In vitro inhibition of Saccharomyces cerevisiae growth by Metschnikowia spp. triggered by fast removal of iron via two ways.

Simple and convenient innovative assays in vitro demonstrating Metschnikowia spp. competition with Saccharomyces cerevisiae for an essential nutrient iron are presented. The tested Metschnikowia strains possess a common genetically determined property of secreting a pulcherriminic acid which in the presence of iron (III) ions forms an insoluble red pigment pulcherrimin. Both initial accumulation in growing Metschnikowia cells and subsequent precipitation in the form of pulcherrimin in the media contribute to iron removal by functioning cells. The predominant way depends on the strain. Due to fast elimination of iron, the growth of S. cerevisiae can be inhibited by tested Metschnikowia strains at concentrations of elemental iron in the media not exceeding 12 mg kg-1. Inhibition can be regulated by additional supply of microquantities of iron onto the surface of the solid medium within 20-24 h. At relatively low concentrations of elemental iron (below 1 mg kg-1), additional supplements of iron onto the surface provide an advancement in understanding the inhibition possibilities and enable the assay control. Microscopy observations revealed that Metschnikowia chlamydospores are involved in iron removal at relatively high iron concentrations. The results may find application in development of new methodologies and strategies for biocontrol or inhibition of pathogenic microorganisms.

The yeast community of Conotelus sp. (Coleoptera: Nitidulidae) in Brazilian passionfruit flowers (Passiflora edulis) and description of Metschnikowia amazonensis sp. nov., a large-spored clade yeast.

Species of the nitidulid beetle Conotelus found in flowers of Convolvulaceae and other plants across the New World and in Hawaii consistently harbour a yeast community dominated by one or more large-spored Metschnikowia species. We investigated the yeasts found in beetles and flowers of cultivated passionfruit in Rondônia state, in the Amazon biome of Brazil, where a Conotelus species damages the flowers and hinders fruit production. A sample of 46 beetles and 49 flowers yielded 86 and 83 yeast isolates, respectively. Whereas the flower community was dominated by Kodamaea ohmeri and Kurtzmaniella quercitrusa, the major yeasts recovered from beetles were Wickerhamiella occidentalis, which is commonly isolated from this community, and a novel species of large-spored Metschnikowia in the arizonensis subclade, which we describe here as Metschnikowia amazonensis sp. nov. Phylogenetic analyses based on barcode sequences (ITS-D1/D2) and a multigene alignment of 11,917 positions (genes ura2, msh6, and pmt2) agreed to place the new species as a sister to Metschnikowia arizonensis, a rare species known only from one locality in Arizona. The two form sterile asci when mated, which is typical of related members of the clade. The α pheromone of the new species is unique but typical of the subclade. The type of M. amazonensis sp. nov. is UFMG-CM-Y6309T (ex-type CBS 16156T , mating type a), and the designated allotype (mating type α) is UFMG-CM-Y6307A (CBS 16155A ). MycoBank MB 833560.