The microneme proteins CTRP and SOAP are not essential for Plasmodium berghei ookinete to oocyst transformation in vitro in a cell free system

Background: Two Plasmodium berghei ookinete micronemal proteins, circumsporozoite and TRAP related protein (CTRP) and secreted ookinete adhesive protein (SOAP) both interact with the basal lamina component laminin. Following gene disruption studies it has been proposed that, apart from their role in motility, these proteins may be required for interactions leading to ookinete-to-oocyst transformation. Methods: CTRP and SOAP null mutant P. berghei ookinetes were compared to P. berghei ANKA wild-type for their ability to transform and grow in vitro. To confirm in vitro findings for P. berghei CTRP-KO ookinetes were injected into the haemocoel of Anopheles gambiae female mosquitoes. Results: Transformation, growth, and viability were comparable for the gene disrupted and wildtype parasites. P. berghei CTRP-KO ookinetes were able to transform into oocysts in the haemocoel of An. gambiae mosquitoes. Conclusion: Neither CTRP nor SOAP is required for parasite transformation in vitro. By-passing the midgut lumen allows for the transformation of P. berghei CTRP-KO ookinetes suggesting that it is not required for transformation in vivo.