Pasteuria spp. belong to a group of genetically diverse endospore-forming bacteria (phylum: Firmicutes) that are known to parasitize plant-parasitic nematodes and water fleas (Daphnia spp.). Collagen-like fibres form the nap on the surface of endospores and the genes encoding these sequences have been hypothesised to be involved in the adhesion of the endospores of Pasteuria spp. to their hosts. We report a group of 17 unique collagen-like genes putatively encoded by Pasteuria penetrans (strain: Res148) that formed five different phylogenetic clusters and suggest that collagen-like proteins are an important source of genetic diversity in animal pathogenic Firmicutes including Pasteuria. Additionally, and unexpectedly, we identified a putative collagen-like sequence which had a very different sequence structure to the other collagen-like proteins but was similar to the protein sequences in Megaviruses that are involved in host-parasite interactions. We, therefore, suggest that these diverse endospore surface proteins in Pasteuria are involved in biological functions, such as cellular adhesion; however, they are not of monophyletic origin and were possibly obtained de novo by mutation or possibly through selection acting upon several historic horizontal gene transfer events.
Aims: Phytonematodes are a constraint on crop production and have been controlled using nematicides; these are highly toxic and legislation in Europe and elsewhere is prohibiting their use and alternatives are being sought. Pasteuria penetrans is a hyperparasitic bacterium that form endospores and have potential to control root-knot nematodes (Meloidogyne spp.), but their attachment to the nematode cuticle is hostspecific. Understanding host specificity has relied upon endospore inhibition bioassays using immunological and biochemical approaches. Phylogenetic analysis of survey sequences has shown P. penetrans to be closely related to Bacillus and to have a diverse range of collagen-like fibres which we hypothesise to be involved in the endospore adhesion. However, due to the obligately hyperparasitic nature of Pasteuria species, identifying and characterizing these collagenous-like proteins through gain of function has proved difficult and new approaches are required.
Methods and Results: Using antibodies raised to synthetic peptides based onPasteuria collagen-like genes we show similarities between P. penetrans and the more easily cultured bacterium Bacillus thuringiensis and suggest it be used as a gain of function platform/model. Using immunological approaches similar proteins between P. penetrans and B. thuringiensis are identified and characterized, one >250 kDa and another ~72 kDa are glycosylated with N-acetylglucosamine and both of which are digested if treated with collagenase. These treatments also affected endospore attachment and suggest these proteins are involved in adhesion of endospores to nematode cuticle.
Conclusion:There are conserved similarities in the collagen-like proteins present on the surface of endospores of both P. penetrans and B. thuringiensis.
Significance and Impact of Study:As B. thuringiensis is relatively easy to culture and can be transformed, it could be developed as a platform for studying the role of the collagen-like adhesins from Pasteuria in endospore adhesion.
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