Novel bacterial and archaeal lineages from an in situ growth chamber deployed at a Mid-Atlantic Ridge hydrothermal vent

The phylogenetic diversity was determined for a microbial community obtaine d from an in situ growth chamber placed on a deep-sea hydrothermal vent on the Mid-Atlantic Ridge (23 degrees 22' N, 44 degrees 57' W). The chamber wa s deployed for 5 days, and the temperature within the chamber gradually dec reased from 70 to 20 degrees C, Upon retrieval of the chamber, the DNA was extracted and the small-subunit rRNA genes (16S rDNA) were amplified by PCR using primers specific for the Archaea or Bacteria domain and cloned. Uniq ue rDNA sequences were identified by restriction fragment length polymorphi sms, and 38 different archaeal and bacterial phylotypes were identified fro m the 85 clones screened. The majority of the archaeal sequences were affil iated with the Thermococcales (71%) and Archaeoglobales (22%) orders. A seq uence belonging to the Thermoplasmales confirms that thermoacidophiles may have escaped enrichment culturing attempts of deep-sea hydrothermal vent sa mples. Additional sequences that represented deeply rooted lineages in the low-temperature eurarchaeal (marine group II) and crenarchaeal clades were obtained. The majority of the bacterial sequences obtained mere restricted to the Aquificales (18%), the epsilon subclass of the Proteobacteria (epsil on-Proteobacteria) (40%), and the genus Desulfurobacterium (25%). Most of t he clones (28%) were confined to a monophyletic clade within the epsilon-Pr oteobacteria with no known close relatives, The prevalence of clones relate d to thermophilic microbes that use hydrogen as an electron donor and sulfu r compounds (S-0, SO4, thiosulfate) indicates the importance of hydrogen ox idation and sulfur metabolism at deep-sea hydrothermal vents. The presence of sequences that are related to sequences from hyperthermophiles, moderate thermophiles, and mesophiles suggests that the diversity obtained from thi s analysis may reflect the microbial succession that occurred in response t o the shift in temperature and possible associated changes in the chemistry of the hydrothermal fluid.