Ectopical expression of bacterial collagen-like protein supports its role as adhesin in host-parasite coevolution

For a profound understanding of antagonistic coevolution, it is necessary
to identify the coevolving genes. The bacterium Pasteuria and its host,
the microcrustacean Daphnia, are a well-characterized paradigm for
co-evolution, but the underlying genes remain largely unknown. A
genome-wide association study suggested a Pasteuria collagen-like protein
7 (Pcl7) as a candidate mediating parasite attachment and driving its
coevolution with the host. Since Pasteuria ramosa cannot currently be
genetically manipulated, we used Bacillus thuringiensis to express a
fusion protein of a Pcl7 carboxy- terminus from P. ramosa and the
amino-terminal domain of a B. thuringiensis collagen-like protein (CLP).
Mutant B. thuringiensis (Pcl7-Bt) spores but not wild-type B.
thuringiensis (WT-Bt) spores, attached to the same site of susceptible
hosts as P. ramosa. Furthermore, Pcl7-Bt spores attached readily to
susceptible host genotypes, but only slightly to resistant host genotypes.
These findings indicated that the fusion protein was properly expressed
and folded and demonstrated that indeed the C-terminus of Pcl7 mediates
attachment in a host genotype-specific manner. These results provide
strong evidence for the involvement of a CLP in the coevolution of Daphnia
and P. ramosa and open new avenues for genetic epidemiological studies of
host–parasite interactions.