Biology, ecology and ultrastructure of Ascobotryozyma and Botryozyma, unique commensal nematode-associated yeasts.

Ascobotryozyma (anamorph Botryozyma) is an ascomycetous yeast genus characterized by its unusual morphology and ability to attach to free-living nematodes in the genus Panagrellus. Other than species descriptions for four taxa little is known about these yeasts. Investigations were carried out to determine the ecological relationship and specificity with nematodes in addition to examining basic cell structure, thallus development and sexual reproduction. Based on previous examinations of the yeast and nematode it was hypothesized the fungus did not parasitize the nematode but instead remained attached to nematodes for dispersal. Electron micrographs supported our hypotheses and revealed a specialized cell wall and mucilage that aid in attachment to the nematode cuticle. Tests to determine the ability of Ascobotryozyma and Botryozyma to attach to different nematode taxa revealed that attachment varies across taxonomic groups. Examinations of thallus cells, thallus growth, cell fusion and ascosporogenesis are presented. This study provides insight into an otherwise cryptic yeast genus.