A Gram-negative, strictly aerobic and heterotrophic, non-spore-forming bacterial strain, designated LM22(T), was isolated from activated sludge of a sequencing batch reactor for the treatment of malachite green effluent. Cells of strain LM22(T) were slightly curved to straight rods (0.3-0.5��0.6-1.0�gm) and motile by a single polar flagellum. Strain LM22(T) was negative for oxidase and catalase activities and phototrophic growth. An internal membrane system and bacteriochlorophyll a were absent. Growth occurred at 20-40�XC (optimum 30-35�XC) and pH6.0-10.0 (optimum pH7.0-7.5). Strain LM22(T) did not require NaCl for growth and tolerated up to 2.0 % NaCl (optimum 0.5 %). The major ubiquinone was Q-10. The major fatty acids (>10 % of the total) were C(18 : 1)�s7c (32.9 %), C(19 : 0) cyclo �s8c (18.7 %), C(16 : 0) (12.1 %) and C(16 : 0) 2-OH (10.5 %). Phylogenetic analysis of 16S rRNA gene sequences showed that Inquilinus limosus AU0476(T) was the closest relative (90.4 % 16S rRNA gene sequence similarity). The DNA G+C content was 65.6 mol%. On basis of phenotypic, chemotaxonomic and phylogenetic data, strain LM22(T) was considered to represent a novel genus and species of the family Rhodospirillaceae, for which the name Dongia mobilis gen. nov., sp. nov. is proposed. The type strain of Dongia mobilis is LM22(T) (=CGMCC 1.7660(T) =JCM 15798(T)).