ABSTRACT. – A novel chemoorganotrophic, non spore forming bacterium with a cell size of 2.3 ± 0.3 μm long and 1.0 ± 0.1 μm wide was isolated from aquifer water in the Cévennes mountains, France. Cells of the isolate, designated strain LMB64^T, were motile, straight rods with a single polar flagellum, and are able to accumulate poly-β-hydroxybutyrate granules. Growth was observed at temperatures between 14 and 45°C (optimum 30°C) and pH between 6·0 and 8·0 (optimum pH = 6·0). NaCl was not required for growth. Catalase, oxidase and arginine dihydrolase activities and indole production were detected. The major cellular fatty acids were C_16:0 and C_16:1 ω7c or/and C_16:1 ω6c (40.1 and 36.2 %, respectively). The predominant respiratory quinone was ubiquinone 8 (Q-8), but another dominant compound, which did not elute with Q8 or any documented quinone, was observed. The G+C content of the genomic DNA was 64.2 mol %. A phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain LMB64T forms a distinct lineage within the family Neisseriaceae of the β-Proteobacteria class. The strain LMB64T appears closely related to Pseudogulbenkiania subflava^T (95.7 % 16S rRNA gene sequence similarity), Gulbenkiania mobilis^T (94.7 %) and Paludibacterium yongneupense^T (94.6 %). On the basis of its physiological and molecular properties, the strain LMB64^T (= CNCM I-4290) is proposed as the type strain of Aquaphilus dolomiae gen. nov., sp. nov.