Abstract
The phylum Apicomplexa is a quintessentially parasitic lineage, whose members infect a broad range of animals. One exception to this may be the apicomplexan genus Nephromyces, which has been described as having a mutualistic relationship with its host. Here we analyze transcriptome data from Nephromyces and its parasitic sister taxon, Cardiosporidium, revealing an ancestral purine degradation pathway thought to have been lost early in apicomplexan evolution. The predicted localization of many of the purine degradation enzymes to peroxisomes, and the in silico identification of a full set of peroxisome proteins, indicates that loss of both features in other apicomplexans occurred multiple times. The degradation of purines is thought to play a key role in the unusual relationship between Nephromyces and its host. Transcriptome data confirm previous biochemical results of a functional pathway for the utilization of uric acid as a primary nitrogen source for this unusual apicomplexan.
Highlights
Apicomplexans are most well known for being parasites of humans and livestock
Despite the extensive search for peroxisome-associated functions in apicomplexans, no genes involved in purine degradation were found in other sequenced apicomplexan genomes, with the lone exception of allantoicase in Plasmodium (Gardner et al 2002)
In addition to highly expressed transcripts for the genes involved, all of the identified purine degradation genes and Malate synthase (MLS) have been located on genomic contigs from Nephromyces
Summary
Apicomplexans are most well known for being parasites of humans and livestock. Species in the genus Plasmodium, for instance, are the etiological agents of malaria. Apicomplexan species show tremendous variation in transmission methods, life cycles, host range, host manipulation strategies, cell-types infected, metabolic capabilities, immune evasion strategies, and virulence (Roos 2005; Reid et al 2012; Kemp et al 2013; Cardoso et al 2016). Because of this variability, there are few apicomplexan characteristics shared throughout the phylum. Nephromyces was misclassified as a fungus for more than a 100 years, based on long hyphal-like cell structures, flagellated spores interpreted by some as chytrid zoospores and cell walls made of a chitin (Giard 1888) It was not until the application of molecular methods that Nephromyces was confirmed as a member of the derived apicomplexans (Saffo et al 2010). These include amino acid metabolism and vitamin metabolism (Moran et al 2005), nitrogen metabolism (LopezSanchez et al 2009), defense (De Souza et al 2009), chemotrophic energy production (Urakawa et al 2005), and photosynthesis (Marin et al 2005), to name a few
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