Clade G6 Saccharibacteria ("Ca. Nanogingivalaceae") are Highly Divergent From Clade G1

Objectives: Saccharibacteria have reduced genomes, a small cell size, and appear have a parasitic lifestyle, dependent on host bacteria. At least 6 highly diverse clades of Saccharibacteria inhabit the human oral cavity. However, all oral Saccharibacteria with currently available complete genomes or cultured isolates belong to the clade, G1, leaving clades G2-G6 poorly understood.
Methods: Nanopore sequencing was used to deliver the first complete genome of an oral Saccharibacteria outside of clade G1, the G6 (proposed name, “Ca. Nanogingivalaceae”) taxon, JB001.
Results: Phylogenomic and pangenomic analysis showed that G6 Saccharibateria are quite divergent from the more well-understood G1 taxa, and encode a distinct functional and metabolic repertoire.
Conclusions: These results indicate that G6 Saccharibacteria may have unique lifestyles, and depend on their hosts to fulfill rather different metabolic requirements. If true, this would likely have significant implications regarding the evolution, ecological role, and impact on human health of clade G6 Saccharibacteria.