Pulcherrimin Production by Endophytic <i>Metschnikowia pulcherrima</i> : Fermentation Performance and Antimicrobial Activity

Abstract Endophytic yeasts of the Metschnikowia pulcherrima clade are recognized as natural producers of pulcherrimin, an iron-chelating red pigment associated with antimicrobial activity. However, endophytic isolates from arid Central Asian fruit trees remain unexplored, and their pulcherrimin biosynthetic capacity is poorly characterized. In this study, five endophytic M. pulcherrima strains were isolated from apricot, persimmon, peach and pomegranate fruits in Uzbekistan and identified using MALDI-TOF MS and ITS sequencing. The strains were cultivated in FeCl₃-supplemented Sabouraud medium, and pulcherrimin was extracted and quantified using a gravimetric workflow with biological triplicates. Pigment yields ranged from 420.6 to 776.4 mg/L, representing some of the highest values reported for non-engineered isolates under flask conditions. Antimicrobial activity was evaluated by agar well diffusion assays against Staphylococcus aureus , Bacillus subtilis , Escherichia coli , Pseudomonas aeruginosa and Candida albicans , with inhibition zones reaching 18–23 mm depending on the strain. Nano-LC-MS/MS analysis confirmed the presence of key intermediates of the pulcherrimin biosynthetic pathway, including cyclo(Leu–Leu) and pulcherriminic acid, supporting the metabolic origin of the pigment. These findings reveal that endophytic M. pulcherrima from Uzbekistan fruit trees and shrubs constitute highly productive natural sources of pulcherrimin and represent promising candidates for future fermentation optimization and development of natural antimicrobial pigments. Paragraph on importance This study provides the first systematic evidence that endophytic Metschnikowia pulcherrima yeasts isolated from fruit trees in Central Asia possess an exceptional capacity to produce pulcherrimin, a natural antimicrobial pigment. Strains obtained under the environmental conditions of Uzbekistan produced remarkably high levels of pulcherrimin (up to 776 mg/L) under simple, non-genetically modified fermentation conditions, exceeding yields previously reported for yeast and bacterial sources. The iron-chelating mechanism characteristic of pulcherrimin confers broad-spectrum antimicrobial activity against bacteria and yeasts. These findings highlight endophytic yeasts as environmentally safe and sustainable sources of natural antimicrobial pigments and identify Central Asia as a previously unexplored reservoir of high-value microbial resources with significant biotechnological potential.

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