Use of Waste Substrates for the Lipid Production by Yeasts of the Genus Metschnikowia-Screening Study

Pulcherrimin: a bio-derived iron chelate catalyst for base-free oxidation of 5-hydroxymethylfurfural to furandicarboxylic acid

This study explores the green and sustainable catalytic properties of pulcherrimin, a naturally occurring iron chelate, for the base-free oxidation of 5-hydroxymethylfurfural (5-HMF) to high-value products such as 2,5-furandicarboxylic acid (FDCA), a vital precursor for renewable bioplastics. Pulcherrimin, derived from Metschnikowia pulcherrima, selectively oxidised 5-HMF to 5,5-diformylfuran (DFF) at 100 °C, while at 120 °C, the oxidation proceeded efficiently to FDCA with a conversion of 73.3 ± 1.1%, and FDCA selectivity of 89.0 ± 1.9% under mild, base-free conditions. Adding a mild base enhanced overall conversion but diverted the reaction pathway towards 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), reducing the FDCA yield. The reusability of the pulcherrimin catalyst was tested over five reaction cycles, retaining a conversion activity of 59.1% and FDCA selectivity of 39.8%. These findings establish pulcherrimin as a promising, water-tolerant biocatalyst with potential environmental advantages, such as base-free operation and simplified product recovery, contributing to greener catalytic processes. Eliminating a homogenous base co-catalyst makes the process greener by avoiding the need for subsequent neutralisation steps while reducing environmental and economic costs.

The Effect of Temperature over the Growth and Biofilm Formation of the Thermotolerant Aspergillus flavus

Aspergillus flavus is a medically relevant fungus, particularly in tropical regions. Although its aflatoxin production and thermotolerance are well documented, its biofilm-forming ability has received less attention, despite being a key factor in the virulence of A. flavus as an opportunistic pathogen, which can significantly impact therapeutic outcomes. To investigate the influence of temperature on the growth and biofilm formation of an A. flavus isolate, we compared it on solid media with the reference strain A. flavus ATCC 22546 and documented morphological changes during conidial germination. We examined biofilm formation in both strains across different temperatures and evaluated the susceptibility of this A. flavus isolate to antifungal agents in both planktonic and biofilm form. Our results showed that the temperature can promote conidiation on solid media. Radial growth was highest at 28 °C, while the conidial count and density were favored at higher temperatures. Moreover, we determined that 37 °C was the optimal temperature for conidial germination and biofilm formation. We described four distinct phases in A. flavus biofilm development-initiation (0-12 h), consolidation (12-24 h), maturation (24-48 h), and dispersion (48-72 h)-with the notable presence of conidial heads at 42 °C. Carbohydrates and proteins constitute the primary components of the extracellular matrix. We observed an abundance of lipid droplets within the hyphae of the MMe18 strain biofilm. The mature biofilms demonstrated reduced susceptibility to amphotericin B and itraconazole, requiring higher inhibitory concentrations for both antifungals compared with their planktonic counterparts.

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.

Conversion of Mixed Waste Food Substrates by Carotenogenic Yeasts of Rhodotorula sp. Genus

The consequence of the massive increase in population in recent years is the enormous production of mainly industrial waste. The effort to minimize these waste products is, therefore, no longer sufficient. Biotechnologists, therefore, started looking for ways to not only reuse these waste products, but also to valorise them. This work focuses on the biotechnological use and processing of waste oils/fats and waste glycerol by carotenogenic yeasts of the genus Rhodotorula and Sporidiobolus. The results of this work show that the selected yeast strains are able to process waste glycerol as well as some oils and fats in a circular economy model and, moreover, are resistant to potential antimicrobial compounds present in the medium. The best-growing strains, Rhodotorula toruloides CCY 062-002-004 and Rhodotorula kratochvilovae CCY 020-002-026, were selected for fed-batch cultivation in a laboratory bioreactor in a medium containing a mixture of coffee oil and waste glycerol. The results show that both strains were able to produce more than 18 g of biomass per litre of media with a high content of carotenoids (10.757 ± 1.007 mg/g of CDW in R. kratochvilovae and 10.514 ± 1.520 mg/g of CDW in R. toruloides, respectively). The overall results prove that combining different waste substrates is a promising option for producing yeast biomass enriched with carotenoids, lipids, and beta-glucans.

Enhancing Red Yeast Biomass Yield and Lipid Biosynthesis by Using Waste Nitrogen Source by Glucose Fed-Batch at Low Temperature

This work reports the effect of simple feeding strategies and temperature to obtain high-cell-density cultures of Rhodotorula glutinis var. rubescens LOCKR13 maximizing the de novo lipid productivity using deproteinated potato wastewater (DPW) as a basic medium. Feeding DPW with glucose enables a high yield of Rhodotorula glutinis var. rubescens LOCKR13 biomass (52 g d.w. L−1) to be obtained. The highest values of lipid accumulation (34.15%, w/w), production (14.68 g L−1) and yield coefficients (YL/S: 0.242 g g−1), and volumetric productivity (PL: 0.1 g L−1 h−1) were reached by the strain in the two-stage fed-batch process at 20 °C. The lipid of yeast biomass was rich in oleic acid (Δ9C18:1) and palmitic acid (C16:0), and the lower temperature of incubation significantly increased the MUFA (especially oleic acid) content. For the first time, a unique set of thermal analyses of the microbial oil was performed. The isotherms of the oxidation kinetics (PDSC) showed that lipids extracted from the biomass of red yeast had high oxidative stability. This feature of the yeast oil can be useful for long-shelf-life food products and can be promising for the production of biodiesel.