Ultrasmall epibiont Nanosynbacter lyticus strain TM7x and host bacteria transcriptional activity after initial host parasitism

Background: Oral Saccharibacteria Nanosynbacter lyticus strain TM7x lives as an ultrasmall epibiont on the surface of its host, Schaalia odontolytica strain XH001. Establishing this interaction is a poorly understood multi-step process. The recovery phase marks a shift in the TM7x/host interaction, switching from the early killing phase, with extensive host cell death, to a stable symbiosis phase where the host and epibiont can grow together. Results: Transcriptomes of TM7x and host, XH001, were captured during the recovery phase and compared to uninfected host and the early host/epibiont interaction (initial encounter). XH001 showed increased expression for rhamnose cell wall components and for the precursor to peptidoglycan while TM7x showed increases in the peptidoglycan pathway. Transporter expression was generally increased for both organisms during recovery compared to the initial encounter, though, XH001 showed lower amino acid transporter expression. Consistent with host parasitism, XH001 showed increased expression of various stress-related genes during recovery while TM7x showed reduced stress. TM7x displayed higher expression of type IV pili, consistent with increased attachment to new hosts. Conclusion: As TM7x is a member of the broadly distributed Candidate Phyla Radiation with small genomes lacking numerous biosynthetic pathways, this study provides further insights into how these epibionts interact and modulate their host bacteria.