Evolution of antivirus defense in prokaryotes, depending on the environmental virus prevalence and virome dynamics

The virus-host arms race is a major component of the evolutionary process in all organisms that drove the evolution of a broad variety of immune mechanisms. In the last few years, over 200 distinct antivirus defense systems have been discovered in prokaryotes. There are two major modes of immunity acquisition: innate immune systems spread through microbial populations via HGT, whereas adaptive-type immune systems acquire immunity via direct interaction with the virus. We developed a mathematical model to explore the short-term evolution of prokaryotic immunity and showed that in stable environments with predictable viral repertoires, adaptive-type immunity is the optimal defense strategy, whereas in fluctuating environments with unpredictable virus composition, HGT dominates the immune landscape.