Metschnikowia: half tetrads, a regicide and the fountain of youth.

The purpose of this review is to introduce Metschnikowia to the yeast researcher community and to convince readers that the genus is a worthwhile object of study in developmental biology, genetics, ecology and biotechnology. Metschnikowia sits at the foundation of modern immunology, having been instrumental in the discovery of animal phagocytosis. Some 81 species form a monophyletic group within the Metschnikowiaceae, which also include the smaller genus Clavispora and a few clades of Candida species. The family stands out by the habit of forming, by meiosis, only two ascospores, which in Metschnikowia are needle shaped. In some cases, the spores can reach enormous proportions, exceeding 200 µm in length; in others, ascus formation is preceded by the development of chlamydospores. The adaptive value of such features remains to be elucidated. Extensive genetic studies are lacking, but attempts to apply methods developed for model species have been successful. Some species are found at the plant-insect interface whereas others are pathogens of aquatic animals and have served as model organisms in the exploration of host-parasite theory. Some species are globally distributed and others exhibit extreme endemism. Many species are remarkably easy to recover by sampling their known habitats. M. pulcherrima and close relatives may play an important role in wine quality and produce pulcherrimin, an iron-dipeptide complex that can interfere with the growth of other microorganisms. Some symbiotic species incapable of growth in culture media have been assigned to the genus, but their kinship with the group remains to be demonstrated.