Summary auto-generated
This study describes the isolation and characterization of two novel hyperthermophilic archaeal species from geothermally heated marine sediments off Palaeochori Bay, Milos, Greece. Strain P5T, an irregular coccus with a single polar flagellum, grows optimally at 90°C, pH 6, and 2% NaCl, with a DNA G+C content of 45 mol%. Phylogenetic analysis of 16S rRNA sequences and DNA-DNA hybridization place it within genus Thermococcus, designated Thermococcus aegaeicus. Strain P8T, a coccus forming large aggregates, grows optimally at 85°C, pH 6, and 3% NaCl, with DNA G+C content of 38 mol%. Phylogenetic analysis places it within genus Staphylothermus, designated Staphylothermus hellenicus. Both organisms are obligate anaerobes that utilize organic compounds as carbon sources and require elemental sulfur for growth. DNA-DNA hybridization values below 70% with their closest known relatives confirm their status as distinct species. These findings expand understanding of archaeal diversity in Aegean hydrothermal vent systems.
Key findings
- Two novel hyperthermophilic archaeal species isolated from Milos hydrothermal vents: Thermococcus aegaeicus (optimal growth 90°C) and Staphylothermus hellenicus (optimal growth 85°C)
- Thermococcus aegaeicus has a unique monopolar flagellum and 45 mol% G+C content; distinguished from related species by starch utilization and inability to utilize casein
- Staphylothermus hellenicus can tolerate higher NaCl concentrations (2-8%) than related S. marinus, representing adaptation to high salt ecosystem
- DNA-DNA hybridization values of 47% and 38.5% for T. aegaeicus and 37.5% for S. hellenicus with closest relatives confirm distinct species status
- Both strains are obligate anaerobes that require elemental sulfur as electron acceptor and utilize complex organic substrates rather than simple carbohydrates
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Abstract
Two novel, hyperthermophilic, anaerobic, heterotrophic archaea were isolated from shallow hydrothermal vents off Palaeochori Bay, Milos, Greece. Strain P5(T) (BK17S6-3-b2(T)) 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 P5(T) (=DSM 12767(T)=JCM 10828(T)). Strain P8(T) (BK20S6-10-b1(T)) 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 16S 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 P8(T) (=DSM 12710(T)=JCM 10830(T)).