Distribution and diversity of sulfur-oxidizing Thiomicrospira spp. at a shallow-water hydrothermal vent in the Aegean Sea (Milos, Greece)

A shallow-water hydrothermal vent system in the Aegean Sea close to the isl and of Miles (Greece) was chosen to study the diversity and distribution of the chemolithoautotrophic sulfur-oxidizing bacterium Thiomicrospira. Cell numbers in samples from different regions around a solitary vent decreased toward the center of the vent (horizontal distribution), as well as with de pth (vertical distribution), corresponding to an increase in temperature (f rom ca. 25 to 60 degrees C) and a decrease in pH (from ca. pH 7 to 5). Thio microspira was one of the most abundant culturable sulfur oxidizers and was even dominant in one region. Phylogenetic analysis of Thiomicrospira spp. present in the highest most-probable-number (MPN) dilutions revealed that m ost of the obtained sequences grouped in two new closely related clusters w ithin the Thiomicrospira branch. Two different new isolates, i.e., Milos-T1 and Milos-T2, were obtained from high-dilution (10(-5)) enrichments. Phylo genetic analysis indicated that isolate Milos-T1 is related to the recently described Thiomicrospira kuenenii and Hydrogenovibrio marinus, whereas iso late Milos-T2 grouped with the MPN sequences of cluster 2. The predominance of strain Milos-T2 was indicated by its identification in several environm ental samples by hybridization analysis of denaturing gradient gel electrop horesis (DGGE) patterns and by sequencing of one of the corresponding bands , i.e., ML-1, from the DGGE gel. The results shown in this paper support ea rlier indications that Thiomicrospira species are important members of hydr othermal vent communities.