Taxonomic Revision of the pulcherrima Clade of Metschnikowia (Fungi): Merger of Species

Matthias Sipiczki

doi:10.3390/taxonomy2010009

Abstract

The type strains of 10 small-spored species of the ascomycetous yeast genus Metschnikowia usually form a compact group on the phylogenetic trees inferred from barcode sequences. Based on the name of the species, which was described first (Metschnikowia pulcherrima), the group is frequently referred to as the pulcherrima clade. All strains produce the iron-chelate pigment pulcherrimin and have antagonistic effects on many microorganisms. Recent results of molecular phylogenetic, genetic, and genomic research raised doubts about the taxonomic division of the clade. Those data—combined with results obtained in this study by comprehensive analysis of primary and secondary barcode sequences, physiological tests, and hybridisation experiments—demonstrate that the species cannot be distinguished from each other by the criteria of any of the phenotypic, phylogenetic, and biological species concepts. Therefore, I propose that the species of the pulcherrima clade be merged into one species under the oldest species name, M. pulcherrima.

Highlights

Metschnikowia (Saccharomycetales) is a large genus of budding yeasts currently comprising 71 species and a large number of related strains (Mycobank and NCBI Taxonomy Database, 31 October 2020)
As pulcherriminic acid can be secreted into the environment, pigmented halos can frequently be seen around the pigmented colonies
Numerous pulcherrima-clade strains have been found to have antagonistic activity against bacteria and fungi (e.g., [2–7]). The strength of their antagonistic effect correlates with the intensity of the extracellular production of pulcherrimin, and supplementation of the medium with ferric salts reduces the size of both the pigmented halo and the inhibition zone around the Metschnikowia colony

Summary

Introduction

Metschnikowia (Saccharomycetales) is a large genus of budding yeasts currently comprising 71 species and a large number of related strains (Mycobank and NCBI Taxonomy Database, 31 October 2020). Numerous pulcherrima-clade strains have been found to have antagonistic activity against bacteria and fungi (e.g., [2–7]) The strength of their antagonistic effect correlates with the intensity of the extracellular production of pulcherrimin, and supplementation of the medium with ferric salts reduces the size of both the pigmented halo and the inhibition zone around the Metschnikowia colony. From these results, it was inferred that the pulcherrimin-producing strains antagonise fungal and bacterial growth by iron depletion [2]. Due to their antimicrobial activities, these strains can be used as biological agents to protect agricultural commodities and food products against pathogenic and destructive microorganisms (for a review, see [10])

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Results

Conclusion