera Pyrococcus, Marinitoga, and Bacillus were detected through DGGE analysis of 16S rDNA. Additional sequences phylogenetically related to Thermococus and epsilon-Proteobacteria were detected by cloning and sequencing of 16S rDNA from two samples of the enrichment culture. In comparison, the sequences retrieved from cloning analysis from an enrichment culture performed in a flask (batch condition) using the same Culture medium showed that only members of the genus Thermococcus were cultivated. Therefore, continuous enrichment culture using the gas-lift bioreactor can be considered as an efficient and improved method for investigating microbial communities originating from deep-sea hydrothermal vents.