A collection of 47 strains of obligately anaerobic, gram-negative, rod-shaped bacteria that were isolated mainly from spoiled beer and pitching yeast was studied to learn more about their taxonomic positions. A new species of the genus Pectinatus, Pectinatus frisingensis, a new species of the genus Selenomonas, Selenomonas lacticifex, and a new genus comprising two species, Zymophilus raffinosivorans and Zymophilus paucivorans, are described. All of the strains contained directly cross-linked meso-diaminopimelic acid-containing peptidoglycan and in addition the diamine cadaverine or (rarely) putrescine. The diamine was covalently linked to the alpha-carboxyl group of D-glutamic acid in the peptide subunit of peptidoglycan. Lipid F was also found as a characteristic cellular compound. The phylogenetic relationships of members of these new species were examined by reverse transcriptase sequencing of 16S rRNA or by DNA-DNA hybridization studies or both. All of the organisms belong to the subdivision containing species with gram-negative cell walls within the phylum of gram-positive bacteria. This finding is in good agreement with the presence of a peptidoglycan that contains diamine.