Phages are key drivers of genomic diversity in bacterial
populations as they impose strong selective pressure on the
evolution of bacterial defense mechanisms across closely
related strains. The pan-immunity model suggests that such
diversity is maintained because the effective immune system of
a bacterial species is the one distributed across all strains
present in the community. However, only few studies have
analyzed the distribution of bacterial defense systems at the
community-level, mostly focusing on CRISPR and comparing
samples from complex environments. Here, we studied 27
cheese-associated species encompassing 2'778 bacterial
genomes and 158 metagenomes, which are dominated by a few
bacterial taxa and occur in relatively stable environments.