Abstract
Members of Myxozoa, a parasitic metazoan taxon, have considerable detrimental effects on fish hosts and also have been associated with human food-borne illness. Little is known about their biology and metabolism. Analysis of the genome of Thelohanellus kitauei and comparative analysis with genomes of its two free-living cnidarian relatives revealed that T. kitauei has adapted to parasitism, as indicated by the streamlined metabolic repertoire and the tendency toward anabolism rather than catabolism. Thelohanellus kitauei mainly secretes proteases and protease inhibitors for nutrient digestion (parasite invasion), and depends on endocytosis (mainly low-density lipoprotein receptors-mediated type) and secondary carriers for nutrient absorption. Absence of both classic and complementary anaerobic pathways and gluconeogenesis, the lack of de novo synthesis and reduced activity in hydrolysis of fatty acids, amino acids, and nucleotides indicated that T. kitauei in this vertebrate host–parasite system has adapted to inhabit a physiological environment extremely rich in both oxygen and nutrients (especially glucose), which is consistent with its preferred parasitic site, that is, the host gut submucosa. Taking advantage of the genomic and transcriptomic information, 23 potential nutrition-related T. kitauei-specific chemotherapeutic targets were identified. This first genome sequence of a myxozoan will facilitate development of potential therapeutics for efficient control of myxozoan parasites and ultimately prevent myxozoan-induced fish-borne illnesses in humans.
Highlights
The international market for fish and fish products has grown remarkably, and global fish consumption was estimated to be 140.5 million tons in 2013
Aided by transcriptome sequencing of the myxospore stage, we identified a range of potential T. kitauei chemotherapeutic targets, which may facilitate the development of novel therapeutic agents against myxozoan parasites and relieve the potential threat of myxozoan zoonoses to human consumers
The phylogenetic analysis showed that the parasite from common carp in this study is clustered with T. kitauei-China (HQ115585) and T. kitauei-Korea (HM624024) with 100% bootstrap confidence values
Summary
The international market for fish and fish products has grown remarkably, and global fish consumption was estimated to be 140.5 million tons in 2013 (http://www.thefishsite. com/reports/?id=2253&country=WW). Along with the rapid growth in fish consumption, incidence of fish-borne parasitic zoonoses increased (Dos Santos and Howgate 2011). Most myxozoans are not highly pathogenic for fish hosts, some cause disease and impact upon wild and farmed fish populations (Gomez et al 2014). The impact of myxozoans has further exacerbated, as indicated by the observed increase in fish-to-fish transmission rate as well ß The Author(s) 2014.
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