Whole Genome Sequencing And Comparative Genomic Analysis Of Three Zoonotic Gastrointestinal Parasites

The foodborne and waterborne pathogens,Cyclospora spp.and Cryptosporidium spp.,are diarrhea-causing pathogens in humans and animals.They threaten human health and cause economy loss as well.Both Cyclospora and Cryptosproidium belong to Apicomplexa phylum and consist of multiple species,with most species possess host specificity or tissue tropism.So far,there are complete genomes of three Cryptosporidium spp.and no genome of Cyclospora spp.available,which hampers the study of the pathogen biology,molecular mechanism of host cell invasion,and the determinants of tissue tropism and host specificity of these pathogens.In this study,we sequenced the whole genome of Cyclospora cayetanensis infecting humans,Cryptosporidium ubiquitum with broad host specificity and the gastric Cryptosporidium andersoni.Comparative genomic analysis was conducted on genome organization,metabolic pathways and the potential invasion mechanism of these pathogens.The main conclusion were as following.(1)The draft genomes of C.cayetanensis,C.ubiquitum and C.andersoni were obtained after assembling the raw sequencing reads.The genome sizes of Cyclospora and Cryptosporidium are about 45 M and 9 M,respectively.(2)Comparative genomic analysis revealed that C.cayetanensis has the similar genome organization and metabolic pathways with Eimeria tenella,but the mitochondrial-derived amino acid metabolism and post-translational glycosylation are different from the latter.(3)The genome features,sequence identity,and syntenic relationship between intestinal C.ubiquitum and C.parvum are very similar to each other,but they are different from the gastric C.andersoni in genome sequence identity and syntenic organization.Comparing with C.parvum and C.hominis,C.andersoni possesses more aerobic metabolism and a nearly complete electron transport chain,whereas C.ubiquitum has further reduction in the electron transport system and polyisprenoid and ubiquinone biosynthesis,indicating that the reductive evolution among apicomplexans happened in the differentiation of Cryptosporidium spp.(4)The comparison of host cell invasion-related proteins revealed that C. cayetanensis has an invasion process similar to that of T.gondii,but possesses divergent surface antigens.The significant reduction in the number of secreted protein phosphatases,protein kinases and other signal pathway related protein factors in C.cayetanensis compared toT.gondii indicated that the former has the limited capabilities in regulating host cell cytosol and nuclear activities or uses a different system.On the other hand,mucin-like glycoproteins associated with host cell adhesion and invasion are highly divergent between thegastric C.andersoni and intestinal Cryptosporidium spp.,suggesting the likely involvement of this protein family in tissue tropism of Cryptosporidium spp.In addition the observation of the apparentdifference in the number of genes of secreted insulinases and MEDLE proteins among all Cryptosporidium spp.suggested that they may be related to the host specificity of Cryptosporidium spp.The findings in this study improve our understanding of the biology and evolution of these pathogenic microorganisms and facilitate the development of advanced diagnostic tools and therapeutic agents.