Seven unidentified strictly anaerobic, Gram-negative, non-spore-forming bacteria from spoiled beer or the brewery environment were characterized. Based on 16S rRNA gene sequence analyses, all strains were affiliated to the Sporomusa sub-branch of the class 'Clostridia'. Three of the strains were non-motile cocci, on average 1.5 x 1.2 microm or 1.2 x 1.0 microm, occurring mainly singly or in pairs. They shared nearly identical (>99 %) 16S rRNA gene sequences, being most closely related to the species of the Megasphaera-Anaeroglobus group (< or =93.9 % similarity). According to DNA-DNA hybridization results, the coccoid strains represented two genospecies, neither of which was related to any of the recognized Megasphaera species. Several phenotypic characteristics and/or DNA G+C content also differentiated the strains from each other and from their closest relatives. The other four novel strains were motile, slightly curved to helical rods, 0.6-0.8 x 3-50 microm or more in size. They shared identical 16S rRNA gene sequences and ribofragment patterns. The highest 16S rRNA gene similarity was found between these isolates and Pectinatus cerevisiiphilus ATCC 29359T (95.6 %) and Pectinatus frisingensis ATCC 33332T (93.6 %). The novel strains also differed from recognized Pectinatus species in their sugar utilization, proteolytic activity, catalase activity, antibiotic resistance and temperature tolerance. The results suggest that the bacteria belong to three novel species, for which the names Megasphaera paucivorans sp. nov. (type strain VTT E-032341T = DSM 16981T), Megasphaera sueciensis sp. nov. (type strain VTT E-97791T = DSM 17042T) and Pectinatus haikarae sp. nov. (type strain VTT E-88329T = DSM 16980T) are proposed.