The Ultramicrobacterium Elusimicrobium minutum gen. nov., sp nov., the First Cultivated Representative of the Termite Group 1 Phylum

Insect intestinal tracts harbor several novel, deep-rooting clades of as-yet-uncultivated bacteria whose biology is typically completely unknown. Here, we report the isolation of the first representative of the termite group 1 (TG1) phylum from sterile-filtered gut homogenates of a humivorous scarab beetle larva. Strain Pei191(T) is a mesophilic, obligately anaerobic ultramicrobacterium with a gram-negative cell envelope. Cells are typically rod shaped, but cultures are pleomorphic in all growth phases (0.3 to 2.5 mu m long and 0.17 to 0.3 mu m wide). The isolate grows heterotrophically on sugars and ferments D-galactose, D-glucose, D-fructose, D-glucosamine, and N-acetyl-D-glucosamine to acetate, ethanol, hydrogen, and alanine as major products but only if amino acids are present in the medium. PCR-based screening and comparative 16S rRNA gene sequence analysis revealed that strain Pei191T belongs to the intestinal cluster, a lineage of hitherto uncultivated bacteria present in arthropod and mammalian gut systems. It is only distantly related to the previously described so-called endomicrobia lineage, which comprises mainly uncultivated endosymbionts of termite gut flagellates. We propose the name Elusimicrobium minutum gen. nov., sp. nov. (type strain, Pei191(T) = ATCC BAA-1559(T) = JCM 14958(T)) for the first isolate of this deep-branching lineage and the name Elusimicrobia phyl. nov. for the former TG1 phylum.