Secondary metabolites and transcriptomic analysis of novel pulcherrimin producer Metschnikowia persimmonesis KIOM G15050: A potent and safe food biocontrol agent

Developing Bacillus subtilis as cell factory for the production of the natural biocontrol compound pulcherrimin

Pulcherrimin, a natural metabolite produced by Bacillus subtilis, demonstrates a range of biological activities, including its potential use as a natural antimicrobial, antioxidant, or coloring agent. PS832 was selected as the host cell from four B. subtilis strains. Transcriptome data revealed that the leucine pathway has minimal impact on pulcherrimin titer, whereas the enzymes encoded by the yvmC-cypX operon are essential for achieving high pulcherrimin production. Alleviating transcriptional repression of the yvmC-cypX operon led to an increase in pulcherrimin titer representing a 9.5-fold enhancement to 487 mg/l. The mutant BSP17 showed 65 % inhibition rate on a phytopathogen, revealing its potential as a biocontrol agent. Furthermore, optimizing iron concentration in the medium resulted in pulcherrimin titers of 610 mg/l in shake flasks and 811 mg/l in a 1.5-l bioreactor. It is the highest reported titer and sets the stage for further metabolic engineering to achieve industrial-scale production of pulcherrimin.

Unlocking the potential of Metschnikowia pulcherrima: a dive into the genomic and safety characterization of four plant-associated strains

Metschnikowia pulcherrima includes strains of applied agro-food interest, particularly due to the antimicrobial activity against plant pathogens, contribution to the aroma of fermented beverages, and preliminary evidence related to probiotic activity. This biotechnological relevance sheds new light of interest on the biology of this yeast. To better understand and expand its biotechnological potential and applicability, the genomes of M. pulcherrima NRRL Y-7111 T, NRRL Y-48695, CBS 10357, and NRRL Y-48712 were sequenced, and de-novo assembled. Between 10,671 and 14,548 genes were predicted and the cooperative genomic analyses were integrated with experimental assessments relating to traits relevant for biotechnological application and safety. In silico and in vitro safety assessment revealed intermediate sensitivity for itraconazole; furthermore, variants of the genes related to pulcherrimin production and transport were found in all the genomes. Moreover, an arsenal of carbohydrate-active enzymes (CAZymes) was unravelled, and their predicted localization was investigated. This study expands the body of knowledge on M. pulcherrima, including traits relevant for defining its safety as a bioresource, which is a pivotal aspect for its possible inclusion in the European Food Safety Authority (EFSA) Qualified Presumption of Safety (QPS) list and its application in REgulated food/feed PROducts (REPRO) both in the European Union & aligned European countries. KEY POINTS: • A pipeline for genomic characterisation and safety assessment of unconventional yeasts, using M. pulcherrima as a model species was developed. • M. pulcherrima strains can be considered safe and safety data can be used to develop a body of knowledge to include M. pulcherrima in EFSA QPS list. • Analysis of the predicted localization of CAZymes allowed the detection of compounds as potential biological control agents.

Advances and perspectives in biological control of postharvest fungal decay in citrus fruit utilizing yeast antagonists

Citrus fruits are one of the most highly grown fruit crops worldwide. A significant production problem, however, is their susceptibility to postharvest decay, caused by fungi such as Penicillium spp., resulting in significant losses in marketable yield. Some fungal species also produce mycotoxins that are potentially harmful to humans. Biological control of postharvest decay in citrus utilizing yeast antagonists has been shown to be a promising alternative to the use of synthetic fungicides to address increasingly stringent government regulatory policies and consumer demands. In this current review, we provide an overview of the research conducted on major postharvest decay fungi and their impact on the citrus industry. Then, the isolation and application of yeast antagonists used to manage postharvest decay in citrus is discussed, as well as their mechanisms of action, such as an oxidative burst of reactive oxygen species (ROS), iron depletion, and secondary metabolites. Lastly, the application of recent approaches (e.g., CRISPR/Cas9, RNAi, -omics technologies) in the study of citrus postharvest diseases is reviewed. For biological control to reach its full potential as a key component of an integrated disease management strategy for citrus, additional research will be required to explore the potential use of beneficial microbial consortia. The consortia will need to be comprised of individual core microbial species present in and on citrus fruit throughout its development and that metabolically complement each other in an interacting network.

Unforeseen current and future benefits of uncommon yeast: the Metschnikowia genus

Metschnikowia, the single-cell yeast form, is a genus of 85 species in the Saccharomycetales order that developed in both aquatic and terrestrial ecosystems after being found in 1899. This yeast is commonly used to control microbial populations in many biological and artificial conditions, such as fermentation. However, current study of Metschnikowia is limited to biological control features rather than researching on lucrative sectors such as beverage production, bioconversion manufacturing, cosmetics, and the pharmaceutical industry. This review summarizes numerous possible applications of Metschnikowia in human life, including potential secondary metabolites in industrial fields such as cosmetics and pharmaceuticals. Furthermore, Metschnikowia-yeast interaction is mentioned as a potential area for further exploration in terms of co-cultured microbes as biocontrol. Since Metschnikowia yeast arose in a variety of ecosystems, more discussion will be held regarding the interactions between Metschnikowia and their surroundings, particularly in fruits. Finally, the current regulatory challenges of Metschnikowia-based products are examined, and future research opportunities on Metschnikowia utilization are presented. KEY POINTS: • Utilization of Metschnikowia genus in various human aspects. • Promising secondary metabolites produced by Metschnikowia. • Challenge and opportunity on developing Metschnikowia-based products.

Photoprotective Effects of Yeast Pulcherrimin

Sunscreen products can protect the skin against the harmful effects of UV radiation, including reddening, aging, and cancer. The aim of this research was to evaluate the photoprotective effects of yeast pulcherrimin, an iron-chelating dipeptide. We first investigated the cytotoxicity of pulcherrimin produced by Metschnikowia pulcherrima yeast on the human keratinocyte HaCaT cell line, using the PrestoBlue assay. We assessed the ability of pulcherrimin to induce DNA repair after the exposure of HaCaT cells to oxidative stress. We also evaluated its protective activity against UVC radiation. The sun protective factor (SPF) was calculated using the Mansur equation. The UVA/UVB ratio values for pure pulcherrimin were evaluated using the Boots Star Rating system. The critical wavelength was determined by calculating the integrated optical density curve area. Based on the results, pulcherrimin shows strong cytoprotective effects through antioxidant and photoprotective activities on the HaCaT cell line. The calculated SPFs were 20 and 15 at pH = 7 and pH = 10, respectively. The critical wavelength above 370 nm and the UVA/UVB ratio R > 1 suggest that yeast pulcherrimin-a cyclic dipeptide containing iron-may be considered a promising photoprotective agent.