An aerobic, alkane-oxidizing bacterium, designated strain EPR92(T), was isolated from hydrothermal fluids that had been collected from a deep-sea vent on the East Pacific Rise (at 9° 50' N 104° 17' W). The cells of the novel strain were Gram-staining-negative rods that measured approximately 1.4 µm in length and 0.4 µm in width. Strain EPR92(T) grew at 20-40 °C (optimum 35 °C), with1.0-5.0% (w/v) NaCl (optimum 2.5%), and at pH 4.0-8.5 (optimum pH 7.5). The generation time under optimal conditions was 63 min. Strain EPR92(T) grew aerobically in artificial seawater minimal medium with n-alkanes as sole carbon and energy sources, and also in artificial seawater medium supplemented with peptone and yeast extract. The predominant fatty acids were C(18:1)ω7c, C(19:0) cyclo ω8c, 11-methyl C(18:1)ω7c and a putative C(12:0) aldehyde. The major polar lipids were phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine and four unidentified aminolipids. The major respiratory quinone was Q-10 and the genomic DNA G+C content was 60.7 mol%. Phylogenetic analyses of the 16S rRNA gene showed that strain EPR92(T) belongs in the class Alphaproteobacteria and the recognized species that were most closely related to the novel strain were identified as Parvibaculum indicum P-31(T) (98.7% sequence similarity) and Parvibaculum lavamentivorans DS-1(T) (95.8%). In DNA-DNA hybridizations, the level of DNA-DNA relatedness observed between strain EPR92(T) and P. indicum P-31(T) was 47.7%, indicating that the two strains do not belong to the same species. Based on the phylogenetic, physiological, chemotaxonomic and genetic evidence, strain EPR92(T) represents a novel species within the genus Parvibaculum, for which the name Parvibaculum hydrocarboniclasticum sp. nov. is proposed. The type strain is EPR92(T) ( = DSM 23209 = JCM 16666(T)).