An extensive survey of the bacterial and archaeal phylogenetic diversity associated with a Paralvinella sulfincola tube and the adjacent substratum was conducted. Phylogenetic groups characterized by anaerobic and/or microaerophilic mesophiles dominated the bacterial 16S rDNA libraries (ɛ-group F, Sulfurospirillum-group, δ-Proteobacteria). The two libraries also contained groups with thermophilic lifestyles (ɛ-group D, Caldithrix-group), groups comprising species with various phenotypes (ɛ-group B, green non-sulfur bacteria), and a group without cultured representative (ɛ-group C). Archaeal 16S rDNA libraries from both samples were dominated by the novel lineage DHVE 9, and contained members of the uncultured group DHVE 3, as well as anaerobic hyperthermophiles from the families Thermofilaceae and Thermococcaceae. These results suggest the presence of mostly mesophilic and low oxygen conditions on the chimney surface, which is in accordance with descriptions of P. sulfincola's habitat conditions. Although limited by the lack of replicates, our data on the P. sulfincola tube were compared to available data on the microbial communities associated with secretions from other deep-sea vent polychaetes.