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Features of iron accumulation at high concentration in pulcherrimin-producing Metschnikowia yeast biomass
Kęstutis Mažeika1, Laurynas Šiliauskas2, Gražina Skridlaitė2
1Center for Physical Sciences and Technology, Savanorių 231, 02300, Vilnius, Lithuania. kestutis.mazeika@ftmc.lt.
Abstract:
In previous studies it was found that the antimicrobial properties of pulcherrimin-producing Metschnikowia species are related to the formation of a red pigment-pulcherrimin and sequestration of free iron from their growth medium. For strains of Metschnikowia pulcherrima, M. sinensis, M. shaxiensis, and M. fructicola, at a high, ≈80 mg/kg, elemental Fe concentration in agar growth media we observed the essentially different (metal luster, non-glossy rust like, and colored) yeast biomass coatings. For the studied strains the optical and scanning electron microscopies showed the increased formation of chlamydospores that accumulate a red pigment-insoluble pulcherrimin rich in iron. The chlamydospore formation and decay depended on the iron concentration. In this study pulcherrimin in biomass of the selected Metschnikowia strains was detected by Mössbauer spectroscopy. At ≈80 mg/kg elemental Fe concentration the Mössbauer spectra of biomass of the studied strains were almost identical to these of purified pulcherrimin. Iron in pulcherrimin reached ≈1% of biomass by weight which is very high in comparison with elemental Fe percentage in growth medium and is not necessary for yeast growth. The pulcherrimin in biomass was also observed by Mössbauer spectroscopy at lower, ≈5 mg/kg, elemental Fe concentration. Through chemical binding of iron pulcherrimin sequestrates the soluble Fe in the growth media. However, at high Fe concentrations, the chemical and biochemical processes lead to the pulcherrimin accumulation in biomass chlamydospores. When soluble iron is sequestrated or removed from the growth media in this way, it becomes inaccessible for other microorganisms.
Insights
Metschnikowia yeast produces pulcherrimin, a red pigment that sequesters iron. This pigment accumulates in chlamydospores, impacting yeast biomass appearance and potentially inhibiting other microbes by limiting iron availability.
Area of Science:
- Microbiology
- Biochemistry
- Biophysics
Background:
- Pulcherrimin-producing Metschnikowia species exhibit antimicrobial properties linked to pulcherrimin pigment formation and iron sequestration.
- Previous studies suggest a correlation between pulcherrimin production and iron availability in the growth medium.
Purpose of the Study:
- To investigate the role of iron concentration on pulcherrimin formation and accumulation in Metschnikowia yeast biomass.
- To characterize the iron-containing pulcherrimin pigment within yeast chlamydospores using Mössbauer spectroscopy.
Main Methods:
- Cultivation of selected Metschnikowia strains (M. pulcherrima, M. sinensis, M. shaxiensis, M. fructicola) on agar media with varying elemental iron concentrations (≈80 mg/kg and ≈5 mg/kg).
- Optical and scanning electron microscopy to observe yeast biomass morphology and chlamydospore formation.
- Mössbauer spectroscopy to detect and analyze pulcherrimin in yeast biomass and compare it with purified pulcherrimin.
Main Results:
- Distinct yeast biomass coatings were observed at high iron concentrations (≈80 mg/kg), differing in appearance (metal luster, non-glossy rust-like, colored).
- Increased formation of iron-rich, pulcherrimin-accumulating chlamydospores was observed, with formation and decay dependent on iron concentration.
- Mössbauer spectroscopy confirmed the presence of pulcherrimin in biomass at both high (≈80 mg/kg) and lower (≈5 mg/kg) iron concentrations, with spectra matching purified pulcherrimin at high iron levels.
- Iron content in pulcherrimin reached approximately 1% of biomass by weight, significantly exceeding the iron percentage in the growth medium.
Conclusions:
- Pulcherrimin formation and accumulation in Metschnikowia chlamydospores are significantly influenced by iron availability in the growth medium.
- Mössbauer spectroscopy is a suitable method for detecting pulcherrimin in yeast biomass.
- Iron sequestration by pulcherrimin, particularly at high concentrations leading to chlamydospore accumulation, renders iron inaccessible to other microorganisms, contributing to the antimicrobial properties of these yeasts.
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