Abstract
Trichinellosis caused by parasitic nematodes of the genus Trichinella may result in human morbidity and mortality worldwide. Deciphering processes that drive species diversity and adaptation are key to understanding parasitism and developing effective control strategies. Our goal was to identify genes that are under positive selection and possible mechanisms of adaptive evolution of Trichinella spiralis genes using a comparative genomic analysis with the genomes of Brugia malayi, Trichuris suis, Ancylostoma ceylanicum, and Caenorhabditis elegans. The CODEML program derived from the PAML package was used to deduce the most probable dN/dS ratio, a measurement to detect genes/proteins undergoing adaptation. For each pair of sequences, those with a dN/dS ratio > 1 were considered positively selected genes (PSGs). Altogether, 986 genes were positively selected (p-value < 0.01). Genes involved in metabolic pathways, signaling pathways, and cytosolic DNA-sensing pathways were significantly enriched among the PSGs. Several PSGs are associated with exploitation of the host: modification of the host's metabolism, creation of new parasite-specific morphological structures between T. spiralis and the host interface, xenobiotic metabolism to combat low oxygen concentrations and host toxicity, muscle cell transformation, cell cycle arrest, DNA repair processes during nurse cell formation, antiapoptotic factors, immunomodulation, and regulation of epigenetic processes. Some of the T. spiralis PSGs have C. elegans orthologs that confer severe or lethal RNAi phenotypes. Fifty-seven PSGs in T. spiralis were analyzed to encode differentially expressed proteins. The present study utilized an overall comparative genomic analysis to discover PSGs within T. spiralis and their relationships with biological function and organism fitness. This analysis adds to our understanding of the possible mechanism that contributes to T. spiralis parasitism and biological adaptation within the host, and thus these identified genes may be potential targets for drug and vaccine development.