Zoospore ultrastructure and phylogenetic position of Phlyctochytrium aureliae Ajello is revealed (Chytridiaceae, Chytridiales, Chytridiomycota)

From forest soils in Scotland Phlyctochytrium aureliae was observed and brought into pure culture. Previously included in a molecular phylogenetic study of Chytridiales as Phlyctochytrium sp. KP 061, the organism groups with Phlyclochytrium planicorne, P. bultatum, Chytridium olla and C. lagenaria in the family Chytridiaceae. Thallus morphology and development as well as zoospore ultrastructure are detailed herein. The sporangium is epibiotic, spherical or subspherical, apophysate or non-apophysate, and ornamented with dentate enations. The overall zoospore ultrastructural features are consistent with the Group II type zoospore that characterizes family Chytridiaceae in the Chytridiales, although the zoospore also has two character states unique to this taxon: the MLC cisterna fenestrations are one-third to one-half the diameter of fenestrations in other Chytridiaceae zoospores and an accumulation of electron-dense material (a kinetosome-associated structure, or KAS) proximal to the kinetosome and non-flagellated centriole is extensive and unique. This study verifies that zoospore ultrastructure of P. aureliae zoospores places this species in the Chytridiales and Chytridiaceae, as indicated in a previous molecular phylogenetic study.