Search Results (87)

Coffee cherry pulp (CCP), a coffee by-product rich in pectin and phenolic compounds, serves as a valuable substrate for microbial enzyme production, improving the nutritional and antioxidant properties of poultry feed. This study evaluated the potential of Kluyveromyces marxianus ST5 to produce pectin-degrading enzymes using CCP. Under unoptimized conditions, the pectin lyase (PL) and polygalacturonase (PG) activities were 3.29 ± 0.22 and 6.32 ± 0.13 U/mL, respectively. Optimization using a central composite design (CCD) identified optimal conditions at 16.81% (w/v) CCP, 5.87% (v/v) inoculum size, pH 5.24, and 30 °C for 48 h, resulting in PL and PG activities of 9.17 ± 0.20 and 15.78 ± 0.14 U/mL, representing increases of 178.7% and 149.7% over unoptimized conditions. Fermented CCP was further evaluated using an in vitro chicken gastrointestinal digestion model. Peptide release increased by 66.2% compared with unfermented CCP. Antioxidant capacity also improved, with significant increases observed in DPPH (32.4%), ABTS (45.0%), and FRAP (42.3%) assays, along with an 11.1% increase in total phenolic content. These results demonstrate that CCP bioconversion by K. marxianus ST5 enhances digestibility and antioxidant properties, supporting its potential as a sustainable poultry feed additive and contributing to the valorization of agro-industrial waste. Full article

This study provides a comprehensive analysis of the microbial dynamics involved in the fermentation process of traditional Musalais wine, an intangible cultural heritage of Xinjiang. Utilizing metagenomic sequencing, we identified 2894 microbial species, of which 494 persisted throughout the fermentation process. Saccharomyces cerevisiae was the dominant species, with its prevalence increasing from 97.35% in the early phase to 99.38% in the mid phase, before slightly decreasing to 98.79% in the late phase. Additionally, 24 non-Saccharomyces yeast species, including Hanseniaspora uvarum, Lachancea thermotolerans, and Torulaspora delbrueckii, were detected. Common species associated with other fermented foods, including Wickerhamomyces anomalus, Kluyveromyces marxianus, Saccharomyces eubayanus, and Zygosaccharomyces parabailii, were also identified. Notably, species not previously used in food fermentation, such as Saccharomyces jurei, Sodiomyces alkalinus, Vanrija pseudolonga, and Moesziomyces antarcticus, were also identified in this study. Furthermore, the Kyoto Encyclopedia of Genes and Genomes (KO) and Gene Ontology (GO) revealed notable variations in metabolic pathways and enriched functional genes. In addition, a total of 82 volatile compounds were detected in the final product, with higher alcohols (60.12%), esters (37.80%), and organic acids (1.80%) being the most prevalent. These results offer important insights into microbial interactions and their influence on Musalais wine quality, laying the groundwork for optimizing the fermentation process. Full article

Biocontrol is one of the most promising alternatives to chemical preservatives for food preservation. This study investigated the biocontrol potential of yeasts isolated from raw milk cheese against spoilage moulds. Eighty-four native yeast strains were screened for antagonistic activity against Penicillium commune, Fusarium verticillioides, and Mucor plumbeus/racemosus via confrontation using a milk-based culture medium. Fifteen strains from the species Pichia jadinii, Kluyveromyces lactis, Kluyveromyces marxianus, and Geotrichum candidum exhibited significant antagonistic activity (inhibition zone > 2 mm) against M. plumbeus/racemosus and F. verticillioides. The modelling of the impact of ripening conditions revealed that temperature was the primary factor influencing yeast antagonism. In addition, notable variability at both species and strain levels was found. The antagonist activity was associated with different mechanisms depending on the species and strains. K. lactis stood out for its proteolytic activity and competition for iron and manganese. Additionally, two strains of this species (KL890 and KL904) were found to produce volatile organic compounds with antifungal properties (phenylethyl alcohol and 1-butanol-3-methyl propionate). G. candidum GC663 exhibited strong competition for space, as well as the ability to parasitise hyphae linked to its pectinase and β-glucanase activity. The latter enzymatic activity was detected in all P. jadinii strains, with P. jadinii PJ433 standing out due to its proteolytic activity. In a cheese matrix, the efficacy of eight yeast strains against three target moulds was assessed, highlighting the potential of G. candidum GC663 and P. jadinii PJ433 as biocontrol agents, exhibiting high and moderate efficacy, respectively, in controlling the growth of F. verticillioides and M. plumbeus/racemosus. Nonetheless, further research is necessary to elucidate their full spectrum of antifungal mechanisms and to validate their performance under industrial-scale conditions, including their impact on cheese quality. Full article

The vinasse from Agave americana L. (blue cabuya) liquor has a high concentration of organic matter, nutrients with high chemical oxygen demand (COD), and low pH, properties that give it the potential to generate adverse impact on the environment if improperly disposed of. In other countries, studies have been conducted on yeast strain combinations in vinasses to produce biomass and reduce organic load, but there are no studies of the aforementioned yeast consortium in blue cabuya liqueur vinasses to produce biomass and reduce COD. Given this problem, the objective of the research was to reduce this adverse environmental impact through aerobic fermentation of this vinasse with the yeast consortium Candida utilis, Kluyveromyces marxianus and Saccharomyces cerevisiae (D 47-Lalvin). As a result, biomass production and COD reduction were achieved. The study evaluated temperature variables of 28 °C, 30 °C, and 32 °C, and pH values of 3, 4, and 5 under conditions of consortium and nutrient diammonium phosphate (DAP) concentrations of 1.32 g/L and 1.5 g/L, respectively, in a bioreactor with automatic control of temperature, time, stirring speed of 100 RPM, and air flow of 1 VVM. The result was a biomass yield of 93.4% and a COD reduction of 33.3%. It is concluded that the aerobic fermentation process of blue cabuya liquor vinasse with the yeast consortium employed produces a high biomass yield, which can be used for its protein value as an animal feed supplement and, due to its low COD value, as an agricultural fertilizer. Full article

With rising multidrug-resistant yeast pathogens, conventional antifungals are becoming less effective, urging the need for adjuvants that enhance their activity at lower doses. This study evaluated the synergistic activity of antimicrobial peptidomimetics (TM8 and RK758) or colistin sulphate in combination with conventional antifungals against Candida albicans, C. tropicalis, C. parapsilosis, Meyerozyma guilliermondii, Nakaseomyces glabratus, Pichia kudriavzevii and Kluyveromyces marxianus, and Candidozyma auris using the checkerboard microdilution test. RK758 was synergistic with fluconazole in 78% of isolates, with the remaining 22% of isolates still showing partial synergy; it showed synergy with amphotericin B in 56% of isolates, and with caspofungin, 78% of isolates exhibited either synergy or partial synergy. TM8 showed synergy with fluconazole in 44% (with partial synergy in another 44%) of isolates, with amphotericin B in 67% of isolates, and with caspofungin in 44% (with partial synergy in another 44%) of isolates. Colistin with fluconazole or caspofungin exhibited synergy or partial synergy in 56% of the isolates. No antagonism was observed in any of the combinations. Additionally, a time-kill assay further demonstrated synergistic activity between fluconazole and TM8 or RK758. The effects of these peptidomimetics on cell membrane integrity were demonstrated in an ergosterol binding assay, supported by SYTOX Green and cellular leakage assays, both indicating a lytic effect. These results suggest that peptidomimetics can synergise with conventional antifungals, offering a potential strategy for combination therapy against yeast infections. The membrane lytic activity of the peptidomimetics likely plays a role in their synergistic interaction with antifungals, thereby enhancing the antimicrobial activities of both compounds at sub-MIC levels. Full article

Fermentation at high temperatures may be a viable alternative for ethanol production, especially in tropical climate regions. This work describes the evaluation of ethanol production through extractive fermentation at high temperatures using thermotolerant Kluyveromyces marxianus. An experimental design was applied to assess the effect of temperature on the ethanol removal process by CO₂ stripping. Subsequently, kinetic modeling of conventional batch ethanol fermentation at high temperatures was performed, and the hybrid Andrews−Levenspiel model was found to be suitable for describing the kinetics of this process. Experiments were conducted to evaluate ethanol production at high temperatures using thermotolerant yeast, specifically evaluating the effects of different specific CO₂ flow rates (ϕ = 1.0, 1.5, and 2.0 vvm) on ethanol stripping. The results indicated that in all the extractive fermentations conducted with K. marxianus, there was faster substrate uptake and earlier substrate exhaustion compared to conventional fermentation. Significant ethanol removal by stripping was achieved using a CO₂ flow rate of 1.0 vvm (EF_HT1), and complete substrate consumption was observed by the end of 12 h of fermentation. This result highlights the positive effect of temperature on ethanol entrainment. In addition, integrating the CO₂ stripping technique with high-temperature fermentation (T = 40 °C) improves process efficiency with a lower gas flow rate. This is advantageous, especially for industrial-scale applications, as it can reduce equipment costs associated with the CO₂ feed. Full article

This study evaluated Lolium perenne press juice as a sustainable substrate for Single-Cell Protein (SCP) production using Kluyveromyces marxianus. Key fermentation parameters were systematically optimized, including microbial reduction, dilution ratios, temperature, and nutrient supplementation. Pasteurization at 75 °C preserved essential nutrients better than autoclaving, resulting in a 27.8% increase in biomass yield. A 1:2 dilution of press juice enhanced fermentation efficiency, achieving 20.2% higher biomass despite a lower initial sugar content. Cultivation at 30 °C enabled sustained substrate utilization and outperformed 40 °C fermentation, increasing final biomass by 43.4%. Nutrient supplementation with yeast extract, peptone, and glucose led to the highest biomass yield, with a 71% increase compared to unsupplemented juice. Press juice from the tetraploid variety, Explosion, consistently outperformed the diploid Honroso, especially when harvested early, reaching up to 16.62 g·L⁻¹ biomass. Early harvests promoted faster growth, while late harvests exhibited higher biomass yield coefficients due to improved sugar-to-biomass conversion. Compared to a conventional YM medium, fermentation with L. perenne press juice achieved up to a threefold increase in biomass yield. These findings highlight the potential of grass-based substrates for efficient SCP production and demonstrate how agricultural parameters like variety and harvest timing influence both quantity and quality. The approach supports circular bioeconomy strategies by valorising underutilized biomass through microbial fermentation. Full article

The valorization of cheese whey, a rich by-product of the dairy industry that is rich in lactose (approx. 70%), proteins (14%), and minerals (9%), represents a promising approach for microbial fermentation. With global whey production exceeding 200 million tons annually, the high biochemical oxygen demand underlines the important need for sustainable processing alternatives. This review explores the biotechnological potential of whey as a fermentation medium by examining its chemical composition, microbial interactions, and ability to support the synthesis of valuable metabolites. Functional microorganisms such as lactic acid bacteria (Lactobacillus helveticus, L. acidophilus), yeasts (Kluyveromyces marxianus), actinobacteria, and filamentous fungi (Aspergillus oryzae) have demonstrated the ability to efficiently convert whey into a wide range of bioactive compounds, including organic acids, exopolysaccharides (EPSs), bacteriocins, enzymes, and peptides. To enhance microbial growth and metabolite production, whey fermentation can be carried out using various techniques, including batch, fed-batch, continuous and immobilized cell fermentation, and membrane bioreactors. These bioprocessing methods improve substrate utilization and metabolite yields, contributing to the efficient utilization of whey. These bioactive compounds have diverse applications in food, pharmaceuticals, agriculture, and biofuels and strengthen the role of whey as a sustainable biotechnological resource. Patents and clinical studies confirm the diverse bioactivities of whey-derived metabolites and their industrial potential. Whey peptides provide antihypertensive, antioxidant, immunomodulatory, and antimicrobial benefits, while bacteriocins and EPSs act as natural preservatives in foods and pharmaceuticals. Also, organic acids such as lactic acid and propionic acid act as biopreservatives that improve food safety and provide health-promoting formulations. These results emphasize whey’s significant industrial relevance as a sustainable, cost-efficient substrate for the production of high-quality bioactive compounds in the food, pharmaceutical, agricultural, and bioenergy sectors. Full article

Kluyveromyces marxianus is a yeast that can be used as a microbial factory. However, little is known about its response to stress conditions. This work evaluated the response of this yeast against ethanol, acetic acid, isoamyl alcohol, and hydrogen peroxide as stress agents. Cytotoxicity assays were performed to assess the residual viability using a direct method (CFU counting) and an indirect method based on the reduction in MTT. Then, fermentation kinetics were performed at IC30 and IC50 for each stress factor to evaluate the effect of moderate and intense stress. This work is the first report presenting IC50 values for ethanol (21.82 g/L), acetic acid (1.19 g/L), isoamyl alcohol (2.74 g/L), and hydrogen peroxide (0.09 g/L) in K. marxianus. The IC50 values for the indirect method are between 3.7 and 68% higher than those for the direct method. Hydrogen peroxide and ethanol were the stress agents showing the highest overestimations. The results presented here demonstrated the overestimation of cell viability by the indirect method. Direct CFU counting is an adequate method to determine yeast viability during toxicity studies of chemical compounds. It was also established that ethanol and hydrogen peroxide have the highest toxicity against K. marxianus ITD-01005 during fermentation at concentrations equivalent to IC30 and IC50 of each stress agent. Full article

Kluyveromyces marxianus is an emerging yeast cell host for diverse products, but multiple-gene expression in K. marxianus faces challenges due to limited current knowledge of cis-regulatory elements and insertion loci. Our previous study transferred an alien Saccharomyces cerevisiae chromosome I (R1) into K. marxianus, resulting in the creation of the monochromosomal hybrid yeast KS-R1. All R1 genes were actively transcribed, providing a series of loci with varying transcriptional activities. Here, we explore the use of R1 as a novel platform for stable, multi-gene integration and expression. By deleting three essential K. marxianus genes while complementing their functions with orthologs on R1, we achieved stable propagation of R1 in the absence of selective pressure. We characterized several loci on R1 that exhibit stable transcriptional activities under various conditions. GFP inserted in place of genes at six such loci demonstrated varying expression levels. Strains with GFP at two loci exhibited significantly higher expression than those with GFP at a single locus. Furthermore, we replaced five R1 genes with disulfide bond formation genes from Pichia pastoris at distinct loci, resulting in the active expression of all five genes and significantly enhanced production of heterologous glucoamylases BadGLA and TeGlaA. Our findings demonstrate that alien chromosomes offer a stable and versatile platform for the coordinated expression of multiple heterologous genes, serving as valuable tools for metabolic engineering and synthetic biology. Full article

Lactic acid (LA) is a key chemical used in various industries, including food, pharmaceuticals, and bioplastics. Although traditionally produced using lactic acid bacteria, yeasts offer significant advantages, such as higher tolerance to acidic environments, a broader substrate range, and the potential for genetic and metabolic engineering. This review explores the potential use of Lachancea thermotolerans, Saccharomyces cerevisiae, Kluyveromyces marxianus, Kluyveromyces lactis, Candida utilis, and Pichia kudriavzevii as LA producers, highlighting their unique characteristics and industrial applications. S. cerevisiae stands out due to its robust genetic toolkit and acid tolerance, while K. marxianus offers thermotolerance and the efficient utilization of lactose and pentoses, making it ideal for high-temperature fermentations. K. lactis is particularly suited for valorizing dairy by-products like whey, P. kudriavzevii exhibits high tolerance to multiple stresses, while C. utilis demonstrates superior resilience to lignocellulosic inhibitors, enabling its use in biorefineries. Key challenges, including enhancing LA tolerance and optimizing metabolic pathways, are addressed through strategies like heterologous lactate dehydrogenase (LDH) expression, redox balance modification, and adaptive laboratory evolution. The review also discusses industrial applications, particularly in the context of circular economy approaches, where yeasts can convert waste streams into high-value LA. Future research should focus on integrating yeasts into scalable, sustainable bioprocesses to meet the growing demand for renewable and biodegradable materials. Full article

One of the most unique non-conventional yeasts, Kluyveromyces marxianus, is rapidly gaining ground in biotechnology applications. K. marxianus possesses fast growth, thermotolerance, and a Crabtree-negative metabolism, features with a clear advantage over conventional yeasts like Saccharomyces cerevisiae. Additionally, it is diverse in carbon sources, utilizing lactate and xylose as well as lignocellulosic materials, which becomes critical in waste-utilizing and sustainable production industries. Besides the fact that K. marxianus has been useful in the production of valuable metabolites like β-galactosidase, ethanol, aroma compounds, and organic acids, its GRAS (Generally Recognized as Safe) designation makes K. marxianus a prime candidate for pharmaceutical and nutraceutical applications. This review summarizes a detailed description of K. marxianus’s biochemical and genetic features, its present applications, and future unexplored potentials such as probiotic development, vaccine production, bioremediation, and anticancer therapies. We also describe genetic tools that have been developed with improved metabolic pathways useful for new industry applications, making K. marxianus a resource in modern biotechnology. In sum, due to its unique features, K. marxianus appears to be a perfect alternative for areas such as biofuel production, biochemical synthesis, enzyme manufacturing, the dairy industry, and pharmaceuticals. Full article

There is an increasing interest in yeasts isolated from natural sources to be used as probiotics. Saccharomyces-based probiotics have been proposed as a valid alternative to the conventional drug therapy for the prevention and treatment of vulvovaginal candidiasis, also considering the resistance of some Candida strains to many antifungals. Here, we isolated from an artisanal sourdough a new yeast strain which was identified as Kluyveromyces marxianus and assessed its probiotic and safety properties, which resulted in comparable properties to all those exhibited by the commercial probiotic Saccharomyces boulardii. Then, we checked the antagonistic activity of the new isolate against some clinical fluconazole resistant C. albicans strains, showing its ability to inhibit filamentation, biofilm formation, and the adhesion of C. albicans to vaginal epithelial A-431 cells. Also, K. marxianus reduced the cell damage provoked by C. albicans and the expression of SAP2 and SAP6 genes. On the whole, our results enlarge the spectrum of the beneficial properties of the food-grade yeast K. marxianus showing for the first time its biotherapeutic potential against C. albicans. Full article

Kluyveromyces marxianus is a food-grade yeast known for its diverse beneficial traits, making it an attractive candidate for both food and biotechnology applications. This study explores the potential of Kluyveromyces marxianus as a promising alternative protein source for single-cell protein (SCP) production. Various Kluyveromyces strains were isolated and screened from traditional fermented dairy products, with Kluyveromyces marxianus NS127 identified as the most promising strain due to its superior growth characteristics, high SCP yield, and environmental tolerance. Notably, Kluyveromyces marxianus NS127 demonstrated significant substrate conversion capacity with a biomass yield of 0.63 g biomass/g molasses, achieving a dry biomass concentration of 66.64 g/L and a protein yield of 28.37 g/L. The protein extracted from the dry biomass exhibited excellent solubility (62.55%) and emulsification properties (13.15 m²/g) under neutral conditions, alongside high foaming stability (93.70–99.20%) across a broad pH range (3–11). These results underscore the potential of Kluyveromyces marxianus NS127 as a viable alternative protein source and provide a solid theoretical foundation for its industrial application. Full article

γ-Aminobutyric acid (GABA) is a valuable amino acid widely used in food, healthcare, and agriculture. GABA bioproduction by budding yeasts has been commonly reported, but related studies using non-conventional yeasts remain limited. In this study, two non-conventional natural yeast strains, namely, Kluyveromyces marxianus JMY140K and Metschnikowia reukaufii JMY075, were identified as promising GABA producers, and M. reukaufii JMY075 was discovered to be a GABA producer. Enhanced GABA production was observed in the two yeast strains under stress conditions, including high temperature and high ethanol and acetic acid levels. In particular, K. marxianus JMY140K showed 7.93 times higher GABA titers under thermal stress than that of the control. External stress conditions significantly influenced the GABA production of these two yeast strains. The culture filtrate of K. marxianus JMY140K also showed promising activities in human skin cells. In addition, K. marxianus JMY140K could also produce GABA using rice straw hydrolysate, which indicated that it has the potential to produce GABA using renewable biomass. Our studies provide insight for further enhancing the GABA production of natural yeasts and promoting its biotechnology applications. Full article