Hg tolerance and biouptake of an isolated pigmentation yeast Rhodotorula mucilaginosa

Copper Tolerance of Novel Rhodotorula sp. Yeast Isolated from Gold Mining Ore in Gia Lai, Vietnam

In this study, twenty-five yeast strains were isolated from soil samples collected in the gold mining ore in Gia Lai, Vietnam. Among them, one isolate named GL1T could highly tolerate Cu2+ up to 10 mM, and the isolates could also grow in a wide range of pH (3-7), and temperature (10-40 °C). Dried biomass of GL1 was able to remove Cu2+ effectively up to 90.49% with a maximal biosorption capacity of 18.1 mg/g at pH 6, temperature 30 °C, and incubation time 60 min. Sequence analysis of rDNA indicated this strain was closely related to Rhodotorula mucilaginosa but with 1.53 and 3.46% nucleotide differences in the D1/D2 domain of the 28S rRNA gene and the ITS1-5.8S rRNA gene-ITS2 region sequence, respectively. Based on phylogenetic tree analysis and the biochemical characteristics, the strain appears to be a novel Rhodotorula species, and the name Rhodotorula aurum sp. nov. is proposed. This study provides us with more information about heavy metal-tolerant yeasts and it may produce a new tool for environmental control and metal recovery operations.

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

Biotechnologically useful yeast strains have been receiving important attention worldwide for the demand of a wide range of industries. Rhodotorula mucilaginosa is recognized as a biotechnologically important yeast that has gained great interest as a promising platform strain, owing to the diverse substrate appetites, robust stress resistance, and other gratifying features. Due to its attractive properties, R. mucilaginosa has been regarded as an excellent candidate for the biorefinery of carotenoids, lipids, enzymes, and other functional bioproducts by utilizing low-cost agricultural waste materials as substrates. These compounds have aroused great interest as the potential alternative sources of health-promoting food products, substrates for so-called third-generation biodiesel, and dyes or functional ingredients for cosmetics. Furthermore, the use of R. mucilaginosa has rapidly increased as a result of advancements in fermentation for enhanced production of these valuable bioactive compounds. This review focuses on R. mucilaginosa in these advancements and summarizes its potential prospects as alternative sources of natural bioproducts.

Yeasts Inhabiting Extreme Environments and Their Biotechnological Applications

Yeasts are microscopic fungi inhabiting all Earth environments, including those inhospitable for most life forms, considered extreme environments. According to their habitats, yeasts could be extremotolerant or extremophiles. Some are polyextremophiles, depending on their growth capacity, tolerance, and survival in the face of their habitat’s physical and chemical constitution. The extreme yeasts are relevant for the industrial production of value-added compounds, such as biofuels, lipids, carotenoids, recombinant proteins, enzymes, among others. This review calls attention to the importance of yeasts inhabiting extreme environments, including metabolic and adaptive aspects to tolerate conditions of cold, heat, water availability, pH, salinity, osmolarity, UV radiation, and metal toxicity, which are relevant for biotechnological applications. We explore the habitats of extreme yeasts, highlighting key species, physiology, adaptations, and molecular identification. Finally, we summarize several findings related to the industrially-important extremophilic yeasts and describe current trends in biotechnological applications that will impact the bioeconomy.

Seasonal Variability of Photosynthetic Microbial Eukaryotes (<3 µm) in the Kara Sea Revealed by 18S rDNA Metabarcoding of Sediment Trap Fluxes

This survey is the first to explore the seasonal cycle of microbial eukaryote diversity (<3 µm) using the NGS method and a 10-month sediment trap (2018–2019). The long-term trap was deployed from September to June in the northwestern part of the Kara Sea. A water sample collected before the sediment trap was deployed and also analyzed. The taxonomic composition of microbial eukaryotes in the water sample significantly differed from sediment trap samples, characterized by a high abundance of Ciliophora reads and low abundance of Fungi while trap samples contained an order of magnitude less Ciliophora sequences and high contribution of Fungi. Photosynthetic eukaryotes (PEs) accounting for about 34% of total protists reads were assigned to five major divisions: Chlorophyta, Cryptophyta, Dinoflagellata, Haptophyta, and Ochrophyta. The domination of phototrophic algae was revealed in late autumn. Mamiellophyceae and Trebouxiophyceae were the predominant PEs in mostly all of the studied seasons. Micromonas polaris was constantly present throughout the September–June period in the PE community. The obtained results determine the seasonal dynamics of picoplankton in order to improve our understanding of their role in polar ecosystems.

Heavy Metal-Resistant Filamentous Fungi as Potential Mercury Bioremediators

Filamentous fungi native to heavy metals (HMs) contaminated sites have great potential for bioremediation, yet are still often underexploited. This research aimed to assess the HMs resistance and Hg remediation capacity of fungi isolated from the rhizosphere of plants resident on highly Hg-contaminated substrate. Analysis of Hg, Pb, Cu, Zn, and Cd concentrations by X-ray spectrometry generated the ecological risk of the rhizosphere soil. A total of 32 HM-resistant fungal isolates were molecularly identified. Their resistance spectrum for the investigated elements was characterized by tolerance indices (TIs) and minimum inhibitory concentrations (MICs). Clustering analysis of TIs was coupled with isolates’ phylogeny to evaluate HMs resistance patterns. The bioremediation potential of five isolates’ live biomasses, in 100 mg/L Hg²⁺ aqueous solution over 48 h at 120 r/min, was quantified by atomic absorption spectrometry. New species or genera that were previously unrelated to Hg-contaminated substrates were identified. Ascomycota representatives were common, diverse, and exhibited varied HMs resistance spectra, especially towards the elements with ecological risk, in contrast to Mucoromycota-recovered isolates. HMs resistance patterns were similar within phylogenetically related clades, although isolate specific resistance occurred. Cladosporium sp., Didymella glomerata, Fusarium oxysporum, Phoma costaricensis, and Sarocladium kiliense isolates displayed very high MIC (mg/L) for Hg (140–200), in addition to Pb (1568), Cu (381), Zn (2092–2353), or Cd (337). The Hg biosorption capacity of these highly Hg-resistant species ranged from 33.8 to 54.9 mg/g dry weight, with a removal capacity from 47% to 97%. Thus, the fungi identified herein showed great potential as bioremediators for highly Hg-contaminated aqueous substrates.

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.

Heavy Metal Tolerance of Novel Papiliotrema Yeast Isolated from Vietnamese Mangosteen

Three yeast strains (Hue-1, Hue-8, and Hue-19) with strong heavy metal tolerance were isolated from mangosteen from Hue city, Vietnam. They exhibited identical phenotype and phylogeny. Sequence analysis of the D1/D2 region of the LSU rRNA gene and the internal transcribed spacer (ITS) region demonstrated that the closest relative of these strains is Papiliotrema sp. with 2.12% and 3.55-3.7% divergence in the D1/D2 domain, and ITS domain, respectively. Based on the physiological, biochemical, and molecular data, the three strains belong to a novel species of Papiliotrema genus, for which the name Papiliotrema huenov sp. nov. is proposed. These strains are highly tolerant of heavy metals compared to other yeasts, being able to grow in the presence of 2 mM Pb (II), 2 mM Cd (II), and up to 5 mM Ni (II), but no growth was observed in the presence of 1 mM As (III).