IADR Abstract Archives
Characterizing the Lifecycle of a Novel Saccharibacteria (TM7) Strain
Objectives: The oral cavity contains many uncultivated bacteria, including members of the Candidate Phyla Radiation (CPR). These organisms are predicted to have streamlined genomes and depend on other bacteria for nutrients/factors. Numerous efforts have been made to bring these elusive organisms in culture and we have only recently succeeded with some isolates of TM7. The goal of this study was to understand the lifecycle of one of these TM7 bacterium, HOT-955 strain PM004, which could provide valuable insights in the lifecycle of other TM7 bacteria.
Methods: PM004 requires Pseudopropionibacterium propionicum host for its growth. A 1:10 culture of P. propionicum in a modified Trypticase Soy broth (mTSBY) was infected with PM004 cells and incubated at 37°C. Samples were drawn at 4, 8, 24 and 48 hours and imaged with 16S rRNA FISH probes. 24-hour-old PM004 cells were used to infect 5 strains of closely related taxa. These new co-cultures were subcultured every 24 hours for 5 days and screened for PM004 at every passage. 24-hour-old P. propionicum and PM004 co-culture was plated on mTSBY agar plates with 5% sheep blood and incubated for 1 week. Colonies were screened for the presence of PM004 by PCR.
Results: FISH imaging showed that the number of PM004 cells increased over 24 hours and killed majority of the P. propionicum at 48 hours. PM004 infected only P. propionicum, and not any other taxa tested. When plated on mTSBY agar with blood, 80% of P. propionicum colonies were infected with PM004 showing serrated colony margins as opposed to the round colonies of uninfected P. propionicum.
Conclusions: PM004 has a reduced genome and follows a fascinating parasitic lifestyle that kills the host bacterium. Studying other strains of TM7 and CPR organisms in a similar manner, can reveal many more interesting lifecycles, and clues to allow cultivation of other CPR members.
Methods: PM004 requires Pseudopropionibacterium propionicum host for its growth. A 1:10 culture of P. propionicum in a modified Trypticase Soy broth (mTSBY) was infected with PM004 cells and incubated at 37°C. Samples were drawn at 4, 8, 24 and 48 hours and imaged with 16S rRNA FISH probes. 24-hour-old PM004 cells were used to infect 5 strains of closely related taxa. These new co-cultures were subcultured every 24 hours for 5 days and screened for PM004 at every passage. 24-hour-old P. propionicum and PM004 co-culture was plated on mTSBY agar plates with 5% sheep blood and incubated for 1 week. Colonies were screened for the presence of PM004 by PCR.
Results: FISH imaging showed that the number of PM004 cells increased over 24 hours and killed majority of the P. propionicum at 48 hours. PM004 infected only P. propionicum, and not any other taxa tested. When plated on mTSBY agar with blood, 80% of P. propionicum colonies were infected with PM004 showing serrated colony margins as opposed to the round colonies of uninfected P. propionicum.
Conclusions: PM004 has a reduced genome and follows a fascinating parasitic lifestyle that kills the host bacterium. Studying other strains of TM7 and CPR organisms in a similar manner, can reveal many more interesting lifecycles, and clues to allow cultivation of other CPR members.