An extremely halophilic archaeon was isolated from a sample of the brine–sediment interface of the Shaban Deep in the northern Red Sea. Phylogenetic analysis of the 16S rRNA gene sequence revealed a close proximity to Halorhabdus utahensis (99.3 %), the sole species of the genus Halorhabdus. Strain SARL4BT formed non-pigmented colonies and showed optimum growth at 45 °C, in 27 % (w/v) NaCl and at pH 6.5–7.0. This organism utilized a few complex substrates, such as yeast extract and starch, for growth. Strain SARL4BT grew under anaerobic and microaerophilic conditions but grew extremely poorly under aerobic conditions. The ether lipids were diphytanyl derivatives. The DNA G+C content of the type strain was 61.7 mol%. On the basis of the phylogenetic data and physiological and biochemical characteristics, strain SARL4BT represents a novel species of the genus Halorhabdus, for which the name Halorhabdus tiamatea is proposed. The type strain is SARL4BT (=DSM 18392T=JCM 14471T). An emended description of the genus Halorhabdus is also proposed.
A novel methane-producing archaeon, strain NOBI-1T was isolated from an anaerobic, propionate-degradation enrichment culture, which was originally obtained from a mesophilic methanogenic sludge digesting municipal sewage sludge. Cells were non-motile, rod-shaped, 0.7–1.0 μm by 2.0 μm, and formed multicellular filaments longer than 8 μm. Growth was observed between 35 and 55 °C (optimum 50 °C) and pH 6.7 and 8.0 (optimum pH 7.0). The G+C content of the genomic DNA was 56.3 mol%. The strain utilized H2 and formate for growth and methane production. Based on comparative sequence analyses of the 16S rRNA gene and mcrA gene (encoding the alpha subunit of methyl-coenzyme M reductase, a key enzyme in the methane-production pathway), strain NOBI-1T was affiliated with the order Methanomicrobiales, but it was significantly distant from any other known species within the order. The most closely related species based on 16S rRNA and mcrA gene sequence similarity were respectively ‘Candidatus Methanoregula boonei’ (93.7 % 16S rRNA gene sequence similarity) and Methanocorpusculum parvum (74.2 % deduced McrA amino acid sequence similarity to the type strain). These phenotypic and genetic properties justified the creation of a novel species of a new genus for the strain, for which we propose the name Methanolinea tarda gen. nov., sp. nov. The type strain of Methanolinea tarda is strain NOBI-1T (=DSM 16494T =JCM 12467T =NBRC 102358T).