Psychromyces glacialis (’lis. L. masc. adj. glacialis icy, frozen).

MycoBank number: MB 834190; Index Fungorum number: IF 834190; Facesoffungi number: FoF;

Streak cultures at 15 °C after 14 days on PDA agar mucoid, orange white (5A2), filamentous, 2–6 mm diameter, margin composed of fine filaments immersed into the medium (Fig. 5a). Synnemata-like dense bundles of hyphae form on initial inoculation points (Fig. 5c). Yeast colonies (Fig. 5b) visible after 3 weeks, attain 2 mm diameter after 7 weeks on PDA and MEA, 0.5 mm on SNA, pastel red (7A4), convex and mat. After 3 months on PDA at 15 °C, the filamentous colonies reach up to 40 mm diameter, become pale red to pastel red (7A3, 8B4), mat. Mycelium in some strains without clamps (EXF-13111), 1.5–2.0 µm wide (Fig. 5d), or with clamps (Fig. S6), 2–4 µm wide, branched (Fig. S6 d–j). After 14 days of incubation, numerous teliospores are produced intercalary (Figs 5d–g and S6 h, j–l). Teliospores oblong, (5.5–) 8×10 (–13) (mean; min-max: 5.5–13) µm. Budding occurring in yeast colonies polar or occasionally multilateral, sessile or on short or long denticles, and with sympodial proliferation. Individual yeast cells on MEA: 8.5±2 (mean±SD; min-max: 5.5–11)×(2.5) 3.5±0.5 (4.5) µm, on PDA: 7.5±3 (mean±SD; min-max: 5–12)×3.5±0.5 (mean±SD; min-max: 3–4) µm. Dalmau plate culture on CMA agar, 7 weeks of incubation: numerous teliospores on densely septated mycelium.

Assimilated compounds: α-d-glucose, sucrose, raffinose, trehalose, maltose, melezitose, cellobiose (sometimes weak), nitrate, nitrite and cadaverine. Variable: salicin, l-sorbose, d-xylose, l-arabinose, d-glucosamine and l-lysine. Not assimilated compounds: melibiose, d-galactose, starch, d-arabinose, d-ribose and glycerol. Additional data on C source assimilation obtained by Biology YT plates only are given in Table S2. Does not grow in the presence of 10%, 15% NaCl, 50% glucose. Growth at 5, 10, 15 °C is positive; no growth evident at 20 °C. Fermentation abilities absent.

The holotype, CBS 16467, originated from subglacial ice of Vestre Brøggerbreen glacier (78° 54′ 55″ N 11° 45′ 48″ E) in Norway, Svalbard, in July 2017 by Laura Perini. It is permanently preserved in a metabolically inactive state at the CBS Yeast Collection of the Westerdijk Fungal Biodiversity Institute, Utrecht, the Netherlands. The ex-type strain has been deposited in the Ex Culture Collection of the Infrastructural Centre Mycosmo (MRIC UL), Slovenia (www.ex-genebank. com) at the Department of Biology, Biotechnical Faculty, University of Ljubljana, Slovenia, as strain EXF-13111. Accession numbers of DNA sequences derived from type: MT301949 (LSU rDNA), MK671633 (ITS), MT248408 (SSU), MT260392 (CYTB), MT260389 (TEF), MW036268 (RPB2).

Other examined strains: Greenland, Greenland Ice Sheet, 60 km east of Kangerlussuaq, 67° 04′ 43″ N 49° 20′ 29″ W, isolated from dark ice (EXF-12419), isolated from cryoconite (EXF-12886, EXF-12454), July 2017, L. Perini; Norway, Svalbard, Midtre Lovénbreen glacier, isolated from subglacial ice (EXF-12984), SV, Vestre Brøggerbreen glacier, isolated from subglacial ice (EXF-12991), August 2017, L. Perini.

Fig. 5. Morphology of Psychromyces glacialis. (a, b) cultures of Psychromyces glacialis EXF-13111 at 15 °C: (a) PDA, dimorphic culture after 3 weeks of incubation, (b) PDA, yeast culture grown from single yeast colony after 1 month of incubation, (c) PDA, filamentous culture grown from the margin of filamentous colony after 1 month of incubation; (d–g) teliospores grown on (d) CMA, Dalmau plate after 1 month of incubation in 60% lactic acid, (e) PDA, margin of filamentous colony after 10 weeks of incubation in 60% lactic acid, (f) PDA, yeast part of colony after 3 weeks of incubation, mounted in water, (g) PDA, filamentous colony after 3 weeks, coloured with calcofluor white; (h–n) yeast cells, (h, i, m, n) PDA, from dimorphic culture after 3 weeks of incubation, (h–i) mounted in water, (m–n) stained with calcofluor white (l) PDA, dimorphic culture in water after 1 month of growth on PDA, rudimentary pseudohyphae; (i–m) PDA, budding cells on short or long denticles, (n) PDA, yeast cells with inclusions.