Single Cell Genomics of Uncultured, Health-associated Tannerella BU063 (Oral Taxon 286) and Comparison to the Closely Related Pathogen Tannerella Forsythia

The uncultivated bacterium Tannerella BU063 (oral taxon 286) is the closest relative to the periodontal pathogen Tannerella forsythia, but is not disease-associated itself. Using a single cell genomics approach, we isolated 12 individual BU063 cells by flow cytometry, and we amplified and sequenced their genomes. Comparative analyses of the assembled genomic scaffolds and their gene contents allowed us to study the diversity of this taxon within the oral community of a single human donor that provided the sample. Eight different BU063 genotypes were represented, all about 5% divergent at the nucleotide level. There were 2 pairs of cells and one group of three that were more highly identical, and may represent clonal populations. We did pooled assemblies on the nearly identical genomes to increase the assembled genomic coverage. The presence of a set of 66 "core" housekeeping genes showed that two of the single cell assemblies and the assembly derived from the three putatively identical cells were essentially complete. As expected, the genome of BU063 is more similar to Tannerella forsythia than any other known genome, although there are significant differences, including a 44% difference in gene content, changes in metabolic pathways, loss of synteny, and an 8-9% difference in GC content. Several identified virulence genes of T. forsythia are not found in BU063 including karilysin, prtH, and bspA. The absence of these genes may explain the lack of periodontal pathogenesis by this species and provides a new foundation to further understand the genome evolution and mechanisms of bacterial-host interaction in closely related oral microbes with different pathogenicity potential.