title: Nephromyces, a beneficial apicomplexan symbiont in marine animals.
abstract: With malaria parasites (Plasmodium spp.), Toxoplasma, and many other species of medical and veterinary importance its iconic representatives, the protistan phylum Apicomplexa has long been defined as a group composed entirely of parasites and pathogens. We present here a report of a beneficial apicomplexan: the mutualistic marine endosymbiont Nephromyces. For more than a century, the peculiar structural and developmental features of Nephromyces, and its unusual habitat, have thwarted characterization of the phylogenetic affinities of this eukaryotic microbe. Using short-subunit ribosomal DNA (SSU rDNA) sequences as key evidence, with sequence identity confirmed by fluorescence in situ hybridization (FISH), we show that Nephromyces, originally classified as a chytrid fungus, is actually an apicomplexan. Inferences from rDNA data are further supported by the several apicomplexan-like structural features in Nephromyces, including especially the strong resemblance of Nephromyces infective stages to apicomplexan sporozoites. The striking emergence of the mutualistic Nephromyces from a quintessentially parasitic clade accentuates the promise of this organism, and the three-partner symbiosis of which it is a part, as a model for probing the factors underlying the evolution of mutualism, pathogenicity, and infectious disease.
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138-2902, USA. mbsaffo@post.harvard.edu
authors.forename: Mary Beth
authors.initials: MB
authors.lastname: Saffo
authors.forename: Adam M
authors.initials: AM
authors.lastname: McCoy
authors.forename: Christopher
authors.initials: C
authors.lastname: Rieken
authors.forename: Claudio H
authors.initials: CH
authors.lastname: Slamovits
mesh_terms: D000818:Animals; D016782:Apicomplexa / Q000502:physiology* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D010802:Phylogeny; D013559:Symbiosis; D014122:Toxoplasma / Q000502:physiology; D014561:Urochordata / Q000502:physiology* / Q000648:ultrastructure