Many environmental and genetic factors can influence the mode and tempo of bacteria-phage coevolution. In microbial communities acquisition of mobile genetic elements such as plasmids is an important yet disruptive process for bacterial populations. Using experimental evolution we investigate how antagonistic coevolution between the bacteria, Pseudomonas fluorescens, and phage, SBW252 shapes, and in turn is shaped by the presence of a large conjugative plasmid, pQBR103.
We find that bacteria-phage coevolution can drive the extinction of plasmid from bacterial populations when plasmids are not under positive selection, limiting the existence conditions for these important vectors of horizontal gene transfer. Under selection for plasmid bound traits however, plasmid carriage altered the rate and trajectory of bacteria-phage coevolution; bacteria and phage evolved lower resistance and infectivity respectively and bacteria evolved high rates of mucoidy, a form of weak phage resistance. Gene expression data suggests that that subtle effects on bacterial regulation due to plasmid carriage ‘primes’ the bacteria towards this evolutionary path. Our findings demonstrate how species interactions can have evolutionary consequences for bacteria beyond those observed in simple pairwise interactions.