Chemical characterization and biological effect of exopolysaccharides synthesized by Antarctic yeasts Cystobasidium ongulense AL101 and Leucosporidium yakuticum AL102 on murine innate immune cells

The current study aimed to investigate exopolysaccharides (EPSs) produced by two Antarctic yeasts isolated from soil and penguin feathers samples collected on Livingston Island (Antarctica). The strains were identified as belonging to the species Leucosporidium yakuticum (LY) and Cystobasidium ongulense (CO) based on molecular genetic analysis. The EPS production was investigated using submerged cultivation. Different chemical, chromatographic, and spectral analyses were employed to characterize EPSs. LY accumulated 5.5 g/L biomass and 4.0 g/L EPS after 120 h of cultivation, while CO synthesized 2.1 g/L EPS at the end of cultivation, and the biomass amount reached 5.5 g/L. LY-EPS was characterized by a higher total carbohydrate content (80%) and a lower protein content (18%) by comparison with CO-EPS (62%, 30%). The LY-EPS mainly consisted of mannose (90 mol%), whereas CO-EPS had also glucose, galactose, and small amounts of uronic acids (8-5 mol%). Spectral analyses (FT-IR and 1D, 2D NMR) revealed that LY-EPS comprised a typical β-(1 → 4)-mannan. Branched (hetero)mannan, together with β/α-glucans constituted the majority of CO-EPS. Unlike LY-EPS, which had a high percentage of high molecular weight populations, CO-EPS displayed a large quantity of lower molecular weight fractions and a higher degree of heterogeneity. LY-EPS (100 ng/mL) elevated significantly interferon gamma (IFN-γ) production in splenic murine macrophages and natural killer (NK) cells. The results indicated that newly identified EPSs might affect IFN-γ signaling and in turn, might enhance anti-infectious responses. The data obtained also revealed the potential of EPSs and yeasts for practical application in biochemical engineering and biotechnology.

Response to Cold: A Comparative Transcriptomic Analysis in Eight Cold-Adapted Yeasts

Microorganisms have evolved to colonize all biospheres, including extremely cold environments, facing several stressor conditions, mainly low/freezing temperatures. In general, terms, the strategies developed by cold-adapted microorganisms include the synthesis of cryoprotectant and stress-protectant molecules, cold-active proteins, especially enzymes, and membrane fluidity regulation. The strategy could differ among microorganisms and concerns the characteristics of the cold environment of the microorganism, such as seasonal temperature changes. Microorganisms can develop strategies to grow efficiently at low temperatures or tolerate them and grow under favorable conditions. These differences can be found among the same kind of microorganisms and from the same cold habitat. In this work, eight cold-adapted yeasts isolated from King George Island, subAntarctic region, which differ in their growth properties, were studied about their response to low temperatures at the transcriptomic level. Sixteen ORFeomes were assembled and used for gene prediction and functional annotation, determination of gene expression changes, protein flexibilities of translated genes, and codon usage bias. Putative genes related to the response to all main kinds of stress were found. The total number of differentially expressed genes was related to the temperature variation that each yeast faced. The findings from multiple comparative analyses among yeasts based on gene expression changes and protein flexibility by cellular functions and codon usage bias raise significant differences in response to cold among the studied Antarctic yeasts. The way a yeast responds to temperature change appears to be more related to its optimal temperature for growth (OTG) than growth velocity. Yeasts with higher OTG prepare to downregulate their metabolism to enter the dormancy stage. In comparison, yeasts with lower OTG perform minor adjustments to make their metabolism adequate and maintain their growth at lower temperatures.

Fungal diversity in the coastal waters of King George Island (maritime Antarctica)

Fungi have been reported as common inhabitants of the maritime waters in Antarctica by studies based on culture-dependent methods. More recently, results obtained using DNA sequencing technologies, revealed that fungal diversity worldwide has been underestimated by culture methods. The present study provides the first characterization of fungal communities in the coastal waters of King George Island (maritime Antarctica) using both culture-dependent and high-throughput sequencing (HTS) methods. HTS demostrated a higher level of fungal diversity than the obtained by culture methods. A high prevalence of basidiomycetous yeasts and ascomycetous filamentous fungi was confirmed by both methods, however, Chythriomycota, Rozellomycota, lichenized fungi and Malassezia spp. were detected only by HTS. Correspondingly, members of some genera, such as Metschnikowia, were only found by culture-dependent methods. Our results confirm that culturing and HTS, should be seen as complementary approaches that enable one to obtain a more comprehensive picture of the composition of microbial communities.

Identification of Stress-Related Genes and a Comparative Analysis of the Amino Acid Compositions of Translated Coding Sequences Based on Draft Genome Sequences of Antarctic Yeasts

Microorganisms inhabiting cold environments have evolved strategies to tolerate and thrive in those extreme conditions, mainly the low temperature that slow down reaction rates. Among described molecular and metabolic adaptations to enable functioning in the cold, there is the synthesis of cold-active proteins/enzymes. In bacterial cold-active proteins, reduced proline content and highly flexible and larger catalytic active sites than mesophylls counterparts have been described. However, beyond the low temperature, microorganisms' physiological requirements may differ according to their growth velocities, influencing their global protein compositions. This hypothesis was tested in this work using eight cold-adapted yeasts isolated from Antarctica, for which their growth parameters were measured and their draft genomes determined and bioinformatically analyzed. The optimal temperature for yeasts' growth ranged from 10 to 22°C, and yeasts having similar or same optimal temperature for growth displayed significative different growth rates. The sizes of the draft genomes ranged from 10.7 (Tetracladium sp.) to 30.7 Mb (Leucosporidium creatinivorum), and the GC contents from 37 (Candida sake) to 60% (L. creatinivorum). Putative genes related to various kinds of stress were identified and were especially numerous for oxidative and cold stress responses. The putative proteins were classified according to predicted cellular function and subcellular localization. The amino acid composition was compared among yeasts considering their optimal temperature for growth and growth rates. In several groups of predicted proteins, correlations were observed between their contents of flexible amino acids and both the yeasts' optimal temperatures for growth and their growth rates. In general, the contents of flexible amino acids were higher in yeasts growing more rapidly as their optimal temperature for growth was lower. The contents of flexible amino acids became lower among yeasts with higher optimal temperatures for growth as their growth rates increased.

Characterization of gelatinase produced by Antarctic Mrakia sp

In the present study, 20 psychrotolerant yeast species isolated from the soils of King George Island in the sub-Antarctic region were evaluated for the production of extracellular gelatinase, an enzyme with high potential for applications in diverse areas, such as food and medicine. The production of extracellular gelatinase was confirmed in the yeasts Metschnikowia sp., Leucosporidium fragarium, and Mrakia sp., the last one being the yeast in which the highest gelatinase activity was detected. The enzyme was purified from cultures of Mrakia sp., and the effect of different physical-chemical factors on its activity was determined. The gelatinase produced by Mrakia sp. would correspond to a protein of relative molecular weight (rMW) 37,000, which displayed the highest activity at 36°C, pH 7.0, 10 mM CaCl ₂ , and 5 mM ZnSO ₄ .

Antarctic yeasts: analysis of their freeze-thaw tolerance and production of antifreeze proteins, fatty acids and ergosterol

BACKGROUND

Microorganisms have evolved a number of mechanisms to thrive in cold environments, including the production of antifreeze proteins, high levels of polyunsaturated fatty acids, and ergosterol. In this work, several yeast species isolated from Antarctica were analyzed with respect to their freeze-thaw tolerance and production of the three abovementioned compounds, which may also have economic importance.

RESULTS

The freeze-thaw tolerance of yeasts was widely variable among species, and a clear correlation with the production of any of the abovementioned compounds was not observed. Antifreeze proteins that were partially purified from Goffeauzyma gastrica maintained their antifreeze activities after several freeze-thaw cycles. A relatively high volumetric production of ergosterol was observed in the yeasts Vishniacozyma victoriae, G. gastrica and Leucosporidium creatinivorum, i.e., 19, 19 and 16 mg l- 1, respectively. In addition, a high percentage of linoleic acid with respect to total fatty acids was observed in V. victoriae (10%), Wickerhamomyces anomalus (12%) and G. gastrica (13%), and a high percentage of alpha linoleic acid was observed in L. creatinivorum (3.3%).

CONCLUSIONS

Given these results, the abovementioned yeasts are good candidates to be evaluated for use in the production of antifreeze proteins, fatty acids, and ergosterol at the industrial scale.