Chapter 46 - MetschnikowiaKamienski (1899)

Abstract

This chapter studies the genus Metschnikowia. In the determination of the asexual reproduction, it is seen that budding is multilateral. Cells are spherical to ellipsoid or can be pyriform, cylindroid, or lunate. Pseudohyphae are poorly developed but rarely lacking. Some species form long aseptate germ tubes reminiscent of true hyphae. In sexual reproduction it is found that the asci are elongate, clavate, sphaeropedunculate, or ellipsoidopedunculate. Ascospores are needle-shaped, attenuated at one or both ends, occasionally swollen along one half, and without a whip-like appendage. One or two spores form per ascus, depending on the species. The chapter also discusses physiology/biochemistry and phylogenetic placement of the genus. The type species taken is Metschnikowia bicuspidata. The extent of sequence divergence in Metschnikowia is worthy of attention. Measured in terms of substitutions in ribosomal genes, the phylogenetic distance between members of the various subclades can exceed the distance separating Schizosaccharomyces and various genera in the Saccharomycetaceae. Adherence to a typological genus definition, based on the molecular clock, would dictate the subdivision of Metschnikowia into several genera that would be distinguishable only on the basis of the sequences. The principal habitats where Metschnikowia species are encountered with regularity include the flowers, fruit, other plant tissues, and the digestive tract or frass of some of the insects that visit these substrates. The nature of the association between Metschnikowia species and insects remains unclear, but it is clear that the relationship can be highly specific.