Features of iron accumulation at high concentration in pulcherrimin-producing Metschnikowia yeast biomass

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, approximate to 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 Mossbauer spectroscopy. At approximate to 80 mg/kg elemental Fe concentration the Mossbauer spectra of biomass of the studied strains were almost identical to these of purified pulcherrimin. Iron in pulcherrimin reached approximate to 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 Mossbauer spectroscopy at lower, approximate to 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. [GRAPHICS] .

Automated summary

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. Different strains of Metschnikowia exhibit distinct yeast biomass coatings under high elemental Fe concentration, with increased formation of chlamydospores that accumulate a red pigment-insoluble pulcherrimin rich in iron. Pulcherrimin in biomass is detected at both high and low elemental Fe concentrations, with the chemical binding of iron leading to sequestration of soluble Fe and accumulation of pulcherrimin in biomass chlamydospores.