Seven bacterial strains capable of oxidizing methyl sulfides were isolated from experimental biofilters filled with tree-bark compost. The isolates could be divided into two groups according to their method of methyl sulfide degradation. Four isolates could use only dimethyl disulfide as the sole source of energy and three strains were able to use dimethyl sulfide and dimethyl disulfide. Oxidation of the methyl sulfides by both groups led to the stoichiometric formation of sulfate. Chemotaxonomic, morphological, physiological and phylogenetic properties identified all isolates as members of the genus Pseudonocardia. The absence of phosphatidylcholine from the polar lipid pattern, as well as results of 16S rDNA analyses, led to the proposal of two new species, Pseudonocardia asaccharolytica sp. nov. and Pseudonocardia sulfidoxydans sp. nov. The type strains are P. asaccharolytica DSM 44247T and P. sulfidoxydans DSM 44248T. With respect to the characteristic polar lipid pattern and the ability to oxidize sulfides, an emended description of the genus Pseudonocardia is proposed.