Abstract
Yeasts affiliated with the Metschnikowia pulcherrima clade (subclade) of the large ascomycetous genus Metschnikowia frequently turn out to produce the characteristic maroon-red pulcherrimin when tested for pigment production and prove to exert antagonistic effects on many types of microorganisms. The determination of the exact taxonomic position of the strains is hampered by the shortage of distinctive morphological and physiological properties of the species of the clade and the lack of rDNA barcode gaps. The rDNA repeats of the type strains of the species are not homogenized and are assumed to evolve by a birth-and-death mechanism combined with reticulation. The taxonomic division is further hampered by the incomplete biological (reproductive) isolation of the species: certain type strains can be hybridized and genome sequencing revealed chimeric genome structures in certain strains that might have evolved from interspecies hybrids (alloploid genome duplication). Various mechanisms have been proposed for the antimicrobial antagonism. One is related to pulcherrimin production. The diffusible precursor of pulcherrimin, the pulcherriminic acid is secreted by the cells into the environment where it forms the insoluble pulcherrimin with the ferric ions. The lack of free iron caused by the immobilization of ferric ions inhibits the growth of many microorganisms. Recent results of research into the complexity of the taxonomic division of the pulcherrimin-producing Metschnikowia yeasts and the mechanism(s) underlying their antimicrobial antagonism are discussed in this review.
Highlights
Metschnikowia Kamienski (1899) is a large ascomycetous genus currently comprising 79 species (Mycobank, 04. 2020) but the number or species is continuously growing
Cloning of individual DNA molecules from amplified D1/D2 and ITS sequences revealed that the type strains of the species M. andauensis and M. fructicola have diverse rDNA repeats in their genomes [13,14]
Correlation and causative relationship between iron depletion and antagonism was later observed in many other pulcherrimin-producing Metschnikowia strains, including the type strains of the species (e.g., [7,8,10,11,21,71,72,73])
Summary
Metschnikowia Kamienski (1899) is a large ascomycetous genus currently comprising 79 species (Mycobank, 04. 2020) but the number or species is continuously growing. The M. pulcherrima clade of the genus contains seven validly described species that share the ability to produce pulcherrimin, a maroon-red pigment (reviewed in [1,2]). These species and the strains closely related to them have broad biotechnological potential for application in various industrial processes. Due to the large fatty globules in their chlamydospores (“pulcherrima cells”), the strains are outstanding candidates for low-cost lipid production (reviewed in [4]) Their most intensively studied property is the strong antimicrobial activity (Figure 1A–C) (e.g., [5,6,7,8,9,10,11,12]).
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