A novel moderately thermophilic, heterotrophic anaerobe, designated strain LG1(T), was isolated from the Mariner deep-sea hydrothermal vent field along the Eastern Lau Spreading Center and Valu Fa Ridge. Cells of strain LG1(T) were motile rods, occurring singly or in pairs, 0.6 mu m in width and 1.2 mu m in length. The strain LG1(T) grew between 40 and 70 degrees C (optimum 50-55 degrees C), at a pH between 5 and 8 (optimum pH 6.5) and with 7.5-50 g L-1 NaCl (optimum 30 g L-1). Sulfur, cystine and thiosulfate were reduced to sulfide, and cell yield was improved in the presence of cystine. Strain LG1(T) was an organotroph able to use a variety of organic compounds. Phylogenetic analysis based on 16S rRNA gene sequence comparisons indicated that strain LG1(T) was affiliated to the genus Marinitoga within the order Petrotogales. It shared 95.34-96.31% 16S rRNA gene sequence similarity with strains of other Marinitoga species, and is most closely related to Marinitoga okinawensis. Genome analysis revealed the presence of a prophage sharing high sequence homology with the viruses MPV1, MCV1 and MCV2 hosted by Marinitoga strains. Based on the data from the phylogenetic analyses and the physiological properties of the novel isolate, we propose that strain LG1(T) is a representative of a novel species, for which the name Marinitoga lauensis sp. nov. is proposed; the type strain is LG1(T) (=DSM 106824 = JCM 32613). (C) 2019 Elsevier GmbH. All rights reserved.