Pelolinea submarina gen. nov., sp. nov., an anaerobic, filamentous bacterium of the phylum Chloroflexi isolated from subseafloor sediment , was isolated from a methanogenic community, which was originally established from subseafloor sediments collected from off the Shimokita Peninsula, Japan. Cells were non-spore-forming, non-motile, Gram-stain-negative and filamentous. The filaments were longer than 10 mm and 130-150 nm in width. Growth of the strain was observed at 10-37 6C (optimum 25-30 6C), at pH 5.5-8.5 (optimum pH 7.0) and in 0-50 g NaCl l "1 (optimum 15 g NaCl l "1 ). The strain was able to grow with a number of carbohydrates in the presence of yeast extract. The major cellular fatty acids were monounsaturated C 18 : 1 v9, C 16 : 1 v7 and saturated C 18 : 0 and C 16 : 0 . The intact polar lipids of the strain were dominated by diacylglyceride and sphingolipid core lipid structures with monoglycosidic, mixed phosphomonoglycosidic and fatty-acid-modified monoglycosidic polar head groups. The G+C content of the genomic DNA was 52.4 mol%. Based on the comparative 16S rRNA gene sequence analysis, strain MO-CFX1T was affiliated with the class Anaerolineae within the phylum Chloroflexi and was most closely related to Leptolinea tardivitalis YMTK-2 T (sequence identity of 91.0 %). Based on phenotypic and genetic properties of the novel isolate, we propose a novel species representing a new genus Pelolinea submarina gen. nov., sp. nov., for strain MO-CFX1 T (5JCM 17238 T ,5KCTC 5975 T ). This is the first formal description, to our knowledge, of an isolate of the phylum Chloroflexi from the deep-sea sedimentary environment.Culture-independent molecular studies based on a survey of PCR-amplified 16S rRNA genes have revealed members of the bacterial phylum Chloroflexi to be one of the dominant bacterial components in subseafloor sedimentary environments (Blazejak & Schippers, 2010;Fry et al., 2008;Inagaki et al., 2006;Inagaki & Nakagawa, 2008;Teske, 2013;Yamada & Sekiguchi, 2009). Most of the 16S rRNA gene sequences of members of the phylum Chloroflexi belong to members of the classes Anaerolineae, Caldilineae and Dehalococcoidia. These findings strongly indicate that members of the phylum Chloroflexi play an important role in biogeochemical cycles in the marine subsurface environment. However, until now, cultured representatives from these environments have not been available and their detailed physiological, genetic and ecological properties are currently not well understood.Recently, we have successfully isolated micro-organisms of the class Anaerolineae, designated strains MO-CFX1 T and MO-CFX2, from marine subsurface sediments collected from off the Shimokita Peninsula of Japan in the northwestern Pacific Ocean (Site C9001, 1180 m water depth) (Imachi et al., 2011). Enrichment and isolation of these strains were achieved using a continuous-flow bioreactor Abbreviations: BSTFA, N,O-Bis(trimethylsilyl)trifluoroacetamide; FAME, fatty acid methyl ester; IPL, intact polar lipid; TLE, total lipid extract.