Improvement in extracellular protease production by the marine antarctic yeast Rhodotorula mucilaginosa L7

Reusing wastewater from Coffea arabica processing to produce single-cell protein using Candida sorboxylosa: Optimizing of culture conditions

Coffee is a crop of significant socioeconomic importance, and the reuse of agri-food by-products and biowaste has great potential across several industries. Coffee wastewater (CWW) is a valuable resource containing essential nutrients that can be utilized by Candida sorboxylosa for single-cell protein (SCP) production. This utilization contributes to mitigating the negative impacts of agro-industrial waste. The optimization of culture conditions using the design of experiments (DoE) technique is crucial in understanding the environmental factors influencing metabolite production. In our study, the DoE technique was employed to analyze culture conditions, including room temperature, pH 8.4, agitation at 200 rpm, a headspace of 60% (v/v), and an inoculum of 0.75 DO600nm over 28-h period. This approach resulted in a remarkable SCP yield of 64.4% and dry cell weight (DCW) of 2.26 g/L. It is noteworthy that there is no literature reporting SCP production under alkaline pH conditions in yeast. Interestingly, our work demonstrated that an alkaline pH of 8.4 significantly influenced SCP production by C. sorboxylosa. The DoE technique proved to be an efficient statistical tool for optimizing culture conditions, offering several advantages, such as: (i) conducting cultures at room temperature to minimize unnecessary energy consumption; (ii) reducing the incubation time from 46 to 28 h, thereby enhancing overall productivity; (iii) achieving 1.7-fold increase in SCP yield compared to previous basal production levels.

Milk clotting enzymes from marine resources and their role in cheese-making: A mini review

With the continual increase in global cheese consumption, rennet, the traditional milk coagulant, is unable to meet the growing demand in cheese production. Although several proteases from other sources have been used for cheese-making, they suffer various shortcomings. The ocean is home to a huge and diverse range of life forms, which represent a vast potential source of proteases. Marine proteases have been isolated from a number of marine species, including sponge, jellyfish, seaweed and marine animals, and some have been shown to be suitable as milk-clotting enzymes for cheese making. This review summarizes the latest studies on rennet substitutes from marine resources and their role in cheese-making. The emphasis of the review is on the isolation and purification of the marine proteases, the biochemical characteristics of these enzymes, especially their caseinolytic and milk-clotting properties, as well as their cleavage sites on casein. Some of the marine proteases have been applied as milk-clotting agent in cheese-making, with the resultant production of cheese with comparable characteristics, including sensory characteristics, to calf rennet cheese. The review concludes by highlighting the challenges and opportunities for future research in the field.

Understanding the Basis of Occurrence, Biosynthesis, and Implications of Thermostable Alkaline Proteases

The group of hydrolytic enzymes synonymously known as proteases is predominantly most favored for the class of industrial enzymes. The present work focuses on the thermostable nature of these proteolytic enzymes that occur naturally among mesophilic and thermophilic microbes. The broad thermo-active feature (40-80 °C), ease of cultivation, maintenance, and bulk production are the key features associated with these enzymes. Detailing of contemporary production technologies, and controllable operational parameters including the purification strategies, are the key features that justify their industrial dominance as biocatalysts. In addition, the rigorous research inputs by protein engineering and enzyme immobilization studies add up to the thermo-catalytic features and application capabilities of these enzymes. The work summarizes key features of microbial proteases that make them numero-uno for laundry, biomaterials, waste management, food and feed, tannery, and medical as well as pharmaceutical industries. The quest for novel and/or designed and engineered thermostable protease from unexplored sources is highly stimulating and will address the ever-increasing industrial demands.

Diversity, Ecological Role and Biotechnological Potential of Antarctic Marine Fungi

The Antarctic Ocean is one of the most remote and inaccessible environments on our planet and hosts potentially high biodiversity, being largely unexplored and undescribed. Fungi have key functions and unique physiological and morphological adaptations even in extreme conditions, from shallow habitats to deep-sea sediments. Here, we summarized information on diversity, the ecological role, and biotechnological potential of marine fungi in the coldest biome on Earth. This review also discloses the importance of boosting research on Antarctic fungi as hidden treasures of biodiversity and bioactive molecules to better understand their role in marine ecosystem functioning and their applications in different biotechnological fields.

Optimization of protease production and sequence analysis of the purified enzyme from the cold adapted yeast Rhodotorula mucilaginosa CBMAI 1528

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A protease from a psychrotolerant yeast was characterized.

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Protease production was dependent on temperature and medium composition.

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Mass spectrometry analysis indicated that the protein belongs to the pepsin family.

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We propose that the enzyme reported here could be Rodothorulapepsin.

Enzymes from cold-adapted microorganisms are of high interest to industries due to their high activity at low and mild temperatures, which makes them suitable for their use in several processes that either require a supply of exogenous energy or involve the use of heat labile products. In this work, the protease production by the strain Rhodotorula mucilaginosa CBMAI 1528, previously isolated from the Antarctic continent, was optimized, and the purified enzyme analyzed. It was found that protease production was dependent on culture medium composition and growth temperature, being 20 °C and a culture medium containing both glucose and casein peptone (20 and 10 g/L, respectively) the optimal growing conditions in batch as well as in bioreactor. Moreover, mass spectrometry analysis revealed that the enzyme under study has a 100 % sequence identity with the deduced amino acid sequence of a putative aspartic protease from Rhodotorula sp. JG-1b (protein ID: KWU42276.1). This result was confirmed by the decrease of 95 % proteolytic activity by pepstatin A, a specific inhibitor of aspartic proteases. We propose that the enzyme reported here could be Rodothorulapepsin, a protein characterized in 1972 that did not have an associated sequence to date and has been classified as an orphan enzyme.

Glutaminase-free L-asparaginase production by Leucosporidium muscorum isolated from Antarctic marine-sediment

L-asparaginase (ASNase) is an essential drug in the treatment of acute lymphoblastic leukemia (ALL). Commercial bacterial ASNases increase patient survival, but the consequent immunological reactions remain a challenge. Yeasts ASNase is closer to human congeners and could lead to lower side effects. Among 134 yeast strains isolated from marine-sediments in King George Island, Antarctica, nine were L-asparaginase producing yeasts and glutaminase-free. Leucosporidium muscorum CRM 1648 yielded the highest ASNase activity (490.41 U.L^-1) and volumetric productivity (5.12 U.L^-1 h^-1). Sucrose, yeast extract and proline were the best carbon and nitrogen sources to support growth and ASNase production. A full factorial design analysis pointed the optimum media condition for yeast growth and ASNase yield: 20 g L^-1 sucrose, 15 g L^-1 yeast extract and 20 g L^-1 proline, which resulted in 4582.5 U L^-1 and 63.64 U L^-1 h^-1 of ASNase and volumetric productivity, respectively. Analysis of temperature, pH, inoculum and addition of seawater indicated the best condition for ASNase production by this yeast: 12-15 °C, pH 5.5-6.5 and seawater >25% (v/v). Inoculum concentration seems not to interfere. This work is pioneer on the production of ASNase by cold-adapted yeasts, highlighting the potential of these microbial resources as a source of glutaminase-free L-asparaginase for commercial purposes.

Production, characterization, and immobilization of protease from the yeast Rhodotorula oryzicola

The protease was produced extracellularly in submerged fermentation by the yeast Rhodotorula oryzicola using different sources of nitrogen and maximum activity (6.54 × 10^-3 U/mg) was obtained in medium containing 2% casein (w/v). Purification of the protease by gel filtration chromatography resulted in a 3.07-fold increase of specific protease activity. The optimal pH and temperature for enzyme activity were 6.51 and 63.04 °C, respectively. Incubation in the presence of some salts enhanced enzyme activity, which peaked under 0.01 M BaCl₂ . The enzyme retained about 90% of enzymatic activity at temperatures 50-60 °C. The commercially available enzyme carriers evaluated, silica gel, Celite 545, and chitosan effectively immobilized the protease. The enzyme immobilized in Celite 545 retained 73.53% of the initial activity after 15 reuse cycles. These results are quite promising for large-scale production and immobilization of protease from R. oryzicola, as the high operational stability of the immobilized enzyme lowers production costs in biotechnological applications that require high enzymatic activity and stability under high temperatures.

Microbiological and virulence aspects of Rhodotorula mucilaginosa

We aimed to characterize microbiologically clinical isolates of R. mucilaginosa isolated from colonization of a patient with chronic renal disease (CKD), as well as to evaluate their phylogeny, antifungal susceptibility, virulence, and pathogenicity in order to infer the potential to become a possible infective agent. For this study, two isolates of R. mucilaginosa from oral colonization of a CKD patient were isolated, identified and characterized by classical (genotypic and phenotypic) methods. Susceptibility to conventional antifungals was evaluated, followed by biofilm production, measured by different techniques (total biomass, metabolic activity, colony forming units and extracellular matrix quantification). Finally, the pathogenicity of yeast was evaluated by infection of Tenebrio molitor larvae. All isolates were resistant to azole and sensitive to polyenes and they were able to adhere and form biofilm on the abiotic surface of polystyrene. In general, similar profiles among isolates were observed over the observed periods (2, 24, 48 and 72 hours). Regarding extracellular matrix components of biofilms at different maturation ages, R. mucilaginosa was able to produce eDNA, eRNA, proteins, and polysaccharides that varied according to time and the strain. The death curve in vivo model showed a large reduction in the survival percentage of the larvae was observed in the first 24 hours, with only 40 % survival at the end of the evaluation. We infer that colonization of chronic renal patients by R. mucilaginosa offers a high risk of serious infection. And also emphasize that the correct identification of yeast is the main means for an efficient treatment.

The expression, secretion and activity of the aspartic protease MpAPr1 in Metschnikowia pulcherrima IWBT Y1123

Protease-secreting yeasts have broad biotechnological potential for application to various industrial processes, including winemaking. However, this activity is influenced by the yeast response to environmental factors such as nitrogen and protein sources, as are found in grape juice. In this study, the wine-relevant yeast Metschnikowia pulcherrima IWBT Y1123, with known protease-secreting ability, was subjected to different nitrogen-containing compounds to monitor their impact on protease secretion and activity. Protease activity increased above basal levels for haemoglobin-containing treatments, indicating an inductive influence of proteins. On the other hand, treatments containing both haemoglobin and assimilable nitrogen sources led to a delayed increase in protease activity and protein degradation, suggesting a nitrogen catabolite repression mechanism at work. Protease activity and expression were furthermore evaluated in grape juice, which revealed increased expression and activity levels over time as promising results for further investigations into the impact of this yeast on wine properties.

Marine Fungi: Biotechnological Perspectives from Deep-Hypersaline Anoxic Basins

Deep-sea hypersaline anoxic basins (DHABs) are one of the most hostile environments on Earth. Even though DHABs have hypersaline conditions, anoxia and high hydrostatic pressure, they host incredible microbial biodiversity. Among eukaryotes inhabiting these systems, recent studies demonstrated that fungi are a quantitatively relevant component. Here, fungi can benefit from the accumulation of large amounts of organic material. Marine fungi are also known to produce bioactive molecules. In particular, halophilic and halotolerant fungi are a reservoir of enzymes and secondary metabolites with valuable applications in industrial, pharmaceutical, and environmental biotechnology. Here we report that among the fungal taxa identified from the Mediterranean and Red Sea DHABs, halotolerant halophilic species belonging to the genera Aspergillus and Penicillium can be used or screened for enzymes and bioactive molecules. Fungi living in DHABs can extend our knowledge about the limits of life, and the discovery of new species and molecules from these environments can have high biotechnological potential.

Understanding the regulation of extracellular protease gene expression in fungi: a key step towards their biotechnological applications

The secretion of proteases by certain species of yeast and filamentous fungi is of importance not only for their biological function and survival, but also for their biotechnological application to various processes in the food, beverage, and bioprocessing industries. A key step towards understanding the role that these organisms play in their environment, and how their protease-secreting ability may be optimally utilised through industrial applications, involves an evaluation of those factors which influence protease production. The objective of this review is to provide an overview of the findings from investigations directed at elucidating the regulatory mechanisms underlying extracellular protease secretion in yeast and filamentous fungi, and the environmental stimuli that elicit these responses. The influence of nitrogen-, carbon-, and sulphur-containing compounds, as well as proteins, temperature, and pH, on extracellular protease regulation, which is frequently exerted at the transcriptional level, is discussed in particular depth. Protease-secreting organisms of biotechnological interest are also presented in this context, in an effort to explore the areas of industrial significance that could possibly benefit from such knowledge. In this way, the establishment of a platform of existing knowledge regarding fungal protease regulation is attempted, with the particular goal of aiding in the practical application of these organisms to processes that require secretion of this enzyme.

Victoriomyces antarcticus gen. nov., sp. nov., a distinct evolutionary lineage of the Cephalothecaceae (Ascomycota) based on sequence-based phylogeny and morphology

In this study, we propose a new genus, Victoriomyces, with a new species, Victoriomyces antarcticus, isolated from soil samples collected in Victoria Land, Antarctica. To determine its taxonomic status and evolutionary relationships, phylogenetic analysis was performed on DNA sequences from the nuclear 18S rRNA, 28S rRNA and the second largest subunit of RNA polymerase II (RPB2) genes. Victoriomyces antarcticus constitutes one well-supported distinct lineage within the Cephalothecaceae (family incertae sedis in Sordariomycetes), in which the only recognised asexual morphs belong to the genus Phialemonium and to Acremonium thermophilum. Victoriomyces antarcticus can be clearly distinguished from these taxa by means of DNA sequence analysis and its morphological traits that consist in having a Metarhizium-like asexual morph, dark red-coloured disk-like structures, immature bodies and the production of an intense red pigment in the growth media. Finally, we inferred the divergence time of V. antarcticus and the Cephalothecaceae using Bayesian analysis and secondary calibration. The holotype of V. antarcticus is FBL 165. The ex-type strain has been deposited as MUT 3686^T and CCF 6158^T. An additional strain of the species is FBL 577. The MycoBank number is MB 823713 for the genus and MB 823714 for the species.

Fungal Peritonitis Caused by Rhodotorula mucilaginosa in a CAPD Patient Treated with Liposomal Amphotericin B: A Case Report and Literature Review

Rhodotorula mucilaginosa is a ubiquitous yeast that may cause serious peritoneal dialysis (PD) infections. A 70-year-old man receiving continuous ambulatory peritoneal dialysis (CAPD) for 6 months presented with a PD infection caused by Rhodotorula mucilaginosa The patient was treated with intravenous liposomal amphotericin B. His peritoneal catheter was simultaneously removed and reinserted. To date, only 10 cases of Rhodotorula CAPD infections have been reported. Catheters, corticoids, cancer, and previous antibiotic therapy were the main risk factors for these infections. For most patients, the peritoneal catheter was removed, leading to a definitive transfer to hemodialysis. Along with flucytosine, amphotericin B is the main antifungal that is used. Both have a lower minimal inhibitory concentration (MIC), whereas fluconazole and caspofungin have the highest MICs. We highlighted the efficacy of liposomal amphotericin B associated with simultaneous withdrawal and reinsertion of a peritoneal catheter in a case of Rhodotorula peritonitis in a CAPD patient. Further studies are needed to evaluate the treatment of this condition.

Cold-adapted enzymes produced by fungi from terrestrial and marine Antarctic environments

Antarctica is the coldest, windiest, and driest continent on Earth. In this sense, microorganisms that inhabit Antarctica environments have to be adapted to harsh conditions. Fungal strains affiliated with Ascomycota and Basidiomycota phyla have been recovered from terrestrial and marine Antarctic samples. They have been used for the bioprospecting of molecules, such as enzymes. Many reports have shown that these microorganisms produce cold-adapted enzymes at low or mild temperatures, including hydrolases (e.g. α-amylase, cellulase, chitinase, glucosidase, invertase, lipase, pectinase, phytase, protease, subtilase, tannase, and xylanase) and oxidoreductases (laccase and superoxide dismutase). Most of these enzymes are extracellular and their production in the laboratory has been carried out mainly under submerged culture conditions. Several studies showed that the cold-adapted enzymes exhibit a wide range in optimal pH (1.0-9.0) and temperature (10.0-70.0 °C). A myriad of methods have been applied for cold-adapted enzyme purification, resulting in purification factors and yields ranging from 1.70 to 1568.00-fold and 0.60 to 86.20%, respectively. Additionally, some fungal cold-adapted enzymes have been cloned and expressed in host organisms. Considering the enzyme-producing ability of microorganisms and the properties of cold-adapted enzymes, fungi recovered from Antarctic environments could be a prolific genetic resource for biotechnological processes (industrial and environmental) carried out at low or mild temperatures.