Yeast Activities Involved in Carbon and Nitrogen Cycles in Antarctica

Characteristics of a novel heterotrophic nitrification-aerobic denitrification yeast, Barnettozyma californica K1

Yeast strain K1, isolated from surface sediment, was identified as Barnettozyma californica. The strain showed efficient heterotrophic nitrification and aerobic denitrification (HN-AD) at initial ammonium, nitrite and nitrate concentrations of 14-140 mg/L. Additionally, the optimum carbon source for its growth and nitrogen removal activity was sucrose, followed by glucose, acetate and citrate. The maximum removal efficiencies of ammonium, nitrite and nitrate were 99.11%, 99.13% and 98.84% under 48 h of culture with sucrose at 140 mg/L nitrogen and the corresponding removal efficiencies of total nitrogen were 90.16%, 86.65% and 81.48%, respectively. The optimum conditions for the inorganic nitrogen removal and growth of strain K1 were a C/N of 18 and a salinity of 5-15 ppt. The amoA, nirK and nosZ genes of K1 were detected. All the results suggest that B. californica K1 is capable of HN-AD and has the potential to remove inorganic nitrogen from wastewater.

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.

Metabolic activity and bioweathering properties of yeasts isolated from different supraglacial environments of Antarctica and Himalaya

Yeasts have been frequently isolated from cold habitats, but their contribution to essential ecological processes such as the mineralization of organic matter in these environments is less known. Here, the diversity, metabolic capability, and extracellular enzyme profiles of yeasts from snow, blue ice and cryoconite hole environments from East Antarctica and cryoconite holes from a glacier in Western Himalaya were determined. Eighty-six yeast strains isolated were affiliated to the genera Glaciozyma, Goffeauzyma, Mrakia, Phenoliferia, and Rhodotorula. Variations in the abundance, diversity, physiological properties, extracellular enzyme and carbon substrate utilization patterns of the isolated yeasts, reflect the specific environmental conditions from which they were isolated. Overall, 20-90% of the yeasts across all habitat types and geographical locations produced extracellular enzymes to degrade proteins, esters, carbohydrates, pectin, cellulose, lignin, and tannin. About 10 and 29% of the yeasts also exhibited ability to solubilize rock-minerals like phosphate and silicate, respectively. Additionally, selected isolates were able to metabolize 28-93% of the carbon substrates comprising different compound classes on Biolog YT plates. Overall, the ability of yeasts to use diverse organic compounds prevalent on the glacier surface, points to their ecological significance in the decomposition of organic matter, cycling of nutrients, and in the weathering of minerals in supraglacial environments. Moreover, their wide metabolic capabilities suggest that they can colonize new niches and environments when meltwater export during the summer that enables links with surrounding ecosystems.

Effects of Sea Animal Activities on Tundra Soil Denitrification and nirS- and nirK-Encoding Denitrifier Community in Maritime Antarctica

In maritime Antarctica, sea animals, such as penguins or seals, provide a large amount of external nitrogen input into tundra soils, which greatly impact nitrogen cycle in tundra ecosystems. Denitrification, which is closely related with the denitrifiers, is a key step in nitrogen cycle. However, effects of sea animal activities on tundra soil denitrification and denitrifier community structures still have received little attention. Here, the abundance, activity, and diversity of nirS- and nirK-encoding denitrifiers were investigated in penguin and seal colonies, and animal-lacking tundra in maritime Antarctica. Sea animal activities increased the abundances of nirS and nirK genes, and the abundances of nirS genes were significantly higher than those of nirK genes (p < 0.05) in all tundra soils. Soil denitrification rates were significantly higher (p < 0.05) in animal colonies than in animal-lacking tundra, and they were significantly positively correlated (p < 0.05) with nirS gene abundances instead of nirK gene abundances, indicating that nirS-encoding denitrifiers dominated the denitrification in tundra soils. The diversity of nirS-encoding denitrifiers was higher in animal colonies than in animal-lacking tundra, but the diversity of nirK-encoding denitrifiers was lower. Both the compositions of nirS- and nirK-encoding denitrifiers were similar in penguin or seal colony soils. Canonical correspondence analysis indicated that the community structures of nirS- and nirK-encoding denitrifiers were closely related to tundra soil biogeochemical processes associated with penguin or seal activities: the supply of nitrate and ammonium from penguin guano or seal excreta, and low C:N ratios. In addition, the animal activity-induced vegetation presence or absence had an important effect on tundra soil denitrifier activities and nirK-encoding denitrifier diversities. This study significantly enhanced our understanding of the compositions and dynamics of denitrifier community in tundra ecosystems of maritime Antarctica.