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

Abstract

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.

Keywords: Antarctica; Biotechnology; Enzymes; Freshwater; Fungi.

Fig. 1

Satellite images showing the locations of King George Island and Deception Island in the South Shetland Island archipelago, maritime Antarctica, and photographs of the two lakes sampled in the current study. a Antarctic Continent with Antarctic Peninsula highlighted by red rectangle, b Antarctic Peninsula with King George Island (KGI) and Deception Island (DI) highlighted by red rectangle, c coastal supralittoral Hennequin Lake, Hennequin Point on King George Island and d Kroner Lake on Deception Island. Source: Google Earth Pro, 2019 (a and b) and Luiz H. Rosa (c and d)

Fig. 2

Mao Tao rarefaction curves, with 95% confidence limits, of fungal communities isolated from samples of a cotton baits and b biofilm from Antarctic lakes; blue lines indicate 95% confidence limits

Fig. 3

Venn diagram illustrating the similarities in fungal community composition obtained from cotton baits and biofilm samples from Antarctic lakes

Fig. 4

Enzymes detected with higher and lower frequency amongst all isolates. Protease and lipase were the most frequently observed, while cellulase and pectinase were the least frequent