Thermococcus aegaeicus sp. nov. and Staphylothermus hellenicus sp. nov., two novel hyperthermophilic archaea isolated from geothermally heated vents off Palaeochori Bay, Milos, Greece.

Two novel, hyperthermophilic, anaerobic, heterotrophic archaea were isolated from shallow hydrothermal vents off Palaeochori Bay, Milos, Greece. Strain P5T (BK17S6-3-b2T) is an irregular coccus, with a single polar flagellum, growing optimally at 90 degrees C, pH 6 and 2% NaCl. The DNA G+C content was 45 mol%. Due to its morphology, phylogenetic analyses based on 16S rRNA gene sequencing, DNA-DNA hybridization experiments, physiological properties and nutritional features, this strain represents a new species within the genus Thermococcus for which the name Thermococcus aegaeicus is proposed. The type strain is P5T (= DSM 12767T = JCM 10828T). Strain p8T (BK20S6-10-b1T) is a coccus that forms aggregates. It grew optimally at 85 degrees C, pH 6 and 3% NaCl. The DNA G+C content was 38 mol%. Physiological properties and sequence analysis of the 165 rRNA gene, as well as DNA-DNA hybridization experiments, indicate that this strain is a new species belonging to the genus Staphylothermus for which the name Staphylothermus hellenicus is proposed. The type strain is P8T (= DSM 12710T = JCM 10830T).