Genomic insights into antagonistic coevolution: collagen-like protein expansion and genome plasticity in the <i>Daphnia</i> parasite <i>Pasteuria ramosa</i>

Collagen-like proteins (CLP) serve many pathogenic bacteria as adhesins to attach to host tissue. It was suggested that CLPs are a major determinant in the coevolution of the model system Daphnia (Crustacean) and its virulent pathogen Pasteuria ramosa (Bacillota). We analyzed 5 new high-quality genomes of P. ramosa originating from three host species. CLP genes underwent a radiation in P. ramosa. Genome comparison showed a high synteny, with few structural variations, mainly involving CLPs and transposases, both of which underwent recent multiplications. While most CLP genes are conserved, the presence/absence of some CLP genes varies among isolates. Our findings suggest a rapid radiation of CLP genes. These observations, derived from the first published genomes of P. ramosa, are consistent with the notion of rapid Pasteuria-Daphnia coevolution, as previously suggested for this highly specific host-parasite system.