Biological Activity of Pulcherrimin from the Meschnikowia pulcherrima Clade

Abstract

Pulcherrimin is a secondary metabolite of yeasts belonging to the Metschnikowia pulcherrima clade, and pulcherrimin formation is responsible for the antimicrobial action of its producers. Understanding the environmental function of this metabolite can provide insight into various microbial interactions and enables the efficient development of new effective bioproducts and methods. In this study, we evaluated the antimicrobial and antiadhesive action of yeast pulcherrimin, as well as its protective properties under selected stressful conditions. Classical microbiological plate methods, microscopy, and physico-chemical testing were used. The results show that pure pulcherrimin does not have antimicrobial properties, but its unique hydrophilic nature may hinder the adhesion of hydrophilic bacterial cells to abiotic surfaces. Pulcherrimin also proved to be a good cell protectant against UV-C radiation at both high and low temperatures.

Keywords: Metschnikowia; UV–C light; antibiofilm; protection; pulcherrimin; temperature; water affinity.

Figure 1

Comparison of antimicrobial activity of Metschnikowia sp. LOCK1144 cells and pure pulcherrimin suspension (~3% w/v) against tested microorganisms. Samples with pure pulcherrimine were taken as controls. Values show the mean ± standard deviation (SD, n = 3). Values with different letters are statistically different: ^a: p ≥ 0.05; ^c: p < 0.005.

Figure 2

Surface free energy of glass and glass with yeast pulcherrimin evaluated for two solvents: a dispersive solvent (glycerol), and a polar solvent (water). Glass surface and its SFE components were taken as references. Values show the mean ± standard deviation (SD, n = 3). Values with different letters are statistically different: ^b: 0.005 < p < 0.05; ^c: p < 0.005.

Figure 3

Adhesion coefficient A evaluated for microbial cultures incubated in culture media with and without pulcherrimin supplementation. Values show the mean ± standard deviation (SD, n = 3). Results obtained in minimal medium with pulcherrimin were compared with those for minimal medium without supplementation (control). Values with different letters are statistically different: ^a: p ≥ 0.05; ^b: 0.005 < p < 0.05.

Figure 4

Attachment of microbial cells to glass surface. Yeast cells of W. anomalus cultivated without pulcherrimin (a) and with pulcherrimin (b). Bacterial cells of A. lannensis FMW2 cultivated without pulcherrimin (c) and with pulcherrimin (d). Bars represent 20 μm.

Figure 5

Decimal reduction times determined for three strains of M. pulcherrima clade: M. pulcherrima CCY 29-2-145, Metschnikowia sp. LOCK1135, and Metschnikowia sp. LOCK1144. Values show the mean ± standard deviation (SD, n = 3). Results obtained for minimal medium (control samples) were compared with those for minimal medium with Fe(III) ions (pulcherrimin production). Values with different letters are statistically different: ^c: p < 0.005.

Figure 6

Comparison of the number of viable yeast cells after 6 months of storage at −196 °C in the presence of different cryoprotectants: DMSO (control) and DMSO with pulcherrimin (a); DMSO with glycoprotein (control) and DMSO with pulcherrimin (b). Yeast strains: 1—C. macerans CCY 10-1-17; 2—G. candidum CCY 16-1-25; 3—P. flavescens CCY 17-3-34; 4—S. metaroseus CCY 19-6-22; 5—R. dairenensis CCY 20-2-25; 6—F. capsuligenum CCY 29-143-1; 7—C. zemplinina CCY 20-178-1; 8—A. porosum CCY 30-18-5; 9—S. pombe CCY 44-1-3. Values with different letters are statistically different: ^a: p ≥ 0.05; ^b: 0.005 < p < 0.05; ^c: p < 0.005.

Figure 7

Morphology and division of S. pombe cells during cultivation in a culture medium: without pulcherrimin (a), with pulcherrimin (b). S. pombe cells show abnormal multiple divisions in the presence of pulcherrimin (white circles).