Polycladomyces abyssicola gen. nov., sp. nov., a thermophilic filamentous bacterium isolated from hemipelagic sediment

Abstract

A novel filamentous bacterium, designated strain JIR-001T, was isolated from hemipelagic sediment in deep seawater. This strain was non-motile, Gram-positive, aerobic, heterotrophic and thermophilic; colonies were of infinite form and ivory coloured with wrinkles between the centre and the edge of the colony on ISP2 medium. The isolate grew aerobically at 55–73 °C with the formation of aerial mycelia; spores were produced singly along the aerial mycelium. These morphological features show some similarities to those of the type strains of some species belonging to the family Thermoactinomycetaceae . Phylogenetic analysis based on 16S rRNA gene sequences confirmed that strain JIR-001T belongs to the family Thermoactinomycetaceae within the class Bacilli . Similarity levels between the 16S rRNA gene sequence of strain JIR-001T and those of the type strains of Thermoactinomycetaceae species were 85.5–93.5 %; highest sequence similarity was with Melghirimyces algeriensis NariEXT. In the DNA–DNA hybridization assays between strain JIR-001T and its phylogenetic neighbours the mean hybridization levels with Melghirimyces algeriensis NariEXT, Planifilum fimeticola H0165T, Planifilum fulgidum 500275T and Planifilum yunnanense LA5T were 5.3–7.5, 2.3–4.7, 2.1–4.8 and 2.5–4.9 %, respectively. The DNA G+C content of strain JIR-001T was 55.1 mol%. The major fatty acids were iso-C15 : 0, iso-C17 : 0, iso-C16 : 0 and C16 : 0. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylglycerol, glucolipid, phosphatidylserine, an amino-group containing phospholipid, an unknown phospholipid and two unknown lipids. The predominant menaquinone was MK-7 and the cell-wall peptidoglycan contained meso-diaminopimelic acid, glutamic acid and alanine. On the basis of phenotypic characteristics and 16S rRNA gene sequence comparisons, strain JIR-001T is considered to represent a novel species in a new genus of the family Thermoactinomycetaceae , for which the name Polycladomyces abyssicola gen. nov., sp. nov. is proposed. The type strain of Polycladomyces abyssicola is JIR-001T ( = JCM 18147T = CECT 8074T).