Breznakia blatticola gen. nov. sp. nov. and Breznakia pachnodae sp. nov., two fermenting bacteria isolated from insect guts, and emended description of the family Erysipelotrichaceae

Two novel, obligately anaerobic Firmicutes from the family Erysipelotrichaceae were isolated from the intestinal tracts of a cockroach (strain ErySL, Shelfordella lateralis) and a scarab beetle larva (strain Pei061, Pachnoda ephippiata). Phylogenetic analysis indicated that the strains belong to a monophyletic group of hitherto uncultured bacteria from insect guts that are only distantly related to any described species (<90% 16S rRNA gene sequence similarity). Ultrastructural analysis revealed a Gram-positive cell envelope and, in the case of strain ErySL, a wide electron-lucent space between the cytoplasmic membrane and cell wall. In older cultures, cells formed pleomorphic rods with a thicker peptidoglycan layer. Both strains were obligately anaerobic and fermented glucose to formate, ethanol, and acetate as major products, but strain Pei061 tolerated up to 1% oxygen in the headspace. The same type of metabolism was observed with Erysipelothrix inopinata, except that the latter grew, albeit poorly, even under air. However, previous claims of a microaerophilic or facultatively anaerobic metabolism in the genus Erysipelothrix could not be substantiated. Based on phenotypic and phylogenetic evidence, we propose to classify the isolates as members of a new genus, Breznakia blatticola gen. nov. sp. nov. and Breznakia pachnodae sp. nov., with strain ErySLT (=DSM 28867T = JCM 30190T) and strain Pei061T (=DSM 16784T = JCM 30191T) as type strains, and provide an emended description of the family Erysipelotrichaceae.