Approximately 70% of the isolated yeasts could grow at temperatures above 20°C, and 16% of them were able to grow at ≥30°C. The predominance of psychrotolerant fungi in cold environments has been previously noted, and is attributable to seasonal and local increases in soil temperature due to solar radiation
]. In our study, the temperature measured in situ at the different sampling sites ranged from 0 to 11.9°C, but temperatures up to 20°C have been reported in this region
]. The main obstacle to assessing the yeast communities in Antarctic regions is the scant knowledge regarding their environmental and nutritional requirements. Because the yeast populations/species inhabiting terrestrial and aquatic environments can colonize specific niches, no appropriate method exists for efficiently isolating all species
]. In this work the yeasts were isolated using rich media supplemented with glucose, because almost all known yeasts can assimilate this sugar
]. However, this culture condition could favor the proliferation of yeasts with high metabolic rates, to the detriment of slow-growing yeasts. Nevertheless, large numbers and high species diversity were attained in this study (22 species from 12 genera). Cold-loving yeasts have been isolated mainly from the Antarctic and the Arctic, and from European and South American glaciers
]. In all of these environments, the most ubiquitous species are Rhodotorula laryngis
and Cr. victoriae.
On the other hand, C. sake, D. fristingensis, G. antarctica
and Sp. salmonicolor
have been isolated only in the Southern Cone (South American glaciers and Antarctica). This work reports for the first time the isolation of Cryptococcus gastricus, Cryptococcus gilvescens, D. fristingensis
and Leucosporidiella creatinivora
from an Antarctic region. Also isolated was W. anomalus
, which is not generally found in cold regions.
During molecular analysis of the yeasts, most isolates assigned to the same species possessed identical D1/D2 and ITS sequences. Thus, combining these rDNA regions is a useful technique for rapid identification and typing of yeasts, as others have suggested
]. However, the isolates identified as Leuconeurospora sp.
were 0.7% and 0.9% different in their D1/D2 (578 bp) and ITS (534 bp) sequences, respectively. Similarly, the isolates identified as D. fristingensis
exhibited identical D1/D2 (456 bp) sequences, but their ITS (479 bp) sequences were markedly different (4.4%), and their overlap was punctuated with several gaps. Furthermore, given the physiological differences between isolates that are identical or similar at molecular level, strongly support that the definitions of yeast species must be supplemented by classical characterizations.
Most yeast isolates showed lipase activity, consistent with a previous report in which all of the filamentous fungi from Antarctica displayed this activity
]. Among the “cold loving” yeasts, lipase activity has been described in Pseudozyma antarctica
], Leucosporidium antarcticum
] and in species of Cryptococcus
]. Unlike this last-mentioned study, we detected lipase activity in R. laryngis
also. Lipase activity has also been described in W. anomalus
from tropical environments
]. The least common extracellular activity was xylanase, observed only in the D. fristingensis
isolate. Although this activity has been previously described in Cryptococcus
], no xylanase activity was observed in the Cryptococcus
isolates identified here. Consistent with our results, protease, amylase and esterase extracellular activities have been reported in several yeast species isolated from cold and tropical environments
]. However, we present the first report of extracellular amylase activity in Le. creatinivora
, H. watticus
, Leuconeurospora sp.
and D. fristingensis
. In addition to Mrakia
species, for which extracellular pectinase activity has been described
], we detected pectinase activity in species of Wickerhamomyces, Metschnikowia, Dioszegia, Leucosporidiella
species isolated in this work showed cellulase activity, which has been previously described in Mrakia frigida
isolated from King George Island
]; furthermore, this activity was observed in Cryptococcus
species, contrary to a previous report
]. Extracellular chitinase activity has been reported in Cryptococcus
], but here we observed this activity in M. psychrophila
, Sp. salmonicolor
, Metschnikowia sp.
, Leuconeurospora sp.
and D. fristingensis
. We detected cellulase and chitinase activities in yeasts species that have not been described from cold regions, probably because our sampling sites included areas with vegetation and animal contact and/or were located close to the sea. Cellulose is one of the most abundant carbohydrates produced by plants
] and chitin is the most abundant renewable polymer in the ocean, where it constitutes an important source of carbon and nitrogen
]. Furthermore, significant quantities of lipids exist in phytoplankton
] and in sediments of this region
], which can explain the high incidence of lipase activity found in the yeasts. All of the extracellular enzyme activities analyzed in this work are potentially useful to industry: amylases in food processing, fermentation and pharmaceutical industries; cellulases and pectinases in textiles, biofuel processing and clarification of fruit juice; esterase in the agro-food industries; lipases and proteases in food and beverage processing, detergent formulation and environmental bioremediations; chitinases in biocontrol and treatment of chitinous waste; xylanase as a hydrolysis agent in biofuel and solvent industries