Absidia koreana H.B. Lee, H.W. Lee&T.T.T. Nguyen, sp. nov.
MycoBank number: MB 813805; Faces of fungi number: FoF 01015; Fig. 1
Etymology: koreana. Referring to the country which from the species was first isolated (Korea, Dokdo island).
Holotype: CNUFC-EML-IFS45-1, deposited at the Environmental Microbiology Laboratory Herbarium, Chonnam National University, Gwangju, Korea.
Colony exhibits rapid growth onSMA, attaining a diameter of 62 – 65 mm after 4 days at 25 °C. The initial color of the colonies is white, which later changed to grayish white or smoky gray, and the colonies cover almost the entire surface of the agar in the petri dishes within 5 days. The colony reverse is white and irregularly zonate. Although the mycelial growth on SMA is sparse, the sporulation is excellent. Sporangia 19.33 – 23.64 μm × 21.06 – 26.35 μm in diam., and are globose to slightly elliptical, having sporangial net wall. Sporangiophores are 3.84 – 4.60 μm wide and arise as 1 – 6 sporangiophores (average 2 – 4) per whorl from a single point in the stolons. They show occasional branching, with the presence of a septum approximately 17.71 – 23.53 μm in length below the apophysis. Collar appears around the base of each columella. Sporangiospores are short – cylindrical or cylindrical, and measure 2.15 – 2.35 μm wide × 3.54 – 4.48 long. Columellae are 10.90 – 16.96 μm × 11.46 – 18.89 μm diam., and typically globose with a collarette. Zygospores are not observed in this medium. Colonies exhibit slower growth on PDA than on SMA, attaining 39.5 – 41 mm in diam. after 4 days at 25 °C, which is about 15 mm higher than that attained in 3 days. The colonies exhibit slower growth on PDA than on SMA, attaining 39.5–41 mm in diam., and 1.5 mm in height after 4 days at 25 °C. At 25 °C, the colonies appear dark brown in the center, with a lighter margin. The colony reverse is white, with the wavy zonation much more pronounced than that shown by colonies grown on the SMA medium. Sporangiophores are 3.69 – 4.68 μm wide, erect, and arise as a single sporangiophore or in groups of 2 – 3 from the same location on the stolon. They exhibit occasional branching with a septum consistently present 14.38– 19.80 μm below the apophysis. Sporangia measure 18.78 – 27.59 μm × 19.80 – 29.57 μm in diam., and are globose to slightly elliptical. Sporangiospores measure 1.73 – 1.98 μm wide × 2.07 – 4.28 μm long, and are cylindrical. Columellae measure 10.64 – 12.98 μm × 15.60 – 16.83 μm, and appear globose, with a small collarette. Chlamydospores and vesiculate sporangiophores were observed at 32 °C.
On SDA, Colonies grow more rapidly than on SMA and PDA, attaining 73 – 75 mm in diam. after 4 days at 25 °C. The initial color of the colonies at 25 °C is grayish white, which later changed to grayish brown. The colony reverse is grayish white, with wavy zonation. Sporangiophores are 2.17 – 4.28 μm wide, erect, and arise either singly or in groups of 2 – 4 sporangiophores from the same location on the stolen. They exhibit occasional branching, and always have a septum under the sporangium. Sporangia measure 24.97 – 42.21 μm × 23.24 – 35.94 μm in diam., and are globose to slightly elliptical in appearance. Sporangiospores are cylindrical and measure 2.0 –2.57 μm wide × 3.25 – 4.15 μm long. No chlamydospores or zygospores are detected in this medium. Although the SDA medium exhibit good mycelial growth, a small number of sporangia are produced. A temperature from 27 °C to 32 °C is found to be optimal for the growth of Absidia, as shown in the colonies observed on PDA, SMA, and SDA. The fungus shows restricted growth at 37 °C.
Material examined: REPUBLIC OF KOREA, Division of Food Technology, Biotechnology & Agrochemistry, College of Agriculture & Life Sciences, Chonnam National University, Gwangju 61186, Korea, from soil in Dokdo island in the East Sea of Korea; KOSPFGC 1143 (ex-type) at Culture Collection of National Institute of Biological Resources (NIBR), Incheon, Korea, and isotype EML-IFS45-2 preserved as glycerol stock at −80 °C in the CNUFC.
The isolate was observed to grow over a wide range of temperatures with varying growth rates on PDA, SMA, and SDA. The average growth rates of EML-IFS45-1 on PDA, SMA, and SDA were 13 mm, 21 mm, and 27 mm per day, respectively. Optimal growth was observed at 27 °C, slow growth was observed at 18 °C, and extremely slow growth at 37 °C (Fig. 2).
Fig. 1 Morphology of Absidia koreana (EML-IFS45-1, holotype). a colony in synthetic mucor agar. b simple sporangiophore with young sporangium. c mature sporangia with sporangial net wall and sporangiospores. d attachment of sporangiophores. e columella with collarette and septum (yellow arrow). f sporangiospores. Scale bars: b, c, f = 10 μm, d = 50 μm, e = 20 μm.
Fig. 2 Maximum likelihood phylogenetic tree inferred from the combined dataset of 18S rDNA, 28S rDNA, elongation factor (EF-1α), and actin (Actin-1) gene sequences from Gongronella koreana sp. nov. EML-TS2Bp and EML-TS2Bp-1 and related species. Sequences of Umbelopsis nana and U. isabellina were used as outgroups. Numbers at the nodes indicate the bootstrap values (>50 %) from 1000 replications. The bar indicates the number of substitutions per position.