Mathematical modeling predicts that CRISPR-Cas has a greater potential to benefit its plasmid in defence than in offense. Structure of the mathematical model when a CRISPR-Cas plasmid is the resident (left) or the invader plasmid (right). The authors consider seven distinct cell types: C (CRISPR-Cas bearing) and T (TA-bearing) plasmids reside in host cells; CT denotes a C cell that has been invaded by a T plasmid and vice versa; Cr* and Ci* cells have undergone segregational loss of a T plasmid, and the fate of PSK is not yet resolved; PSK cells are dead cells after post-segregational killing. When the plasmids co-reside, they are subject to basic biological parameter s (segregational loss). CRISPR-Cas and TA alter parameter s by their own modes of action x and y, respectively. Parameter f describes the positive effect PSK cells have on growth of nearby cells, where fr describes the benefit to cells containing the previously resident plasmid. All parameters adopt distinct values when their respective plasmids are resident (r) or invasive (i).
Plasmids use immune systems like #CRISPR-Cas to compete with other #plasmids, but do these systems confer an advantage? @davvi36.bsky.social &co show that CRISPR-Cas benefits resident plasmids but is constrained by toxin-antitoxin systems after horizontal transfer @plosbiology.org 🧪 plos.io/4qNbdDt