title: A new oomycete species parasitic in nematodes, Chlamydomyzium dictyuchoides sp. nov.: developmental biology and phylogenetic studies.
abstract: The genus Chlamydomyzium is a little studied holocarpic oomycete parasite of nematodes of uncertain phylogenetic and taxonomic position. A new holocarpic species, Chlamydomyzium dictyuchoides, is described which has usually refractile cytoplasm and a dictyuchoid pattern of spore release. This new species infects bacteriotrophic rhabditid nematodes and was isolated from diverse geographical locations. Infection was initiated by zoospore encystment on the host surface and direct penetration of the cuticle. A sparsely branched, constricted, refractile thallus was formed which eventually occupied almost the entire host body cavity, often accompanied by complete dissolution of the host cuticle. Walled primary cysts formed throughout the thallus and each cyst released a single zoospore via an individual exit papillum, leaving a characteristic dictyuchoid wall net behind. At later stages of infection some thalli formed thick-walled stellate resting spores in uniseriate rows. Resting spore formation appeared to be parthenogenetic and was not accompanied by the formation of antheridial compartments. These spores had ooplast-like vacuoles and thick multi-layered walls, both of which suggest they were oospores. The maximum likelihood tree of sequences of the small ribosomal subunit (SSU) gene placed this new isolate in a clade before the main saprolegnialean and peronosporalean lines diverge. A second undescribed Chlamydomyzium sp., which has direct spore release forms a paraphyletic clade, close to C. dictyuchoides and Sapromyces. The fine structure of other documented Chlamydomyzium species was compared, including an undescribed (but sequenced) isolate, SL02, from Japan, Chlamydomyzium anomalum and Chlamydomyzium oviparasiticum. Chlamydomyzium as currently constituted is a paraphyletic genus that is part of a group of phylogenetically problematic early diverging clades that lie close to both the Leptomitales and Rhipidiales.
authors.affiliation: School of Biology, Newcastle University, Newcastle upon Tyne NE1 7RU, UK. Electronic address: gordon.beakes@ncl.ac.uk.
authors.forename: Gordon W
authors.initials: GW
authors.lastname: Beakes
authors.affiliation: Department of Biological Sciences, Northern Illinois University, Dekalb, IL 60115, USA; Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton, East Sussex BN1 9RQ, UK. Electronic address: sally@glockling.com.
authors.forename: Sally L
authors.initials: SL
authors.lastname: Glockling
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Michigan, Kraus Natural Science Bld., Rm. 1008, 830 North University, Ann Arbor, MI 48109, USA. Electronic address: tyjames@umich.edu.
authors.forename: Timothy Y
authors.initials: TY
authors.lastname: James
mesh_terms: D000825:Animal Structures / Q000382:microbiology*; D000818:Animals; D016000:Cluster Analysis; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D007564:Japan; D009348:Nematoda / Q000469:parasitology*; D009868:Oomycetes / Q000145:classification* / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D010802:Phylogeny; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D004275:DNA, Ribosomal; D012337:RNA, Ribosomal, 18S
keywords: Leptomitales; Rhipidiales; SSU rDNA tree; Ultrastructure; Zoosporogenesis