Clone size statistics of tumor-inhabiting bacteria

Bacteria inhabit different areas of the human body and perform essential functions. Increasing evidence of bacterial effects on cancer progression has brought interest to tumor-inhabiting bacteria. However, it is not understood how bacteria affect the tumor, nor how the tumor environment affects bacterial dynamics. Recent experiments, done with barcoded bacterial colonies, show that clone sizes of bacteria inhabiting tumors in mice exhibit universal statistical patterns. The patterns are robust across experiments and collection times, and unique to bacteria grown in the tumor environment rather than in liquid culture. We find that the liquid experiments can be explained by a simple birth-death process that cannot capture the observed statistics in the tumor. In this work, we develop a mechanistic understanding of the microecological dynamics of tumor-inhabiting bacteria. We present a physical model that captures the observed statistics with simple assumptions and explains the uniqueness of this observation to the tumor environment.