Figure 3.

The cause of the persistent coexistence of phages and bacteria in the intestinal tract. ① The distribution of bacteriophages and bacteria is spatially heterogeneous. There are no phages in the intestinal villi, few phages in the intestinal mucosa, and a large number of phages in the intestinal lumen. The phage density in the intestinal tract presents a mucosal-lumenal gradient, providing a place for bacteria to avoid phage attack. ② The specific interaction between phages and bacteria, the competition between defense and anti-defense systems, and the way in which genes are shared to form new mutations or new species promote coevolution.