Methanocaldococcus lauensis sp. nov., a novel deep-sea hydrothermal vent hyperthermophilic methanogen

Abstract

Three hyperthermophilic methanogens, designated strain SG7T, strain SG1 and strain SLH, were isolated from the ABE and Tu’i Malila deep-sea hydrothermal vent fields along the Eastern Lau Spreading Center. Phylogenetic analysis based on 16S rRNA gene sequence indicated that strains SG7T, SG1 and SLH were affiliated with the genusMethanocaldococcuswithin the familyMethanocaldococcaceae, orderMethanococcales. They shared 95.5–99.48 % 16S rRNA gene sequence similarity to otherMethanocaldococcusspecies and were most closely related toMethanocaldococcus bathoardescens. Cells of strains SG7T, SG1 and SLH were cocci, with a diameter of 1.0–2.2 µm. The three strains grew between 45 and 93 °C (optimum, 80–85 °C), at pH 5.0–7.1 (optimum pH 6.2) and with 10–50 g l−1NaCl (optimum 20–25 g l−1). Genome analysis revealed the presence of a 5.1 kbp plasmid in strain SG7T. Based on the results of average nucleotide identity and digital DNA–DNA hybridization analyses, we propose that strains SG1 and SG7Tare representatives of a novel species, for which the nameMethanocaldococcus lauensissp. nov. is proposed; the type strain is SG7T(=DSM 109608T=JCM 39049T).