The Oleaginous Yeast Metschnikowia pulcherrima Displays Killer Activity against Avian-Derived Pathogenic Bacteria

Metschnikowia pulcherrima is a non-conventional yeast with potential to be used in biotechnological processes, especially those involving low-cost feedstock exploitation and biocontrol applications. The combination of traits that supports these industrial applications in M. pulcherrima also makes it an attractive option to study in the context of livestock health. In this study, we examined the specific interactions between M. pulcherrima and multiple avian pathogenic bacteria. We tested individual bacteria–yeast interactions and bacterial combinations in both solid and liquid media and in variable nutrient environments. Across multiple isolates of M. pulcherrima, we observed different levels of antimicrobial activity, varying from supporting the growth of competing bacteria through suppression and bacterial killing, and we found that these responses varied depending on the bacterial strains and media. We identified multiple molecular routes, including proteins produced by M. pulcherrima strains, that acted to control these microbial interactions. Furthermore, protein screening revealed that M. pulcherrima strains were induced to produce proteins specifically when exposed to bacterial strains, suggesting that fine-tuned mechanisms allow M. pulcherrima to function as a potential lynchpin in a microbial community.

Stability of Dry and Liquid Metschnikowia pulcherrima Formulations for Biocontrol Applications against Apple Postharvest Diseases

The yeast Metschnikowia pulcherrima is frequently isolated from environmental samples and has often been reported to exhibit strong antagonistic activity against plant pathogens. In order to assess the potential of this species for its development into a plant protection product, the survival during formulation and storage were quantified and field efficacy was assessed over a period of five years. Freeze dried and liquid M. pulcherrima formulations (i.e., with skim milk powder (SMP), sucrose, glycerol, xanthan, without additives) were prepared and the number of viable cells was quantified during storage at different temperatures. Field trials against apple postharvest diseases (Neofabreae) were performed with different dry formulations. M. pulcherrima proved exceptionally stable for many months and even years. Five years of field trials with the yeast revealed variable effects, but reduced Neofabreae infections of stored apples were observed in some years. M. pulcherrima applications after prior fungicide treatments repeatedly showed an additive effect as compared to the fungicide treatments alone. In summary, M. pulcherrima exhibited highly advantageous storage properties and encouraging activity against apple postharvest rots. Further studies to identify the factors responsible for antagonistic activity in the field and survival during storage are expected to lay the foundation for the future development of a plant protection product.

Chemical and Sensory Profiles of Merlot Wines Produced by Sequential Inoculation of Metschnikowia pulcherrima or Meyerzyma guilliermondii

Inoculation of selected non-Saccharomyces yeasts with Saccharomyces cerevisiae as means to produce Merlot wines with reduced ethanol contents was investigated. Fermentations of grape musts (25.4° Brix, pH 3.50, and 4.23 g/L titratable acidity) were conducted in stainless steel tanks inoculated with Metschnikowia pulcherrima strains P01A016 or NS-MP or Meyerozyma guilliermondii P40D002 with S. cerevisiae Syrah added after three days. After fermentation, wines with Mt. pulcherrima contained 13.8% (P01A016) or 13.9% (NS-MP) v/v ethanol, respectively, amounts which were lower than in wines with S. cerevisiae alone (14.9% v/v). Delayed inoculation of must with S. cerevisiae (day 3) or musts with My. guilliermondii contained elevated concentrations of ethyl acetate (145 and 148 mg/L, respectively), concentrations significantly higher than those with S. cerevisiae inoculated on day 0 or with either strain of Mt. pulcherrima. Descriptive sensory analysis revealed a significant effect due to panelist but not due to Mt. pulcherrima or My. guilliermondii. This research indicates the potential for commercial application of these yeasts towards the production of reduced alcohol wines but without imparting negative sensory attributes.

New Isolated Metschnikowia pulcherrima Strains from Apples for Postharvest Biocontrol of Penicillium expansum and Patulin Accumulation

Wild yeasts isolated from the surface of apples were screened for antagonistic activity against Penicillium expansum, the main producer of the mycotoxin patulin. Three antagonistic yeasts (Y33, Y29 and Y24) from a total of 90 were found to inhibit P. expansum growth. Identification by ITS region sequence and characterization showed that three selected isolates of yeast should be different strains of Metschnikowia pulcherrima. Several concentrations of the selected yeasts were used to study their in vitro antifungal effectivity against P. expansum on Petri dishes (plates with 63.6 cm2 surface) whereas their potential activity on patulin reduction was studied in liquid medium. Finally, the BCA that had the best in vitro antifungal capacity against P. and the best patulin degradation capacity was selected to be assessed directly on apples. All the selected strains demonstrated antifungal activity in vitro but the most efficient was the strain Y29. Isolated strains were able to reduce patulin content in liquid medium, Y29 being the only strain that completely reduced patulin levels within 120 h. The application of Y29 as biocontrol agent on the surface of apples inoculated with P. expansum, inhibited fungal growth and patulin production during storage. Therefore, the results shown that this yeast strain could be used for the reduction of P. expansum and its mycotoxin in apples or apple-based products by adapting the procedure application.

Heavy Metals Bioremediation and Water Softening Using Ureolytic Metschnikowia Pulcherrima and Raoultella Planticola Strains

This study employed the ureolytic fungal Metschnikowia pulcherrima (29A) and bacterial Raoultella planticola (VIP) strains in Pb 2+ and Hg 2+ removal using the promising CaCO 3 bio precipitation technique. Out of fifty isolates, strains 29A and VIP were selected based on their highest ureolytic activity followed by MIC assay using 350 ppm of Pb 2+ and Hg 2+ . The maximum urease activity recorded 884 and 639 U/mL for 29A and VIP strains at 24 and 30h of incubation, respectively. Complete removal of Pb 2+ was achieved at 42h and 90h for 29A, VIP correspondingly, while Hg 2+ was totally removed at 60h and 102h for 29A, VIP respectively. Remarkable removal of Ca 2+ (>95%) was achieved by the end of the experiments, which would address the hardness problem in the water treatment process. Further, EDX, SEM and, XRD were used to characterize the remediated precipitates. EDX profiles showed characteristic peaks of C, O and, Ca 2+ besides Pb 2+ and Hg 2+ . SEM illustrated the presence of microbial imprints and calcinated cells in the remediated bioliths. However, XRD confirmed the transformation of soluble metals to insoluble forms entrapped in calcite or vaterite lattice. Such a bioremediation approach ensures the detoxification and sequestration of heavy metals in a stable and durable matrix; obstructing their leach from carbonate complex trap to the environment.