Speaker
Description
Population density greatly affects how microbes survive and grow in an environment. Porphyromonas gingivalis (Pg), a key pathogen in periodontitis disease, shows a type of growth that depends on population density. This growth suggests that there is a minimum density of Pg needed for it to survive. Interestingly, Pg is often found at low density inside the gum environment but still it survives. To explore this paradox, we combine growth experiments with mathematical models. An Alle effect model reveals a quorum threshold, below which Pg populations decline. Conditioned medium from the early colonizer Veillonella parvula (Vp) lowers this threshold, showing that these two species help each other in the early colonization stages. Adding stochastic dynamics and Fokker–Planck analysis shows that environmental factors can allow Pg to survive even below the expected threshold. Furthermore, Co-culture experiments show consistent results where small density of Pg are either saved or go extinct while Vp reaches its growth limits. A two-species game theory framework illustrates that these results explains both facilitation and competition.
Bibliography
Hussein, M., Barua, A., Qasaimeh, M. et al. Ecological and stochastic determinants of the growth and persistence of the oral pathogen Porphyromonas gingivalis. npj Syst Biol Appl (2026). https://doi.org/10.1038/s41540-026-00662-x
