sp. nov., a moderately thermophilic methanotroph of the family isolated from a deep-sea hydrothermal field.

A novel aerobic methanotrophic bacterium, designated as strain IN45, was isolated from colonisation systems deployed at the Iheya North deep-sea hydrothermal field in the mid-Okinawa Trough. IN45 was a moderately thermophilic obligate methanotroph that grew only on methane or methanol at temperatures between 25 and 56 °C (optimum 45-50 °C). It was an oval-shaped, Gram-reaction-negative, motile bacterium with a single polar flagellum and an intracytoplasmic membrane system. It required 1.5-4.0 % (w/v) NaCl (optimum 2-3 %) for growth. The major phospholipid fatty acids were Cω7, C and Cω7. The major isoprenoid quinone was Q-8. The 16S rRNA gene sequence comparison revealed 99.1 % sequence identity with IT-9, the only species of the genus with a validly published name within the family . The complete genome sequence of IN45 consisted of a 2.42-Mbp chromosome (DNA G+C content, 64.1 mol%) and a 20.5-kbp plasmid. The genome encodes genes for particulate methane monooxygenase and two types of methanol dehydrogenase ( and ). Genes involved in the ribulose monophosphate pathway for carbon assimilation are encoded, but the transaldolase gene was not found. The genome indicated that IN45 performs partial denitrification of nitrate to NO, and its occurrence was indirectly confirmed by NO production in cultures grown with nitrate. Genomic relatedness indices between the complete genome sequences of IN45 and IT-9, such as digital DNA-DNA hybridisation (51.2 %), average nucleotide identity (92.94 %) and average amino acid identity (93.21 %), indicated that these two methanotrophs should be separated at the species level. On the basis of these results, strain IN45 represents a novel species, for which we propose the name sp. nov. with IN45 (=JCM 35101 =DSM 113422) as the type strain.