Biological control against microbial infections has great potential as an alternative approach instead of fungicidal chemicals, which can cause environmental pollution. The pigment producer Metschnikowia andauensis belongs to the antagonistic yeasts, but details of the mechanism by which it inhibits the growth of other microbes are less known. Our results confirmed its antagonistic capacity on other yeast species isolated from fruits or flowers and demonstrated that the antagonistic capacity was well correlated with the size of the red-pigmented zone. We have isolated and characterized its red pigment, which proved to be the iron-chelating pulcherrimin. Its production was possible even in the presence of 0.05 mg/ml copper sulfate, which is widely used in organic vineyards because of its antimicrobial properties. Production and localization of the pulcherrimin strongly depended on the composition of the media and other culture factors. Glucose, galactose, disaccharides, and the presence of pectin or certain amino acids clearly promoted pigment production. Higher temperatures and iron concentration decreased the diameter of red-pigmented zones.
Fig: M. andauensis is able to inhibit growth of yeasts and produces pulcherrimin. The inhibitory zone of M. andauensis on a Candida magnifica (11–1366) lawn—indicated with black *—correlated with the red ring formed around the M. andauensis cells—indicated with black arrow (A). Similar results were obtained on lawns prepared from several other species). The UV–Vis spectrum of the red pigment revealed absorption maxima at 380 and 480 (B). The localisation and colour intensity of the red pigment can depend on the composition (C, D) and iron content of the medium (E). (C) YPA, (D) PDA + 0.001 mg/ml FeCl3, (E) EMMA, EMMA supplemented with 0.05 and 1 mg/ml FeCl3 (from left to right). Growth inhibition of Starmerella caucasica (11–1071) by cyclo-leucyl-leucyl (F). The cyclo-leucyl-leucyl solution was diluted with DMSO (F1) or PEG 4000 (F2). Black arrows show the inhibited zone, where the cells were not able to grow compared to the other regions of the agar plates (similar results were obtained in the case of Candida stigmatis (11–465) and Saccharomyces cerevisiae lawn (10–642). Concentrations of the cyclo-leucyl-leucyl were 100, 50 or 33 mg/ml. PEG and DMSO indicate that PEG 4000 and DMSO were dropped without cyclo-leucyl-leucyl.
The effect of pH on pigment production varied depending on whether it was tested in liquid or solid media. In addition, our results suggest that other mechanisms besides the iron depletion of the culture media may contribute to the antagonistic capacity of M. andauensis.
Horváth, E., Dályai, L., Szabó, E. et al. The antagonistic Metschnikowia andauensis produces extracellular enzymes and pulcherrimin, whose production can be promoted by the culture factors. Sci Rep 11, 10593 (2021). https://doi.org/10.1038/s41598-021-89982-y