Rhodotorula mucilaginosa—alternative sources of natural carotenoids, lipids, and enzymes for industrial use

Bioremediation of malachite green dye toxicity under optimized conditions by Rhodotorula mucilaginosa AUMC13567

The escalating impacts of human urbanization and rapid industrial development have resulted in a growing global demand for synthetic textile dyes. Malachite green (MG) dye is a hazardous chromatic compound predominantly utilized as a textile dye, exhibiting a strong affinity for the substrate to which it is applied. When diluted, it serves as antimicrobial agent for fungal and bacterial diseases in fish farms. However, the disposal of textile dyeing wastes pose significant environmental challenges, contaminating soil, surface water, and adversely affecting human health and aquatic life. R. mucilaginosa exhibits robust growth and resistance capabilities even under conditions of nutrient deficiency or external stress. This study focuses on optimizing the malachite green dye degradation ability of the yeast strain Rhodotorula mucilaginosa AUMC13567. The results reveal that the optimal conditions for maximum decolorization which was 100% at 50 mg/L dye concentration involve cultivating R. mucilaginosa on medium comprising distilled water with 3% glucose, 0.5% peptone, 0.3% malt extract, and 0.3% yeast extract under aerobic conditions at 37˚C for 12 h at 150 rpm. Gas Chromatography-Mass Spectrometry (GC/MS) analysis confirms the yeast's efficacy in degrading toxic MG dye complex compounds into simple harmless metabolites. Fourier Transform Infrared (FTIR) analyses show formation of novel compounds post the degradation of MG dye. Further research is advised to identify and characterize the specific enzymes or metabolic pathways implicated in MG dye degradation by R. mucilaginosa AUMC13567. Cytotoxicity tests carried out on three human cell lines, including colorectal cancer, head and neck cancer, and healthy skin fibroblast, demonstrating that decolorized MG solution produces safe products devoid of cytotoxicity on tested human cell lines.

Comparative Study of the Productive Parameters of Two Breeds of the Bombyx mori Silkworm Fed Rhodotorula glutinis Yeast

In this study, a comparative approach was used with the aim of filling the knowledge gap regarding the productive and economic parameters of two native B. mori silkworm breeds (Lines C and Z) fed with different diets, namely mulberry leaves alone and mulberry leaves with R. glutinis yeast at two different concentrations (1 × 109 and 1 × 107 CFU/mL). The trifactorial experiment was carried out with 600 silkworms during the fifth instar, with 300 for each breed and 50 larvae per rearing tray. The larvae were randomly assigned into three feeding groups, with two replicates: in the control group (C), the larvae received ordinary mulberry leaves; in the first experimental group (RG-1), the larvae were given mulberry leaves supplemented with R. glutinis yeast at a 1 × 107 concentration; and in the second experimental group (RG-2), the larvae received the same quantity of mulberry leaves as the C and RG-1 groups, but with R. glutinis yeast at a 1 × 109 concentration. Line C larvae in the RG-1 group revealed higher values for most of the productive traits assessed. There was a positive and significant correlation between the weights and lengths of the larvae and the silk gland, the silk gland and the shell, the cocoon and the pupae and the shell, and the shell and the pupa size (p < 0.001). The steady decline in the parameters at a higher concentration suggests that R. glutinis positively influences a number of silkworm growth features at a recommended dosage of 1 × 107; however, further research is required to more precisely identify the mechanisms involved.

Effect of Glycosidase Production by Rhodotorula mucilaginosa on the Release of Flavor Compounds in Fermented White Radish

Fermented vegetables are highly valued by consumers for their distinct flavors and rich nutritional content. Microbial fermentation imparts distinct flavors to these vegetables, with red yeast being a common microorganism involved in the fermentation process. However, studies on the impact of red yeast on flavor development in fermented vegetables remain scarce. This study employed multi-omics to analyze the effect of glycosidase produced by Rhodotorula mucilaginosa on the release of bound flavor compounds in vegetables. The results indicate that the yeast possesses multiple glycosidase-encoding genes, with the activities of α-galactosidase, β-glucosidase, and α-mannosidase being detected. Following the inoculation of yeast into fermented vegetable juice, a significant increase was observed in the expression of the β-glucosidase gene (bglX) and the α-glucosidase maltase gene (malL), alongside an increase in the content of flavor compounds correlated with the enzymatic activity detected. The application of commercial glycosidase to vegetable juice resulted in increased levels of cis-2-pentenol, hyacinthin, geranylacetone, and 1-dodecanol, consistent with findings from yeast-fermented vegetable juice. Thus, Rhodotorula mucilaginosa can secrete glycosidases that hydrolyze and release endogenous bound flavor compounds in vegetables, thereby enhancing the flavor quality of the final product.

New records of fungi in oleic ecosystems through analyzing olive oil, paste, and pomace from an olive oil production area in northern Italy

AIMS

This study analyzed the fungal diversity in oleic ecosystems adopting a culture-based approach.

METHODS AND RESULTS

In all, 66 yeasts and 10 filamentous fungi were isolated from samples of olive oil, paste, and pomace collected in a small area of olive oil production in northern Italy. Twenty-three and 7 taxa of yeasts and filamentous fungi were identified with molecular method, respectively. Most yeasts belonged to species commonly occurring in oleic. Conversely, other isolates belonged to species rarely or never found in olive oil and by-products. Filamentous fungal species were recorded for the first time on olive oil. The isolates were tested for β-glucosidase and esterase/lipase activity to evaluate their potential effects on the chemical and sensory properties of olive oil. Significant variations of these activities were observed among isolates.

CONCLUSIONS

Olive oil and its by-products can harbor significant variability among fungal species having enzymatic activities with potential impact on olive oil quality. The presence of basidiomycetous yeasts and filamentous fungi in stored oil requires further investigation.

Upcycling of Enzymatically Recovered Amino Acids from Textile Waste Blends: Approaches for Production of Valuable Second-Generation Bioproducts

Tremendous quantities of textile waste generated and primarily landfilled annually represent a huge risk of contaminating the environment, together with loss of valuable resources. Especially, blended fabrics further pose a challenge for recycling and valorization strategies, while enzymatic hydrolysis offers a highly specific and environmentally friendly solution. In this study, we demonstrate that proteases specifically hydrolyze the wool components in blends with polyester, allowing recovery of pure polyester fibers as well as amino acids and peptides as platform molecules for further valorization. Recovered amino acids and peptides were successfully used as a nitrogen source for cultivation of Chlorella vulgaris and Rhodotorula mucilaginosa for the production of valuable biomolecules including pigments and lipids. Here, 11.3 mg/gCDW chlorophyll and 47% lipid content were obtained from algal biomass, while 1.1 mg/gCDW carotenoids and 35% lipids content were reached from the yeast grown on wool hydrolysate as the sole nitrogen source. These could be applied as natural dyes for textile applications or as biofuels to replace toxic synthetic compounds and fossil resources, respectively. The presented concept demonstrates feasibility of enzymatic recovery and microbial valorization of components of blended textile waste to support the development toward a circular bioeconomy.

Single- vs. two-stage fermentation of an organic fraction of municipal solid waste for an enhanced medium chain carboxylic acids production - The impact of different pH and temperature

Single-stage fermentation was characterized by low medium chain carboxylic acids concentrations and different mesophilic temperatures had little effect on the process performance, whereas thermophilic conditions and pH 5.5 led to lactate and ethanol accumulation. Two-stage fermentation enabled almost twofold increase in the caproate productivity, that reached 0.8 g/L-d (1.7 ± 0.1 gCOD/L-d) with a caproate concentration of 4.0 g/L (8.4 gCOD/L) at specificity of 37% and led to a reduced release of carbon dioxide. Under pH 6.5 and temperature of 37°C the production of medium chain carboxylic acids required higher concentrations of ethanol. Number of genes annotated to fatty acid biosynthesis pathway exceeded the number of sequences assigned to the reverse β-oxidation pathway. Core microorganisms encoding these pathways belonged to Caproiciproducens, Caproicibacterium and Clostridium. This study provides a valuable insight for valorisation of organic fraction of municipal solid waste into carboxylates in a single- and two-stage systems.

Spatio-temporal distribution and biotechnological potential of culturable yeasts in the intertidal sediments and seawater of Aoshan Bay, China

Marine yeasts play a crucial role in marine microbial ecology, facilitating the biogeochemical cycling of carbon and nitrogen in marine ecosystems, while also serving as important reservoirs of bioactive compounds with extensive applications in pharmaceuticals, agriculture, and various industries. Intertidal flats, characterized by their complex ecological dynamics, are postulated to harbor a wealth of yeast resources. This study employed a culture-dependent approach to assess the diversity, spatio-temporal distribution, and biotechnological potential of yeast communities residing within the intertidal sediments and seawater of Aoshan Bay. A total of 392 yeast strains were identified from 20 distinct genera, encompassing 43 recognized species and four candidate novel species. Notably, 17 of these species were identified as novel occurrences in marine environments, underscoring the rich yeast biodiversity of the Aoshan Bay ecosystem, with Candida emerging as the dominant genus in both sedimentary and aqueous habitats. Yeast community composition exhibited significant spatial and temporal variation, with peak diversity and abundance observed in autumn, the subtidal zone, and the surface soil layer. No clear pattern, however, emerged linking these shifts to specific changes in community composition, highlighting the complex interactions between microbial communities, environmental variables, and anthropogenic disturbance. Although several yeast species isolated here have been previously recognized for their biotechnological potential, their diverse and abundant extracellular enzyme profiles were characterized, further highlighting their crucial role in organic matter decomposition and nutrient cycling within the tidal ecosystem, as well as their potential applicability in the food, fine chemical, textile, and pharmaceutical industries.IMPORTANCEThis study presents groundbreaking insights into the yeast diversity of Aoshan Bay, offering invaluable information on their spatial and temporal distribution patterns, as well as their biotechnological potential in the tidal environment. The findings reveal that the eutrophic intertidal flat is a rich repository of yeasts with abundant extracellular enzymatic activity and an important role in nutrient cycling and decomposition processes. Also, these yeasts serve as crucial indicators of ecosystem health and function and are excellent candidates for biotechnological and industrial applications. Collectively, this study not only expands our knowledge of the diversity and distribution of intertidal yeasts but also highlights their promising potential for biotechnological applications.

Introducing CCD1 into isolated Rhodotorula strain enhances flavor production and improves cigar fermentation

Introduction

The fermentation process plays an important role in enhancing the quality of cigar tobacco leaves. Through fermentation, microbial metabolism can degrade aromatic precursors and macromolecules, which increases the content of aroma compounds and reduces irritancy of tobacco leaves.

Methods

To further enhance the fermentation effect of cigar tobacco leaves, a Rhodotorula strain (Rh3), capable of producing carotenoids and improving fermentation quality, was isolated from cigar tobacco leaves. Subsequent genetic engineering techniques introduced the carotenoid cleavage dioxygenase 1 (CCD1) gene into the isolated Rh3.

Results

The modified Rh3 exhibits a significant increase in carotenoid degradation products compared with the original Rh3 in culture medium (from 0.29 μg/mg to 15 μg/mg). Subsequent cigar tobacco leaf fermentation experiments revealed that the modified Rh3 produced 65.9% more carotenoid degradation products compared to the control group, outperforming the original strain, which achieved a 41.4% increase. Furthermore, the modified strain preserves its ability to improve the intrinsic chemical composition of cigar tobacco leaves.

Discussion

We show here that modified Rh3 can increase the content of carotenoid degradation products, thereby enhancing the fermentation effect of cigar tobacco leaves. This study presents a beneficial exploration to improve the quality of cigar tobacco leaves for future use and offers a promising strategy for producing flavor compounds from discarded tobacco leaves.

In Rhodotorula mucilaginosa, active oxidative metabolism increases carotenoids to inactivate excess reactive oxygen species

Carotenoids produced by bacteria, yeasts, algae and plants inactivate Free Radicals (FR). However, FR may inactivate carotenoids and even turn them into free radicals. Oxidative metabolism is a source of the highly motile Reactive Oxygen Species (ROS). To evaluate carotenoid interactions with ROS, the yeast Rhodotorula mucilaginosa was grown in dextrose (YPD), a fermentative substrate where low rates of oxygen consumption and low carotenoid expression were observed, or in lactate (YPLac), a mitochondrial oxidative-phosphorylation (OxPhos) substrate, which supports high respiratory activity and carotenoid production. ROS were high in YPLac-grown cells and these were unmasked by the carotenoid production-inhibitor diphenylamine (DPA). In contrast, in YPD-grown cells ROS were almost absent. It is proposed that YPLac cells are under oxidative stress. In addition, YPLac-grown cells were more sensitive than YPD-grown cells to menadione (MD), a FR-releasing agent. To test whether carotenoids from cells grown in YPLac had been modified by ROS, carotenoids from each, YPD- and YPLac-grown cells were isolated and added back to cells, evaluating protection from MD. Remarkably, carotenoids extracted from cells grown in YPLac medium inhibited growth, while in contrast extracts from YPD-grown cells were innocuous or mildly protective. Results suggest that carotenoid-synthesis in YPLac-cells is a response to OxPhos-produced ROS. However, upon reacting with FR, carotenoids themselves may be inactivated or even become prooxidant themselves.

A New Method for Selective Extraction of Torularhodin from Red Yeast Using CO2-SFE Technique

Torularhodin is a dark pink colored carotenoid belonging to the xanthophylls group that can be biologically synthesized by red yeasts, especially by Rhodotorula and Sporobolomyces genera. The growing interest in this molecule is due to its biological activities such as antioxidant, anticholesterolemic, anti-inflammatory, antimicrobial, and anticancer. To satisfy potential commercial markets, numerous methods have been proposed to develop a cost-effective and environmentally friendly downstream process for the purification of torularhodin. However, obtaining high purity products without resorting to the use of toxic solvents, which can leave residues in the final preparations, remains a major challenge. In this context, the present study aimed to develop a new efficient method for the isolation of torularhodin from the red yeast Rhodotorula strain ELP2022 by applying the extraction technique with supercritical CO2 (CO2-SFE) in two sequential steps. In particular, in the first step, the dried lysed biomass of yeast was subjected to the action of CO2 in supercritical conditions (CO2SC) as sole solvent for extraction of apolar carotenoids. In the second step, the residual biomass was subjected to the action of CO2SC using ethanol as a polar co-solvent for the extraction of torularhodin. Both steps were carried out at different operating parameters of temperature (40 and 60 °C) and pressure (from 300 to 500 bar) with a constant CO2 flow of 6 L min-1. Regardless of the operating conditions used, this method allowed to obtain an orange-colored oily extract and a red-colored extract after the first and second step, respectively. In all trials, torularhodin represented no less than 95.2% ± 0.70 of the total carotenoids in the red extracts obtained from the second step. In particular, the best results were obtained by performing both steps at 40 °C and 300 bar, and the maximum percentage of torularhodin achieved was 97.9% ± 0.88. Since there are no data on the selective recovery of torularhodin from red yeast using the SFE technique, this study may be a good starting point to optimize and support the development of industrial production of torularhodin by microbial synthesis. This new method can significantly reduce the environmental impact of torularhodin recovery and can be considered an innovation for which an Italian patent application has been filed. In a circular bioeconomy approach, this method will be validated up to a pilot scale, culturing the strain Rhodotorula spp. ELP2022 on low-cost media derived from agri-food wastes.

Nitrogen limitation-induced adaptive response and lipogenesis in the Antarctic yeast Rhodotorula mucilaginosa M94C9

The extremotolerant red yeast Rhodotorula mucilaginosa displays resilience to diverse environmental stressors, including cold, osmolarity, salinity, and oligotrophic conditions. Particularly, this yeast exhibits a remarkable ability to accumulate lipids and carotenoids in response to stress conditions. However, research into lipid biosynthesis has been hampered by limited genetic tools and a scarcity of studies on adaptive responses to nutrient stressors stimulating lipogenesis. This study investigated the impact of nitrogen stress on the adaptive response in Antarctic yeast R. mucilaginosa M94C9. Varied nitrogen availability reveals a nitrogen-dependent modulation of biomass and lipid droplet production, accompanied by significant ultrastructural changes to withstand nitrogen starvation. In silico analysis identifies open reading frames of genes encoding key lipogenesis enzymes, including acetyl-CoA carboxylase (Acc1), fatty acid synthases 1 and 2 (Fas1/Fas2), and acyl-CoA diacylglycerol O-acyltransferase 1 (Dga1). Further investigation into the expression profiles of RmACC1, RmFAS1, RmFAS2, and RmDGA1 genes under nitrogen stress revealed that the prolonged up-regulation of the RmDGA1 gene is a molecular indicator of lipogenesis. Subsequent fatty acid profiling unveiled an accumulation of oleic and palmitic acids under nitrogen limitation during the stationary phase. This investigation enhances our understanding of nitrogen stress adaptation and lipid biosynthesis, offering valuable insights into R. mucilaginosa M94C9 for potential industrial applications in the future.

Biotechnological potential of red yeast isolated from birch forests in Poland

OBJECTIVES

This study aimed to isolate red yeast from sap, bark and slime exudates collected from Polish birch forests and then assessment of their biotechnological potential.

RESULTS

24 strains of red yeast were isolated from the bark, sap and spring slime fluxes of birch (Betula pendula). Strains belonging to Rhodotorula mucilaginosa (6), Rhodosporidiobolus colostri (4), Cystrofilobasidium capitaum (3), Phaffia rhodozyma (3) and Cystobasidium psychroaquaticum (3) were dominant. The highest efficiency of carotenoid biosynthesis (5.04 mg L-1) was obtained by R. mucilaginosa CMIFS 004, while lipids were most efficiently produced by two strains of P. rhodozyma (5.40 and 5.33 g L-1). The highest amount of exopolysaccharides (3.75 g L-1) was produced by the R. glutinis CMIFS 103. Eleven strains showed lipolytic activity, nine amylolytic activity, and only two proteolytic activity. The presence of biosurfactants was not found. The growth of most species of pathogenic moulds was best inhibited by Rhodotorula yeasts.

CONCLUSION

Silver birch is a good natural source for the isolation of new strains of red yeast with wide biotechnological potential.

Oleaginous fungi: a promising source of biofuels and nutraceuticals with enhanced lipid production strategies

Oleaginous fungi have attracted a great deal of interest for their potency to accumulate high amounts of lipids (more than 20% of biomass dry weight) and polyunsaturated fatty acids (PUFAs), which have a variety of industrial and biological applications. Lipids of plant and animal origin are related to some restrictions and thus lead to attention towards oleaginous microorganisms as reliable substitute resources. Lipids are traditionally biosynthesized intra-cellularly and involved in the building structure of a variety of cellular compartments. In oleaginous fungi, under certain conditions of elevated carbon ratio and decreased nitrogen in the growth medium, a change in metabolic pathway occurred by switching the whole central carbon metabolism to fatty acid anabolism, which subsequently resulted in high lipid accumulation. The present review illustrates the bio-lipid structure, fatty acid classes and biosynthesis within oleaginous fungi with certain key enzymes, and the advantages of oleaginous fungi over other lipid bio-sources. Qualitative and quantitative techniques for detecting the lipid accumulation capability of oleaginous microbes including visual, and analytical (convenient and non-convenient) were debated. Factors affecting lipid production, and different approaches followed to enhance the lipid content in oleaginous yeasts and fungi, including optimization, utilization of cost-effective wastes, co-culturing, as well as metabolic and genetic engineering, were discussed. A better understanding of the oleaginous fungi regarding screening, detection, and maximization of lipid content using different strategies could help to discover new potent oleaginous isolates, exploit and recycle low-cost wastes, and improve the efficiency of bio-lipids cumulation with biotechnological significance.

A screening method for plastic-degrading fungi

The growing amount of plastic waste requires new ways of disposal or recycling. Research into the biodegradation of recalcitrant plastic polymers is gathering pace. Despite some progress, these efforts have not yet led to technologically and economically viable applications. In this study, we show that respirometric screening of environmental fungal isolates in combination with scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy can be used to identify new strains with the potential for the degradation of plastic polymers. We screened 146 fungal strains, 71 isolated from car repair shops, an environment rich in long-chain hydrocarbons, and 75 isolated from hypersaline water capable of growing at high concentrations of NaCl. When grown in a minimal medium with no carbon source, some strains produced significantly more CO2 when a pure plastic polymer was added to the medium, some only at high salinity. A selection of these strains was shown by FTIR and Raman spectroscopy to alter the properties of plastic polymers: Cladosporium sp. EXF-13502 on polyamide, Rhodotorula dairenensis EXF-13500 on polypropylene, Rhodotorula sp. EXF-10630 on low-density polyethylene and Wickerhamomyces anomalus EXF-6848 on polyethylene terephthalate. Respirometry in combination with specific spectroscopic methods is an efficient method for screening microorganisms capable of at least partial plastic degradation and can be used to expand the repertoire of potential plastic degraders. This is of particular importance as our results also show that individual strains are only active against certain polymers and under certain conditions. Therefore, efficient biodegradation of plastics is likely to depend on a collection of specialized microorganisms rather than a single universal plastic degrader.

Enhancing Selenium Accumulation in Rhodotorula mucilaginosa Strain 6S Using a Proteomic Approach for Aquafeed Development

It is known that selenium (Se) is an essential trace element, important for the growth and other biological functions of fish. One of its most important functions is to contribute to the preservation of certain biological components, such as DNA, proteins, and lipids, providing protection against free radicals resulting from normal metabolism. The objective of this study was to evaluate and optimize selenium accumulation in the native yeast Rhodotorula mucilaginosa 6S. Sodium selenite was evaluated at different concentrations (5-10-15-20-30-40 mg/L). Similarly, the effects of different concentrations of nitrogen sources and pH on cell growth and selenium accumulation in the yeast were analyzed. Subsequently, the best cultivation conditions were scaled up to a 2 L reactor with constant aeration, and the proteome of the yeast cultured with and without sodium selenite was evaluated. The optimal conditions for biomass generation and selenium accumulation were found with ammonium chloride and pH 5.5. Incorporating sodium selenite (30 mg/L) during the exponential phase in the bioreactor after 72 h of cultivation resulted in 10 g/L of biomass, with 0.25 mg total Se/g biomass, composed of 25% proteins, 15% lipids, and 0.850 mg total carotenoids/g biomass. The analysis of the proteomes associated with yeast cultivation with and without selenium revealed a total of 1871 proteins. The results obtained showed that the dynamic changes in the proteome, in response to selenium in the experimental medium, are directly related to catalytic activity and oxidoreductase activity in the yeast. R. mucilaginosa 6S could be an alternative for the generation of selenium-rich biomass with a composition of other nutritional compounds also of interest in aquaculture, such as proteins, lipids, and pigments.

Bioproduction of yeast single cell oil with acute oral toxicity study intended for edible oil application

Human nutrition and health rely on edible oils. Global demand for edible oils is expanding, necessitating the discovery of new natural oil sources subjected to adequate quality and safety evaluation. However, in contrast to other agricultural products, India's edible oil supply is surprisingly dependent on imports. The microbial oil is generated by fermentation of oleaginous yeast Rhodotorula mucilaginosa IIPL32 MTCC 25056 using biodiesel plant byproduct crude glycerol as a fermentable carbon source. Enriched with monounsaturated fatty acid, nutritional indices mapping based on the fatty acid composition of the yeast SCO, suggested its plausible use as an edible oil blend. In the present study, acute toxicity evaluation of the yeast SCO in C57BL/6 mice has been performed by randomly dividing the animals into 5 groups with 50, 300, 2000, and 5000 mg/Kg yeast SCO dosage, respectively, and predicted the median lethal dose (LD50). Detailed blood biochemistry and kidney and liver histopathology analyses were also reported. The functions of the liver enzymes were also evaluated to check and confirm the anticipated toxicity. To determine cell viability and in vitro biocompatibility, the 3T3-L1 cell line and haemolysis tests were performed. The results suggested the plausible use of yeast SCO as an edible oil blend due to its non-toxic nature in mice models.

Molecular Basis of Yeasts Antimicrobial Activity-Developing Innovative Strategies for Biomedicine and Biocontrol

In the context of the growing concern regarding the appearance and spread of emerging pathogens with high resistance to chemically synthetized biocides, the development of new agents for crops and human protection has become an emergency. In this context, the yeasts present a huge potential as eco-friendly agents due to their widespread nature in various habitats and to their wide range of antagonistic mechanisms. The present review focuses on some of the major yeast antimicrobial mechanisms, their molecular basis and practical applications in biocontrol and biomedicine. The synthesis of killer toxins, encoded by dsRNA virus-like particles, dsDNA plasmids or chromosomal genes, is encountered in a wide range of yeast species from nature and industry and can affect the development of phytopathogenic fungi and other yeast strains, as well as human pathogenic bacteria. The group of the "red yeasts" is gaining more interest over the last years, not only as natural producers of carotenoids and rhodotorulic acid with active role in cell protection against the oxidative stress, but also due to their ability to inhibit the growth of pathogenic yeasts, fungi and bacteria using these compounds and the mechanism of competition for nutritive substrate. Finally, the biosurfactants produced by yeasts characterized by high stability, specificity and biodegrability have proven abilities to inhibit phytopathogenic fungi growth and mycelia formation and to act as efficient antibacterial and antibiofilm formation agents for biomedicine. In conclusion, the antimicrobial activity of yeasts represents a direction of research with numerous possibilities of bioeconomic valorization as innovative strategies to combat pathogenic microorganisms.

Challenges and prospects of yeast-based microbial oil production within a biorefinery concept

Biodiesel, unlike to its fossil-based homologue (diesel), is renewable. Its use contributes to greater sustainability in the energy sector, mainly by reducing greenhouse gas emissions. Current biodiesel production relies on plant- and animal-related feedstocks, resulting in high final costs to the prices of those raw materials. In addition, the production of those materials competes for arable land and has provoked a heated debate involving their use food vs. fuel. As an alternative, single-cell oils (SCOs) obtained from oleaginous microorganisms are attractive sources as a biofuel precursor due to their high lipid content, and composition similar to vegetable oils and animal fats. To make SCOs competitive from an economic point of view, the use of readily available low-cost substrates becomes essential. This work reviews the most recent advances in microbial oil production from non-synthetic sugar-rich media, particularly sugars from lignocellulosic wastes, highlighting the main challenges and prospects for deploying this technology fully in the framework of a Biorefinery concept.

Comparative Analysis of Capsular and Secreted Polysaccharides Produced by Rhodotorula mucilaginosa and Cryptococcus neoformans

Fungal infections are a global public health challenge, especially among immunocompromised patients. Basidiomycetous yeasts, such as Rhodotorula mucilaginosa, have emerged as opportunistic pathogens, but have received less attention than Cryptococcus neoformans. This study aimed to characterize the polysaccharides of R. mucilaginosa and compare them with those of C. neoformans, analyzing their clinical implications. Comprehensive physicochemical, mechanical, and ultrastructural analyses of polysaccharides from both species were performed, revealing correlations with virulence and pathogenicity. R. mucilaginosa cells are surrounded by a capsule smaller than that produced by C. neoformans, but with similar polysaccharides. Those polysaccharides are also secreted by R. mucilaginosa. Cross-reactivity with R. mucilaginosa was observed in a diagnostic C. neoformans antigen test, using both in vitro and in vivo samples, highlighting the need for more reliable tests. Some R. mucilaginosa strains exhibited virulence comparable to that of C. neoformans in an invertebrate experimental model (Tenebrio molitor). This study contributes to a deeper understanding of yeast pathogenicity and virulence, highlighting the need for more accurate diagnostic tests to improve the differential diagnosis of infections caused by basidiomycetous yeasts.

Rhodotorula mucilaginosa ZTHY2 Attenuates Cyclophosphamide-Induced Immunosuppression in Mice

Rhodotorula mucilaginosa (R. mucilaginosa) can enhance the immune and antioxidant function of the body. However, whether R. mucilaginosa has an immunoregulatory effect on cyclophosphamide (CTX)-induced immunosuppressed animals remains to be clarified. In this study, the R. mucilaginosa ZTHY2 that we isolated from the coastal waters of the South China Sea previously was prepared in order to investigate its immunoprotective effect on CTX-induced immunosuppression in mice, and the effects were compared to those of Lactobacillus acidophilus (LA) (a well-known probiotic). Seventy-two male SPF mice were divided into six groups: The C group (control); IM group (immunosuppressive model group) (+CTX); Rl, Rm, and Rh groups (+CTX+low, medium, and high concentration of R. mucilaginosa, respectively); and PC (positive control) group (+CTX+LA). After a 28-day feeding trial, blood samples were taken for biochemical and serum immunological analysis, and the thymus and spleen were collected to analyze the organ index, lymphocyte proliferation and differentiation, and antioxidant capacity. The findings showed that R. mucilaginosa ZTHY2 improved the spleen and thymus indices, effectively attenuated immune organ atrophy caused by CTX, and enhanced the proliferation of T and B lymphocytes induced by ConA and LPS. R. mucilaginosa ZTHY2 promoted the secretion of cytokines and immunoglobulins and significantly increased the contents of IL-2, IL-4, IL-6, TNF-α, IFN-γ, IgA, IgG, IgM, CD4, CD8, CD19, and CD20 in serum. The proportion of CD4+, CD8+, CD19+, and CD20+ lymphocytes in spleen, thymus, and mesenteric lymph nodes were increased. In addition, R. mucilaginosa ZTHY2 reduced the reactive oxygen species (ROS) and malondialdehyde (MDA) levels and increased glutathione (GSH), total superoxide dismutase (SOD), and catalase (CAT) levels. Our results indicated that R. mucilaginosa ZTHY2 can significantly enhance the immune function of immunosuppressed mice, and improving antioxidant capacity thus attenuates CTX-induced immunosuppression and immune organ atrophy.

Lignocellulosic biorefineries as a platform for the production of high-value yeast derived pigments - A review

Lignocellulosic byproducts, mainly generated by the agro-industrial sector, have great potential as cost-effective feedstocks for bioprocesses because of their abundant availability and high content of sugar-rich and nutrient-rich elements. This biomass can be employed as a carbon source to produce various molecules using several microorganisms. Yeast strains have shown their capability to metabolize diverse C5 and C6 carbon sources, thereby facilitating their use in the bioprocessing of lignocellulosic biomass. Furthermore, yeasts can produce a wide range of valuable products, including biofuels, enzymes, proteins, and pigments, making them attractive for use in integrated biorefineries. Yeast-derived pigments have versatile applications and are environmentally friendly alternatives to their synthetic counterparts. This review emphasizes the potential of lignocellulosic biomass as a feedstock for producing yeast-derived products with a focus on pigments as valuable molecules. It also proposes a yeast-derived pigment platform utilizing lignocellulosic byproducts and explores its potential integration in biorefineries.

Fungistatic Effect of Phthalide Lactones on Rhodotorula mucilaginosa

Currently, there is an increasing number of cases of fungal infections caused by opportunistic strains of the yeast Rhodotorula mucilaginosa, mainly in immunocompromised patients during hospitalization. The excessive use of antibiotics and azole compounds increases the risk of resistance to microorganisms. A new alternative to these drugs may be synthetic phthalide lactones with a structure identical to or similar to the natural ones found in celery plants, which show low toxicity and relatively high fungistatic activity. In the present study, the fungistatic activity of seven phthalide lactones was determined against R. mucilaginosa IHEM 18459. We showed that 3-n-butylidenephthalide, the most potent compound selected in the microdilution test, caused a dose-dependent decrease in dry yeast biomass. Phthalide accumulated in yeast cells and contributed to an increase in reactive oxygen species content. The synergistic effect of fluconazole resulted in a reduction in the azole concentration required for yeast inhibition. We observed changes in the color of the yeast cultures; thus, we conducted experiments to prove that the carotenoid profile was altered. The addition of lactones also triggered a decline in fatty acid methyl esters.

Rhodotorula sp. as a cell factory for production of valuable biomolecules

Rhodotorula sp. are well-known for their ability to biosynthesize a diverse range of valuable biomolecules, including carotenoids, lipids, enzymes, and polysaccharides. Despite the high number of studies conducted using Rhodotorula sp. at the laboratory scale, most of these do not address all processual aspects necessary for scaling up these processes for industrial applications. This chapter explores the potential of Rhodotorula sp. as a cell factory for the production of distinct biomolecules, with a particular emphasis on exploring their use from a biorefinery perspective. Through in-depth discussions of the latest research and insights into non-conventional applications, we aim to provide a comprehensive understanding of Rhodotorula sp.'s ability to produce biofuels, bioplastics, pharmaceuticals, and other valuable biochemicals. This book chapter also examines the fundamentals and challenges associated with the optimizing upstream and downstream processing of Rhodotorula sp-based processes. We believe that through this chapter, readers with different levels of expertise will gain insights into strategies for enhancing the sustainability, efficiency, and effectiveness of producing biomolecules using Rhodotorula sp.

Sustainable production of single-cell oil and protein from wastepaper hydrolysate: identification and optimization of a Rhodotorula mucilaginosa strain as a promising yeast

This study investigated the potential of wastepaper hydrolysate as a sustainable and low-cost carbon source for single-cell oil and protein production, attending to the growing need for alternative feedstocks and waste management strategies. Wastepaper, characterized by its high carbohydrate content, was subjected to enzymatic and chemo-enzymatic treatments for carbohydrate release. The chemo-enzymatic treatment performed better, yielding 65.3 g l-1 of fermentable sugars. A total of 62 yeast strains were screened for single-cell oil accumulation, identifying Rhodotorula mucilaginosa M1K4 as the most advantageous oleaginous yeast. M1K4 lipid production was optimized in liquid culture, and its fatty acid profile was analyzed, showing a high content of industrially valuable fatty acids, particularly palmitic (28%) and oleic (51%). Batch-culture of M1K4 in a 3-l reactor demonstrated the strain's ability to utilize wastepaper hydrolysate as a carbon source, with dry cell weight, total lipid and protein production of 17.7 g l-1, 4.5 g l-1, and 2.1 g l-1, respectively. Wastepaper as a substrate provides a sustainable solution for waste management and bioproduction. This research highlights the potential of R. mucilaginosa for lipid and protein production from wastepaper hydrolysate.