Genomic Insights into Antagonistic Coevolution: Collagen-Like Protein Expansion and Genome Plasticity in the Daphnia Parasite Pasteuria ramosa

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.