sustainability Review Soil Yeasts in the Vicinity of Syowa Station, East Antarctica: Their Diversity and Extracellular Enzymes, Cold Adaptation Strategies, and Secondary Metabolites Masaharu Tsuji 1,* and Sakae Kudoh 2,3 1 Department of Materials Chemistry, National Institute of Technology, Asahikawa College, Asahikawa 071-8142, Japan 2 Biology Group, National Institute of Polar Research (NIPR), Tachikawa 190-8158, Japan; [email protected] 3 Department of Polar Science, SOKENDAI (The Graduate University for Advanced Studies), Tachikawa 190-8158, Japan * Correspondence: [email protected] or [email protected]; Tel./Fax: +81-(166)-55-8021 Received: 13 May 2020; Accepted: 29 May 2020; Published: 2 June 2020 Abstract: Antarctica is known as one of the harshest environments on Earth, with a frigid and dry climate. Soil yeasts living in such extreme environments can grow by decomposing organic compounds at sub-zero temperatures. Thus far, a list of lichen and non-lichen fungi isolated from the area near Syowa Station, the base of the Japanese Antarctic research expedition, has been compiled and a total of 76 species of fungi have been reported. Yeast, especially basidiomycete yeast, is the dominant fungus in Antarctica. This mini-review summarizes a survey of the yeast diversity in the soil of Eastern Ongul Island and the ability of these yeasts to secrete extracellular enzymes. We also describe the yeast diversity in the soil of the Skarvesnes ice-free region and how these yeasts have adapted to the sub-zero environment. Further, we describe the secondary metabolites of these yeasts, whose production is induced by cold stress. Keywords: Antarctica; cold adaptation; extracellular enzymes; soil yeast diversity 1. Introduction Most of the Earth’s biosphere is a low-temperature region exposed to temperatures below 5 ◦C; this includes the polar regions of Antarctica and the Arctic, the deep sea, and high mountains such as the Himalayas and the Alps. [1]. Antarctica is the southernmost continent on Earth, covering an area of about 14 million km2, making it the fifth-largest continent in the entire world. About 98% of Antarctica is covered in ice and snow, and coastal temperatures are typically between 5 and 35 C[2]. − ◦ Ice- and snow-free areas during the austral summer are distributed along the coast of Antarctica in areas called ice-free regions, where snow and ice melt during the summer months to expose the ground. In Antarctica, most life forms live in these ice-and snow-free areas [3]. Despite being exposed to conditions such as sub-zero temperatures and low availability of nutrients and water, which are detrimental to their survival, fungi living in cold environments can grow at near-zero temperatures. Secretion of extracellular enzymes allows them to utilize complex substances as a source of energy [4]. Therefore, psychrophilic and psychrotolerant fungi play an essential role in the nutrient cycle of polar ecosystems [5,6]. Changes in fungal diversity at polar regions can have a profound effect on local primary production; therefore, understanding the diversity of fungi in polar regions is essential to know the local environment. Sustainability 2020, 12, 4518; doi:10.3390/su12114518 www.mdpi.com/journal/sustainability Sustainability 2020, 12, x FOR PEER REVIEW 2 of 9 Sustainability 2020, 12, 4518 2 of 8 To our knowledge, more than 1000 fungal species from about 400 genera have been identified and documentedTo our knowledge, in Antarctica more than [7]. This 1000 list fungal of species species identified from about by 400culture genera and have collection been identifiedincluded 68%and documentedascomycetes, in23% Antarctica basidiomycetes, [7]. This and list of5% species zygomycetes identified fungi, by culturewith the and last collection 4% consisting included of various68% ascomycetes, other lineages. 23% A basidiomycetes, list of lichenized and and 5% no zygomycetesn-lichenized fungi,fungi isolated with the from last 4%the consistingarea around of Syowavarious Station, other lineages. the base Aof listthe ofJapan lichenized Antarctic and Re non-lichenizedsearch Expedition fungi (JARE), isolated has from been the generated area around and aSyowa total of Station, 76 fungal the basespecies of thehave Japan been Antarctic documented Research [8,9]. Expedition We have investigated (JARE), has the been diversity generated of fungi and a intotal East of 76Ongul fungal Island, species where have the been Syowa documented Station is [8 ,lo9].cated, We have and investigatedthe Skarvesnes the diversityice-free area of fungi that inis aboutEast Ongul 60 km Island, from this where island. the Syowa In Antarctica, Station isyeast, located, especially and the basidiomycete Skarvesnes ice-free yeast, area is the that dominant is about fungus.60 km from Therefore, this island. in this In mini-review, Antarctica, yeast, we summarize especially basidiomycetethe diversity of yeast, yeasts is living the dominant in the soil fungus. near theTherefore, Syowa inStation this mini-review, in Antarctica, we summarizetheir mechanisms the diversity of adaptation of yeasts to living lowin temperatures, the soil near theand Syowa their abilityStation to in Antarctica,secrete extracellular their mechanisms enzymes of at adaptation low temperatures. to low temperatures, We also summarize and their ability the secondary to secrete metabolitesextracellular that enzymes these yeasts at low produce, temperatures. specifically We also under summarize the cold the stress secondary of sub-zero metabolites temperatures. that these yeasts produce, specifically under the cold stress of sub-zero temperatures. 2. Soil Yeast Diversity and Their Ecological Role in East Ongul Island 2. Soil Yeast Diversity and Their Ecological Role in East Ongul Island The Island of East Ongul (69° 1 S, 39° 35 E) is located to the east of Lützow Holm Bay in East AntarcticaThe Island (Figure of 1). East In Ongul1957, Syowa (69◦ 1 Station S, 39◦ 35 was E) established is located to here the as east a base of Lützow for the HolmJARE. BayDuring in East the australAntarctica summer, (Figure East1). InOngul 1957, Island Syowa is Station a snow-and was established ice-free area. here A as total a base of for95 yeast the JARE. strains During were culturedthe austral from summer, soil Eastsamples Ongul from Island East is aOngul snow-and Island ice-free [10]. area. These A totalstrains of 95were yeast classified strains were as basidiomycetescultured from soil belonging samples to from 10 genera East Ongul and 16 Island species [10]. in These six families, strains based were classified on the internal as basidiomycetes transcribed spacerbelonging (ITS) to region 10 genera sequence and 16 speciesand the in D1/D2 six families, domain based sequences on the internal of the 26S transcribed rDNA gene spacer (Table (ITS) 1). region The dominantsequence andyeast the genera D1/D2 in domain East Ongul sequences island of soils the 26Swere rDNA Vishniacozyma gene (Table (29.4%),1). The Naganishia dominant yeast(23.2%), genera and Cystobasidiumin East Ongul island(14.7%). soils At werethe speciesVishniacozyma level, Vishniacozyma(29.4%), Naganishia victoriae(23.2%), (23.2%), and NaganishiaCystobasidium friedmannii(14.7%). (17.9%),At the species Cystobasidium level, Vishniacozyma ongulense (10.5%), victoriae and(23.2%), GlaciozymaNaganishia martinii friedmannii(10.5%) were(17.9%), the mostCystobasidium frequently isolatedongulense yeasts.(10.5%), Our and fungalGlaciozyma survey martinii did not(10.5%) reveal wereany ascomycetous the most frequently yeast from isolated the yeasts.soil of East Our Ongul fungal Islandsurvey [10]. did not reveal any ascomycetous yeast from the soil of East Ongul Island [10]. FigureFigure 1. 1. MapMap of of Antarctica Antarctica and and the the locations locations of of Sy Syowaowa Station Station and the Skarvsnes ice-free area area.. The left side of the map shows the Antarctic continent, and the right side shows the area near The left side of the map shows the Antarctic continent, and the right side shows the area near Syowa Station. Syowa Station. Of these 16 yeast species, it was initially reported that Cystobasidium lysinophilum, Goffeauzyma Of these 16 yeast species, it was initially reported that Cystobasidium lysinophilum, Goffeauzyma gilvescens, Holtermanniella wattica, Mrakia gelida, Naganishia albidosimilis, Udeniomyces puniceus, and gilvescens, Holtermanniella wattica, Mrakia gelida, Naganishia albidosimilis, Udeniomyces puniceus, and Vishniacozyma carnescens could not be grown in vitamin-free medium [11–14]. However, in our previous Vishniacozyma carnescens could not be grown in vitamin-free medium [11–14]. However, in our study, all species grew in vitamin-free medium and at sub-zero temperatures. The measured total previous study, all species grew in vitamin-free medium and at sub-zero temperatures. The carbon and nitrogen concentrations in the soil samples from 226 points in East Ongul Island were measured total carbon and nitrogen concentrations in the soil samples from 226 points in East Ongul 0.063% 0.087% and 0.0025% 0.0023%, respectively. Based on this result, the soil on the island Island were± 0.063% ± 0.087% and± 0.0025% ± 0.0023%, respectively. Based on this result, the soil on the Sustainability 2020, 12, 4518 3 of 8 is an extreme oligotrophic environment [15]. Therefore, it is thought that the yeasts living on this island have acquired unusual vitamin-free growth characteristics to survive the cold and extremely oligotrophic environment