Extracellular enzymatic activities of basidiomycetous yeasts isolated from glacial and subglacial waters of northwest Patagonia (Argentina)

Enzymes and biosurfactants of industrial interest produced by culturable fungi present in sediments of Boeckella Lake, Hope Bay, north-east Antarctic Peninsula

This study characterized cultivable fungi present in sediments obtained from Boeckella Lake, Hope Bay, in the north-east of the Antarctic Peninsula, and evaluated their production of enzymes and biosurfactants of potential industrial interest. A total of 116 fungal isolates were obtained, which were classified into 16 genera within the phyla Ascomycota, Basidiomycota and Mortierellomycota, in rank. The most abundant genera of filamentous fungi included Pseudogymnoascus, Pseudeurotium and Antarctomyces; for yeasts, Thelebolales and Naganishia taxa were dominant. Overall, the lake sediments exhibited high fungal diversity and moderate richness and dominance. The enzymes esterase, cellulase and protease were the most abundantly produced by these fungi. Ramgea cf. ozimecii, Holtermanniella wattica, Leucosporidium creatinivorum, Leucosporidium sp., Mrakia blollopis, Naganishia sp. and Phenoliferia sp. displayed enzymatic index > 2. Fourteen isolates of filamentous fungi demonstrated an Emulsification Index 24% (EI24%) ≥ 50%; among them, three isolates of A. psychrotrophicus showed an EI24% > 80%. Boeckella Lake itself is in the process of drying out due to the impact of regional climate change, and may be lost completely in approaching decades, therefore hosts a threatened community of cultivable fungi that produce important biomolecules with potential application in biotechnological processes.

Degradation Potential of Xerophilic and Xerotolerant Fungi Contaminating Historic Canvas Paintings

Fungi are important contaminants of historic canvas paintings worldwide. They can grow on both sides of the canvas and decompose various components of the paintings. They excrete pigments and acids that change the visual appearance of the paintings and weaken their structure, leading to flaking and cracking. With the aim of recognizing the most dangerous fungal species to the integrity and stability of paintings, we studied 55 recently isolated and identified strains from historic paintings or depositories, including 46 species from 16 genera. The fungi were categorized as xero/halotolerant or xero/halophilic based on their preference for solutes (glycerol or NaCl) that lower the water activity (aw) of the medium. Accordingly, the aw value of all further test media had to be adjusted to allow the growth of xero/halophilic species. The isolates were tested for growth at 15, 24 °C and 37 °C. The biodeterioration potential of the fungi was evaluated by screening their acidification properties, their ability to excrete pigments and their enzymatic activities, which were selected based on the available nutrients in paintings on canvas. A DNase test was performed to determine whether the selected fungi could utilize DNA of dead microbial cells that may be covering surfaces of the painting. The sequestration of Fe, which is made available through the production of siderophores, was also tested. The ability to degrade aromatic and aliphatic substrates was investigated to consider the potential degradation of synthetic restoration materials. Xerotolerant and moderately xerophilic species showed a broader spectrum of enzymatic activities than obligate xerophilic species: urease, β-glucosidase, and esterase predominated, while obligate xerophiles mostly exhibited β-glucosidase, DNase, and urease activity. Xerotolerant and moderately xerophilic species with the highest degradation potential belong to the genus Penicillium, while Aspergillus penicillioides and A. salinicola represent obligately xerophilic species with the most diverse degradation potential in low aw environments.

Degradation of polypropylene by fungi Coniochaeta hoffmannii and Pleurostoma richardsiae

The urgent need for better disposal and recycling of plastics has motivated a search for microbes with the ability to degrade synthetic polymers. While microbes capable of metabolizing polyurethane and polyethylene terephthalate have been discovered and even leveraged in enzymatic recycling approaches, microbial degradation of additive-free polypropylene (PP) remains elusive. Here we report the isolation and characterization of two fungal strains with the potential to degrade pure PP. Twenty-seven fungal strains, many isolated from hydrocarbon contaminated sites, were screened for degradation of commercially used textile plastic. Of the candidate strains, two identified as Coniochaeta hoffmannii and Pleurostoma richardsiae were found to colonize the plastic fibers using scanning electron microscopy (SEM). Further experiments probing degradation of pure PP films were performed using C. hoffmannii and P. richardsiae and analyzed using SEM, Raman spectroscopy and Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR). The results showed that the selected fungi were active against pure PP, with distinct differences in the bonds targeted and the degree to which each was altered. Whole genome and transcriptome sequencing was conducted for both strains and the abundance of carbohydrate active enzymes, GC content, and codon usage bias were analyzed in predicted proteomes for each. Enzymatic assays were conducted to assess each strain's ability to degrade naturally occurring compounds as well as synthetic polymers. These investigations revealed potential adaptations to hydrocarbon-rich environments and provide a foundation for further investigation of PP degrading activity in C. hoffmannii and P. richardsiae.

Communities of culturable freshwater fungi present in Antarctic lakes and detection of their low-temperature-active enzymes

We evaluated the diversity and enzymatic activities of culturable fungi recovered from cotton baits submerged for 2 years in Hennequin Lake, King George Island, and from benthic biofilms in Kroner Lake, Deception Island, South Shetland Islands, maritime Antarctica. A total of 154 fungal isolates were obtained, representing in rank abundance the phyla Ascomycota, Basidiomycota and Mortierellomycota. Thelebolus globosus, Goffeauzyma sp., Pseudogymnoascus verrucosus and Metschnikowia australis were the most abundant taxa. The fungal community obtained from the biofilm was more diverse and richer than that recovered from the cotton baits. However, diversity indices suggested that the lakes may harbour further fungal diversity. The capabilities of all cultured fungi to produce the extracellular enzymes cellulase, protease, lipase, agarase, carrageenase, invertase, amylase, esterase, pectinase, inulinase and gelatinase at low temperature were evaluated. All enzymes were detected, but the most widely produced were protease and pectinase. The best enzymatic indices were obtained from Holtermanniella wattica (for invertase, esterase), Goffeauzyma sp. (amylase), Metschnikowia australis (protease), Mrakia blollopis (cellulase, pectinase), Pseudogymnoascus verrucosus (agarase, carrageenase) and Leucosporidium fragarium (inulinase). The detection of multiple enzymes reinforces the ecological role of fungi in nutrient cycling in Antarctic lakes, making nutrients available to the complex aquatic food web. Furthermore, such low-temperature-active enzymes may find application in different biotechnological processes, such as in the textile, pharmaceutical, food, detergent and paper industries, as well as environmental application in pollutant bioremediation processes.

An indigenous inland genotype of the black yeast Hortaea werneckii inhabiting the great pyramid of Giza, Egypt

Within the context of cultural heritage conservation, the biological study of tangible archeological sites is an important task to extend their existence and strengthen the transmission of their cultural value to future generations. In Egypt, a hyper-arid region, a microcolonial fungus with inky black growth was observed on a stone surface in the royal corridor of the Great Pyramid of Giza (King Khufu’s pyramid). The isolate was studied and characterized by microscopic morphometric measurements, evaluation of enzymatic activities, and genotyping techniques. The isolate was identified as Hortaea werneckii, a pleomorphic black yeast that naturally inhabits hypersaline environments and infects human skin. It has been reported from humid temperate, subtropical, and tropical zones, mainly from marine habitats and adjacent areas, and is associated with marine life. Since it was observed in an unusual habitat, it raises the question of its type and origin, whether environmental or clinical. The Egyptian Hortaea werneckii GPS5 isolate was profiled and characterized by adaptive extremophilic tolerance to arid salt stress, low portability to infect human skin, and the capability of solubilizing calcite; besides it was phylogenetically clustered with previous recorded environmental accessions. A profile that matches the biodeterioration fungal agents known as rock-inhabiting fungi, a potential threat to cultural heritage sites that requires attention and prevention plans.

From Glaciers to Refrigerators: the Population Genomics and Biocontrol Potential of the Black Yeast Aureobasidium subglaciale

Apples are affected by numerous fungi known as storage rots, which cause significant losses before and after harvest. Concerns about increasing antimicrobial resistance, bans on various fungicides, and changing consumer preferences are motivating the search for safer means to prevent fruit rot. The use of antagonistic microbes has been shown to be an efficient and environmentally friendly alternative to conventional phytopharmaceuticals. Here, we investigate the potential of Aureobasidium subglaciale for postharvest rot control. We tested the antagonistic activity of 9 strains of A. subglaciale and 7 closely related strains against relevant phytopathogenic fungi under conditions simulating low-temperature storage: Botrytis cinerea, Penicillium expansum, and Colletotrichum acutatum. We also investigated a selection of phenotypic traits of all strains and sequenced their whole genomes. The tested strains significantly reduced postharvest rot of apples at low temperatures caused by B. cinerea, C. acutatum (over 60%), and P. expansum (about 40%). Several phenotypic traits were observed that may contribute to this biocontrol capacity: growth at low temperatures, tolerance to high temperatures and elevated solute concentrations, and strong production of several extracellular enzymes and siderophores. Population genomics revealed that 7 of the 15 strains originally identified as A. subglaciale most likely belong to other, possibly undescribed species of the same genus. In addition, the population structure and linkage disequilibrium of the species suggest that A. subglaciale is strictly clonal and therefore particularly well suited for use in biocontrol. Overall, these data suggest substantial biological control potential for A. subglaciale, which represents another promising biological agent for disease control in fresh fruit.

IMPORTANCE After harvest, fruits are often stored at low temperatures to prolong their life. However, despite the low temperatures, much of the fruit is lost to rot caused by a variety of fungi, resulting in major economic losses and food safety risks. An increasingly important environmentally friendly alternative to conventional methods of mitigating the effects of plant diseases is the use of microorganisms that act similarly to probiotics—occupying the available space, producing antimicrobial compounds, and consuming the nutrients needed by the rot-causing species. To find a new microorganism for biological control that is particularly suitable for cold storage of fruit, we tested different isolates of the cold-loving yeast Aureobasidium subglaciale and studied their phenotypic characteristics and genomes. We demonstrated that A. subglaciale can significantly reduce rotting of apples caused by three rot-causing molds at low temperatures and thus has great potential for preventing fruit rot during cold storage.

Enological potential of non-Saccharomyces yeast strains of enological and brewery origin from Ukrainian Collection of Microorganisms

Non-conventional wine yeasts are extensively studied as promising producers of hydrolytic enzymes and as potential starter cultures in winemaking due to their ability to improve organoleptic properties of wine. Thirty-six yeast strains of enological and brewery origin from the Ukrainian Collection of Microorganisms belonging to Torulaspora, Kloeckera, Candida, Metschnikowia, Pichia, and Zygosaccharomyces genera have been screened for the production of extracellular hydrolases, stress tolerance, fermentative activity, and other traits of enological interest. This study revealed the high incidence of lipolytic, proteolytic, and β-glucosidase activities among the yeasts, while no pectinase activity was detected. Esterase, cellulase and glucanase activities were found in a small proportion of yeasts (8.33–16.66%). Several Pichia anomala, Kloekera javanica, Pichia membranifaciens, and Metschnikowia pulcherrima strains demonstrated a wide range of hydrolytic activities. High tolerance to stress factors (ethanol, osmotic, and oxidative stress) present during alcoholic fermentation was detected in P. anomala and M. pulcherrima strains. Fermentative activity of several yeast strains was evaluated in microfermentations in a model semi-synthetic medium. Strain P. anomala UCM Y-216 was selected as the most promising culture for winemaking due to its hydrolytic activities, tolerance to stress factors and other valuable metabolic traits. This study represents the first step for selecting a non-conventional yeast strain of enological origin as a potential co-culture for winemaking.

Removal of overpainting from an historical painting of the XVIII Century: A yeast enzymatic approach

Biocleaning of cultural heritage items is mainly performed using living microorganisms. Approaches utilizing the enzymes of isolated microorganisms have not been frequently investigated. To find an enzymatic alternative for the removal of an oil-based overpainting, we focused on the characterization and use of a yeast Extracellular Enzymatic Mixture (EEM). A historical silk yeast was selected for its lipolytic properties and its EEM was extracted after cultivation on a medium supplemented with linseed oil. The EEM protein content was visualized by SDS-PAGE, its concentration assessed by fluorimeter and the enzymatic activity evaluated by p-NPP spectrophotometric lipase assay. The yeast growth was suppressed by adding diverse metal ions (Cd, Zn, Cr and Cu) in Reasoner's 2A (R2A) broth, while the quantity and activity of EEM were affected by adding Fe and Pb. Various delivery systems (agar-agar, tylose and klucel G) alone or in a combination with EEM were assayed on the historical painting surface. The colorimetric measurements and the ATR-FTIR analysis indicated that the combinations tylose-EEM and klucel G-EEM can be easily and effectively applied as biocleaning procedures to remove oil-based overpainting from fragile and valuable historical painting surfaces.

L-asparaginase Production by Leucosporidium scottii in a Bench-Scale Bioreactor With Co-production of Lipids

L-asparaginase (ASNase) is a therapeutical enzyme used for treatment of acute lymphoblastic leukemia. ASNase products available in the market are produced by bacteria and usually present allergic response and important toxicity effects to the patients. Production of ASNase by yeasts could be an alternative to overcome these problems since yeasts have better compatibility with the human system. Recently, it was found that Leucosporidium scottii, a psychrotolerant yeast, produces ASNase. In order to advance the production of ASNase by this yeast, the present study aimed to select suitable process conditions able to maximize the production of this enzyme in a bench-scale bioreactor. Additionally, the accumulation of lipids during the enzyme production process was also determined and quantified. Experiments were carried out with the aim of selecting the most appropriate conditions of initial cell concentration (1.0, 3.5, and 5.6 g L^–1), carbon source (sucrose and glycerol, individually or in mixture) and oxygen transfer rate (k_La in the range of 1.42–123 h^–1) to be used on the production of ASNase by this yeast. Results revealed that the enzyme production increased when using an initial cell concentration of 5.6 g L^–1, mixture of sucrose and glycerol as carbon source, and k_La of 91.72 h^–1. Under these conditions, the enzyme productivity was maximized, reaching 35.11 U L^–1 h^–1, which is already suitable for the development of scale-up studies. Additionally, accumulation of lipids was observed in all the cultivations, corresponding to 2–7 g L^–1 (32–40% of the cell dry mass), with oleic acid (C_18:1) being the predominant compound (50.15%). Since the L-asparaginase biopharmaceuticals on the market are highly priced, the co-production of lipids as a secondary high-value product during the ASNase production, as observed in the present study, is an interesting finding that opens up perspectives to increase the economic feasibility of the enzyme production process.

Intra- and inter-cores fungal diversity suggests interconnection of different habitats in an Antarctic frozen lake (Boulder Clay, Northern Victoria Land)

A perennially frozen lake at Boulder Clay site (Victoria Land, Antarctica), characterized by the presence of frost mounds, have been selected as an in situ model for ecological studies. Different samples of permafrost, glacier ice and brines have been studied as a unique habitat system. An additional sample of brines (collected in another frozen lake close to the previous one) was also considered. Alpha- and beta-diversity of fungal communities showed both intra- and inter-cores significant (p < 0.05) differences, which suggest the presence of interconnection among the habitats. Therefore, the layers of frost mound and the deep glacier could be interconnected while the brines could probably be considered as an open habitat system not interconnected with each other. Moreover, the absence of similarity between the lake ice and the underlying permafrost suggested that the lake is perennially frozen based. The predominance of positive significant (p < 0.05) co-occurrences among some fungal taxa allowed to postulate the existence of an ecological equilibrium in the habitats systems. The positive significant (p < 0.05) correlation between salt concentration, total organic carbon and pH, and some fungal taxa suggests that a few abiotic parameters could drive fungal diversity inside these ecological niches.

The extremely halotolerant black yeast Hortaea werneckii - a model for intraspecific hybridization in clonal fungi

The polymorphic black yeast Hortaea werneckii (Capnodiales, Ascomycota) is extremely halotolerant (growth from 0 to 30% [w/v] NaCl) and has been extensively studied as a model for halotolerance in Eukaryotes for over two decades. Its most frequent sources are hypersaline environments and adjacent sea-water habitats in temperate, subtropical and tropical climates. Although typically saprobic, H. werneckii can also act as a commensal coloniser on human skin, causing tinea nigra on hands and soles. Here, we report that addition of NaCl to culture media expands the growth range of H. werneckii to 37 °C, which explains its colonisation of human skin, with its increased salinity. The morphological and physiological plasticity/ versatility of H. werneckii indicate that a species complex might be involved. This was investigated in this polyphasic taxonomic analysis based on the global diversity of H. werneckii strains collected from hypersaline environments, and from humans and animals. Analysis of D1/D2domains of 28S and internal transcribed spacer rDNA revealed 10 and 17 genotypes, respectively, that were not always compliant. The genotypes have global distributions. Human and environmental strains with the same genotypes are intermingled. Due to the limited number of phylogenetically informative characters in the ribosomal DNA dataset, the partial genes encoding for β-tubulin (BTB) and mini-chromosome maintenance protein (MCM7) were also sequenced. The use of these genes was hampered by ambiguous sequences obtained by Sanger sequencing, as a consequence of the diploid and highly heterozygous genome of many H. werneckii strains. Analysis of the BTB and MCM7 genes showed that in some cases two copies of the gene from the same genome are positioned in distant phylogenetic clusters of the intraspecific gene tree. Analysis of whole-genome sequences of selected H. werneckii strains generally confirmed the phylogenetic distances estimated on the basis of ribosomal genes, but also showed substantial reticulation within the phylogenetic history of the strains. This is in line with the hypothesis that the diploid genomes of H. werneckii were formed by hybridizations, which have sometimes occurred between relatively divergent strains.

Stress-Tolerant Yeasts: Opportunistic Pathogenicity Versus Biocontrol Potential

Stress-tolerant fungi that can thrive under various environmental extremes are highly desirable for their application to biological control, as an alternative to chemicals for pest management. However, in fungi, the mechanisms of stress tolerance might also have roles in mammal opportunism. We tested five species with high biocontrol potential in agriculture (Aureobasidium pullulans, Debayomyces hansenii, Meyerozyma guilliermondii, Metschnikowia fructicola, Rhodotorula mucilaginosa) and two species recognized as emerging opportunistic human pathogens (Exophiala dermatitidis, Aureobasidium melanogenum) for growth under oligotrophic conditions and at 37 °C, and for tolerance to oxidative stress, formation of biofilms, production of hydrolytic enzymes and siderophores, and use of hydrocarbons as sole carbon source. The results show large overlap between traits desirable for biocontrol and traits linked to opportunism (growth under oligotrophic conditions, production of siderophores, high oxidative stress tolerance, and specific enzyme activities). Based on existing knowledge and these data, we suggest that oligotrophism and thermotolerance together with siderophore production at 37 °C, urease activity, melanization, and biofilm production are the main traits that increase the potential for fungi to cause opportunistic infections in mammals. These traits should be carefully considered when assessing safety of potential biocontrol agents.

Habitat-specificity and diversity of culturable cold-adapted yeasts of a cold-based glacier in the Tianshan Mountains, northwestern China

Asian cold-based glacier yeasts with respect to their abundance, distribution, and taxonomy, in contrast to other continental cryosphere areas, have been little investigated. The present study reports the diversity and phylogeny of culturable cold-adapted yeasts in six cold habitats of the Glacier No.1 in the Tianshan Mountains (northwestern China). Of the total 591 yeast isolates, 401 were identified as basidiomycetous yeasts represented by 41 species of 15 genera, while 190 ascomycetous yeast isolates were assigned to the 8 species of 7 genera. The most prevalent species was Candida akabanensis with a 19.8% frequency of occurrence, followed by Vishniacozyma victoriae (16.4%) and Diutina rugosa (9.98%), of which V. victoriae was the only yeast species common to all six glacial habitats. Variability on the component and abundance of yeast taxa among glacial habitats primarily displayed in four dominant yeast genera, namely Candida, Vishniacozyma, Filobasidium, and Naganishia. However, network analysis illustrated that most of 32 rare yeast populations were habitat-specific, implying that the low-abundance yeast population was more easily influenced by the local habitat conditions (species sorting). Based on indicator species analyses, the subglacial habitat was characterized by psychrotolerant and/or psychrophilic yeast taxa.

Crop Rotation and Straw Application Impact Microbial Communities in Italian and Philippine Soils and the Rhizosphere of Zea mays

Rice is one of the most important nourishments and its cultivation binds large agricultural areas in the world. Its cultivation leads to huge water consumption and high methane emissions. To diminish these problems, crop rotation between paddy rice and maize is introduced in Asia, but can lead to losses of carbon and water by the formation of desiccation cracks. To counteract these problems rice straw can be applied. We analyzed soil microbial responses to different crop rotation systems [rice–rice (RR), maize–maize (MM), maize–rice (MR)] and to rice straw application in the soil and rhizosphere of maize. Zea mays was grown in microcosms using soils from different field locations, each including different crop rotation regimes. The bacterial and fungal community composition was analyzed by 16S rRNA gene and ITS based amplicon sequencing in the bulk soil and rhizosphere. The microbiota was clearly different in soils from the different field locations (analysis of similarity, ANOSIM: R = 0.516 for the bacterial community; R = 0.817 for the fungal community). Within the field locations, crop rotation contributed differently to the variation in microbial community composition. Strong differences were observed in communities inhabiting soils under monosuccession (RR vs. MM) (ANOSIM: R = 0.923 for the bacterial and R = 0.714 for the fungal community), while the communities in soils undergoing MR crop rotation were more similar to those of the corresponding RR soils (ANOSIM: R = 0.111–0.175). The observed differences could be explained by altered oxygen availabilities in RR and MR soils, resulting in an enrichment of anaerobic bacteria in the soils, and the presence of the different crops, leading to the enrichment of host-plant specific microbial communities. The responses of the microbial communities to the application of rice straw in the microcosms were rather weak compared to the other factors. The taxa responding in bulk soil and rhizosphere were mostly distinct. In conclusion, this study revealed that the different agricultural management practices affect microbial community composition to different extent, not only in the bulk soil but also in the rhizosphere, and that the microbial responses in bulk soil and rhizosphere are distinct.

Metagenomic analysis of orange colored protrusions from the muscle of Queen Conch Lobatus gigas (Linnaeus, 1758)

The endangered marine gastropod, Lobatus gigas, is an important fishery resource in the Caribbean region. Microbiological and parasitological research of this species have been poorly addressed despite its role in ecological fitness, conservation status and prevention of potential pathogenic infections. This study identified taxonomic groups associated with orange colored protrusions in the muscle of queen conchs using histological analysis, 454 pyrosequencing, and a combination of PCR amplification and automated Sanger sequencing. The molecular approaches indicate that the etiological agent of the muscle protrusions is a parasite belonging to the subclass Digenea. Additionally, the scope of the molecular technique allowed the detection of bacterial and fungi clades in the assignment analysis. This is the first evidence of a digenean infection in the muscle of this valuable Caribbean resource.

Degradation of organic pollutants mediated by extracellular peroxidase in simulated sunlit humic waters: A case study with 17β-estradiol

A growing body of research indicated that natural processes such as photolysis, biotransformation and sorption contribute to natural attenuation of organic compounds in natural waters. Here we report another potential natural reaction involving induction by extracellular peroxidase (POD) in sunlit humic waters. The degradation behavior of a natural estrogen 17β-estradiol (E2) in waters containing both horseradish peroxidase (HRP) and Suwannee River humic acid (SRHA) were studied under simulated sunlight. Significant enhancement of E2 degradation was observed in the presence of HRP as compared to direct and SRHA-inducted photolysis, resulting from the efficient degradation of E2 induced by HRP using photoproduced H₂O₂. The contribution of direct photolysis, indirect photolysis and enzymatic degradation to E2 degradation was calculated as 36.6, 31.7 and 31.7%, respectively. Lower yields of hydroxylation products and several new dimer products in E2+SRHA+HRP system relative to E2+SRHA system indicated that E2 degradation was primarily mediated by HRP, revealing the presence of HRP strongly affected the degradation pathway of E2. Take naturally occurring POD into consideration, enzymatic degradation may be an important attenuation pathway of E2 and other contaminants that are sensitive to peroxidases in certain waters such as humic rich freshwater system.

Aspergillus atacamensis and A. salisburgensis: two new halophilic species from hypersaline/arid habitats with a phialosimplex-like morphology

Halophilic fungal strains isolated from historical wooden staircase in a salt mine in Austria, and from wall biofilm and soil of a cave in the Coastal Range of the hyperarid Atacama Desert in Chile were characterised and described newly as Aspergillus salisburgensis and Aspergillus atacamensis. Morphological characters including solitary phialides producing solitary conidia and conidia in chains and/or heads suggested affinity to Aspergillus subgenus Polypaecilum. Strains required salt for growth, grew optimally on media with 10-25% NaCl and at 15-28 °C. These values are similar to those observed for Aspergillus salinarus comb. nov. (Phialosimplex salinarum), while the ex-type strains of Aspergillus sclerotialis, Aspergillus chlamydosporus and Aspergillus caninus (all belonging to Aspergillus subgen. Polypaecilum) grew optimally at 0-5% NaCl and showed fastest growth at 28-37 °C. Phylogenetic analyses on the basis of rDNA sequences, RAPD-PCR fingerprint patterns, and cellobiohydrolase gene (cbh-I) polymorphism clustered the strains into three groups and supported their taxonomic recognition as A. salinarus, A. atacamensis and A. salisburgensis. On the basis of phylogenetic inferences, also Sagenomella keratitidis is newly combined as Aspergillus keratitidis and inferred as a species of Aspergillus subgenus Polypaecilum.

Bioprospection of cold-adapted yeasts with biotechnological potential from Antarctica

The aim of this study was to investigate the ability to produce extracellular hydrolytic enzymes at low temperature of yeasts isolated from 25 de Mayo island, Antarctica, and to identify those exhibiting one or more of the evaluated enzymatic activities. A total of 105 yeast isolates were obtained from different samples and 66 were identified. They belonged to 12 basidiomycetous and four ascomycetous genera. Most of the isolates were ascribed to the genera Cryptococcus, Mrakia, Cystobasidium, Rhodotorula, Gueomyces, Phenoliferia, Leucosporidium, and Pichia. Results from enzymes production at low temperatures revealed that the Antarctic environment contains metabolically diverse cultivable yeasts, which represent potential tools for biotechnological applications. While most the isolates proved to produce 2-4 of the investigated exoenzymes, two of them evidenced the six evaluated enzymatic activities: Pichia caribbica and Guehomyces pullulans, which were characterized as psycrotolerant and psycrophilic, respectively. In addition, P. caribbica could assimilate several n-alkanes and diesel fuel. The enzyme production profile and hydrocarbons assimilation capacity, combined with its high level of biomass production and the extended exponential growth phase make P. caribbica a promising tool for cold environments biotechnological purposes in the field of cold-enzymes production and oil spills bioremediation as well.

Pectinolytic yeasts from cold environments: novel findings of Guehomyces pullulans, Cystofilobasidium infirmominiatum and Cryptococcus adeliensis producing pectinases

One hundred and three yeasts isolated from soil samples from King George Island and Tierra del Fuego province were screened in relation with their capability to produce pectinolytic enzymes. Although all the yeasts showed well-developed colonies at 20 °C, only eight showed a clear halo around the colony, indicative of pectin degradation. A secondary screening demonstrated that only four yeasts were capable to produce pectinases at low temperatures (8 °C). It could be seen that the selected yeasts were able to grow and produce high levels of polygalacturonase activity when submerged fermentations were performed using pectin-containing fruit wastes as substrates. None of the strains produced neither lyase nor rhamnogalacturonan hydrolase activities. Regarding pectin esterase activity, it was only produced in lower amounts by G. pullulans 8E (0.022 U ml^-1). A TLC analysis of the substrate cleavage pattern of the pectinolytic systems was consistent with an endo-type activity. The clarification of apple juice was only accomplished by G. pullulans pectinolytic system, with a clarification of 80% (%T₆₅₀) using 4 U/ml of enzyme at 20 °C. As far as we concern this work describes for the first time the production of pectinases by the cold-adapted yeasts species Cystofilobasidium infirmominiatum, Cryptococcus adeliensis and G. pullulans.

Identification and characterization of yeasts isolated from sedimentary rocks of Union Glacier at the Antarctica

The study of the yeasts that inhabit cold environments, such as Antarctica, is an active field of investigation oriented toward understanding their ecological roles in these ecosystems. In a great part, the interest in cold-adapted yeasts is due to several industrial and biotechnological applications that have been described for them. The aim of this work was to isolate and identify yeasts from sedimentary rock samples collected at the Union Glacier, Antarctica. Furthermore, the yeasts were physiologically characterized, including the production of metabolites of biotechnological interest. The yeasts isolated that were identified at the molecular level belonged to genera Collophora (1 isolate), Cryptococcus (2 isolates), Sporidiobolus (4 isolates), Sporobolomyces (1 isolate) and Torrubiella (2 isolates). The majority of yeasts were basidiomycetous and psychrotolerant. By cross-test assays for anti-yeast activity, it was determined that Collophora sp., Sporidiobolus salmonicolor, and Sporobolomyces roseus secreted a protein factor that kills Sporidiobolus metaroseus. The colored yeasts Sp. salmonicolor, Sp. metaroseus and Collophora sp. produced several carotenoid pigments that were identified as 2,3 dihydroxy-γ-carotene, -carotene, 4-ketotorulene, torulene β-cryptoxanthin and spirilloxanthin. Concerning analysis of mycosporines, these metabolites were only found in the yeasts Torrubiella sp. and Cryptococcus sp. T11-10-1. Furthermore, the yeasts were evaluated for the production of extracellular hydrolytic activities. Of the twelve activities analyzed, alkaline phosphatase, invertase, gelatinase, cellulase, amylase, and protease enzyme activities were detected. The yeasts Cryptococcus sp. T11-10-1 and Sporidiobolus metaroseus showed the highest number of different enzyme activities.

Purification and Characterization of a Novel Cold-Active Lipase from the Yeast Candida zeylanoides

Cold-active lipases have attracted attention in recent years due to their potential applications in reactions requiring lower temperatures. Both bacterial and fungal lipases have been investigated, each having distinct advantages for particular applications. Among yeasts, cold-active lipases from the genera Candida, Yarrowia, Rhodotorula, and Pichia have been reported. In this paper, biosynthesis and properties of a novel cold-active lipase from Candida zeylanoides isolated from refrigerated poultry meat are described. Heat-sterilized olive oil was found to be the best lipase biosynthesis inducer, while nonionic detergents were not effective. The enzyme was purified to homogeneity using hydrophobic chromatography and its enzymatic properties were tested. Pure enzyme activity at 7 °C was about 60% of the maximal activity at 27 °C. The enzyme had rather good activity at higher temperatures, as well. Optimal pH of pure lipase was between 7.3 and 8.2, while the enzyme from the crude extract had an optimum pH of about 9.0. The enzyme was sensitive to high ionic strength and lost most of its activity at high salt concentrations. Due to the described properties, cold-active C. zeylanoides lipase has comparative advantages to most similar enzymes with technological applications and may have potential to become an industrially important enzyme.

A Taxonomic Revision of the Wallemia sebi Species Complex

Wallemia sebi is a xerophilic food- and air-borne fungus. The name has been used for strains that prevail in cold, temperate and tropical climates. In this study, multi-locus phylogenetic analyses, using the internal transcribed spacer (ITS) regions, DNA replication licensing factor (MCM7), pre-rRNA processing protein (TSR1), RNA polymerase II largest subunit (RPB1), RNA polymerase II second largest subunit (RPB2) and a new marker 3´-phosphoadenosine-5´-phosphatase (HAL2), confirmed the previous hypothesis that W. sebi presents a complex of at least four species. Here, we confirm and apply the phylogenetic analyses based species hypotheses from a companion study to guide phenotypic assessment of W. sebi like strains from a wide range of substrates, climates and continents allowed the recognition of W. sebi sensu stricto and three new species described as W. mellicola, W. Canadensis, and W. tropicalis. The species differ in their conidial size, xerotolerance, halotolerance, chaotolerance, growth temperature regimes, extracellular enzyme activity profiles, and secondary metabolite patterns. A key to all currently accepted Wallemia species is provided that allow their identification on the basis of physiological, micromorphological and culture characters.

The diversity and extracellular enzymatic activities of yeasts isolated from water tanks of Vriesea minarum, an endangered bromeliad species in Brazil, and the description of Occultifur brasiliensis f.a., sp. nov

The diversity of yeast species collected from the bromeliad tanks of Vriesea minarum, an endangered bromeliad species, and their ability to produce extracellular enzymes were studied. Water samples were collected from 30 tanks of bromeliads living in a rupestrian field site located at Serrada Piedade, Minas Gerais state, Brazil, during both the dry and rainy seasons. Thirty-six species were isolated, representing 22 basidiomycetous and 14 ascomycetous species. Occultifur sp., Cryptococcus podzolicus and Cryptococcus sp. 1 were the prevalent basidiomycetous species. The yeast-like fungus from the order Myriangiales, Candida silvae and Aureobasidium pullulans were the most frequent ascomycetous species. The diversity of the yeast communities obtained between seasons was not significantly different, but the yeast composition per bromeliad was different between seasons. These results suggest that there is significant spatial heterogeneity in the composition of populations of the yeast communities within bromeliad tanks, independent of the season. Among the 352 yeast isolates tested, 282 showed at least one enzymatic activity. Protease activity was the most widely expressed extracellular enzymatic activity, followed by xylanase, amylase, pectinase and cellulase activities. These enzymes may increase the carbon and nitrogen availability for the microbial food web in the bromeliad tank of V. minarum. Sequence analyses revealed the existence of 10 new species, indicating that bromeliad tanks are important sources of new yeasts. The novel species Occultifur brasiliensis, f.a., sp. nov., is proposed to accommodate the most frequently isolated yeast associated with V. minarum. The type strain of O. brasiliensis, f.a., sp. nov. is UFMG-CM-Y375(T) (= CBS 12687(T)). The Mycobank number is MB 809816.

Basidioascus persicus sp. nov., a yeast-like species of the order Geminibasidiales isolated from soil

A novel species of basidiomycetes was isolated from kitchen garden soil in Shahryar city, Tehran province, Iran. Molecular and conventional methods were employed to identify and classify this single isolate. Morphologically, the isolate was considered yeast-like with hyaline and oval cells reproducing by monopolar budding, forming ballistoconidia, hyphae, arthroconidia and didymospores. Basidia and basidiospores resembling those produced by Basidioascus species were observed. Sequencing and Bayesian phylogenetic analysis of rRNA genes and the internal transcribed spacer region revealed its sister relationship to described species of the genus Basidioascus. Assimilation and fermentation tests, cell-wall carbohydrate analysis and enzyme activity tests were performed to provide insight into the metabolism of the isolate. Based on morphology, physiology and phylogeny of rRNA gene sequences, the isolate was shown to represent a novel species of the genus Basidioascus, described as Basidioascus persicus sp. nov. (holotype IBRC P1010180T = ex-type IBRC M30078T = isotype CBS 12808T). The MycoBank number of the novel species is MB 804703. An emended description of the genus Basidioascus is also provided.

Ecophysiological properties of cultivable heterotrophic bacteria and yeasts dominating in phytocenoses of Galindez Island, maritime Antarctica

Antarctic plants are stable specific microenvironments for microbial colonization that are still less explored. In this study, we investigated cultivable heterotrophic bacteria and yeasts dominating in plant samples collected from different terrestrial biotopes near Ukrainian Antarctic Base on Galindez Island, maritime Antarctica. Phylogenetic analysis revealed affiliation of the bacterial isolates to genera Pseudomonas, Stenotrophomonas, Brevundimonas, Sporosarcina, Dermacoccus, Microbacterium, Rothia and Frondihabitans, and the yeast isolates to genera Rhodosporidium, Cryptococcus, Leucosporidiella, Candida and Exophiala. Some ecophysiological properties of isolated strains were determined that are important in response to different stresses such as psychro- and halotolerance, UV-resistance and production of hydrolytic enzymes. The majority of isolates (88 %) was found to be psychrotolerant; all are halotolerant. Significant differences in survival subsequent to UV-C radiation were observed among the isolates, as measured by culturable counts. For the bacterial isolates, lethal doses in the range 80-600 J m⁻² were determined, and for the yeast isolates--in the range 300-1,000 J m⁻². Dermacoccus profundi U9 and Candida davisiana U6 were found as most UV resistant among the bacterial and yeast isolates, respectively. Producers of caseinase, gelatinase, β-glucosidase, and cellulase were detected. To the best of our knowledge, this is the first report on isolation of UV resistant strain D. profundi, and Frondihabitans strain from Antarctica, and on detection of cellulase activity in Antarctic yeast strain C. davisiana. The results obtained contribute to clarifying adaptation strategies of Antarctic microbiota and its possible role in functional stability of Antarctic biocenoses. Stress tolerant strains were detected that are valuable for ecological and applied studies.

Influence of abiotic variables on culturable yeast diversity in two distinct Alpine glaciers

The influence of some abiotic variables (pH, dry weight, organic carbon, nitrogen and phosphorous) on culturable yeast diversity in two distinct, but adjacent Alpine glaciers (Glacier du Géant, France, and Miage Glacier, Italy) was investigated. In all, 682 yeast strains were isolated and identified by D1/D2 and ITS sequencing as belonging to species of the genera Aureobasidium, Candida, Bulleromyces, Cryptococcus, Cystofilobasidium, Dioszegia, Guehomyces, Holtermanniella, Leucosporidiella, Mrakia, Mrakiella, Rhodotorula, Sporidiobolus, Sporobolomyces and Udenyomyces. Overall, the most represented genera were Cryptococcus (55% of isolates), Rhodotorula (17%) and Mrakia (10%). About 10% of strains, presumably belonging to new species (yet to be described), were preliminarily identified at the genus level. Principal component analysis (PCA) revealed that organic carbon, nitrogen and phosphorous are apparently mostly related to culturable yeast abundance and diversity. In this context, the hypothesis that the frequency of isolation of certain species may be correlated with some organic nutrients (with special emphasis for phosphorous) is discussed.

Diversity and extracellular enzymatic activities of yeasts isolated from King George Island, the sub-Antarctic region

Background

Antarctica has been successfully colonized by microorganisms despite presenting adverse conditions for life such as low temperatures, high solar radiation, low nutrient availability and dryness. Although these “cold-loving” microorganisms are recognized as primarily responsible for nutrient and organic matter recycling/mineralization, the yeasts, in particular, remain poorly characterized and understood. The aim of this work was to study the yeast microbiota in soil and water samples collected on King George Island.

Results

A high number of yeast isolates was obtained from 34 soil and 14 water samples. Molecular analyses based on rDNA sequences revealed 22 yeast species belonging to 12 genera, with Mrakia and Cryptococcus genera containing the highest species diversity. The species Sporidiobolus salmonicolor was by far the most ubiquitous, being identified in 24 isolates from 13 different samples. Most of the yeasts were psychrotolerant and ranged widely in their ability to assimilate carbon sources (consuming from 1 to 27 of the 29 carbon sources tested). All species displayed at least 1 of the 8 extracellular enzyme activities tested. Lipase, amylase and esterase activity dominated, while chitinase and xylanase were less common. Two yeasts identified as Leuconeurospora sp. and Dioszegia fristingensis displayed 6 enzyme activities.

Conclusions

A high diversity of yeasts was isolated in this work including undescribed species and species not previously isolated from the Antarctic region, including Wickerhamomyces anomalus, which has not been isolated from cold regions in general. The diversity of extracellular enzyme activities, and hence the variety of compounds that the yeasts may degrade or transform, suggests an important nutrient recycling role of microorganisms in this region. These yeasts are of potential use in industrial applications requiring high enzyme activities at low temperatures.

Cryptococcus species (Tremellales) from glacial biomes in the southern (Patagonia) and northern (Svalbard) hemispheres

Cryptococcus species (Basidiomycota) were isolated as the predominant yeast from glacial biomes of both Patagonia (Argentina) and the Svalbard archipelago (Norway). For a selected group of Cryptococcus belonging to Tremellales, assimilative profile, production of extracellular hydrolytic enzymes and ribosomal DNA internal transcribed spacer and large subunit (D1/D2) sequences were analysed. Cryptococcus victoriae, which was originally described from Antarctica, was the most frequently found species at both locations. High variability within the species was observed and described at the genotypic and phenotypic levels, two newly described species were found in both Patagonia and Svalbard: Cryptococcus fonsecae and Cryptococcus psychrotolerans. Two other new species were found only in Patagonia: Cryptococcus frias and Cryptococcus tronadorensis. Three additional new taxa were found, but they are not named as they were only represented by single isolates.

Psychrophilic yeasts from worldwide glacial habitats: diversity, adaptation strategies and biotechnological potential

Glacial habitats (cryosphere) include some of the largest unexplored and extreme biospheres on Earth. These habitats harbor a wide diversity of psychrophilic prokaryotic and eukaryotic microorganisms. These highly specialized microorganisms have developed adaptation strategies to overcome the direct and indirect life-endangering influence of low temperatures. For many years Antarctica has been the geographic area preferred by microbiologists for studying the diversity of psychrophilic microorganisms (including yeasts). However, there have been an increasing number of studies on psychrophilic yeasts sharing the non-Antarctic cryosphere. The present paper provides an overview of the distribution and adaptation strategies of psychrophilic yeasts worldwide. Attention is also focused on their biotechnological potential, especially on their exploitation as a source of cold-active enzymes and for bioremediation purposes.