Microbotryozyma lacustris L. Tian, Y. Y. Zheng, D. Phurbu & Q. M. Wang, 2025

Tian, Lin, Phurbu, Dorji & Zheng, Yan-Yan, 2025, Microbotryozyma lacustris sp. nov. (Basidiomycota, Ustilentylomataceae) and Cyberlindnera basumtsoensis sp. nov. (Ascomycota, Phaffomycetaceae), two novel yeasts isolated from freshwater Lake Basom Tso, China, MycoKeys 126, pp. 135-150 : 135-150

Microbotryozyma lacustris L. Tian, Y. Y. Zheng, D. Phurbu & Q. M. Wang sp. nov.

Fig. 3

Etymology.

The species is named after the lake habitat where the type strain was isolated.

Holotype.

China • Xizang Autonomous Region, Nyingchi City, Gongbo’gyamda County, Basom Lake , from freshwater, GPS: 30°02'11"N, 93°78'53"E, 3440 m a. s. l., on 15 August 2023, Y. Y. Zheng ( holotype CGMCC 2.8854 T permanently preserved in a metabolically inactive state, ex-holotype JCM 10420 = ZYY 1779 ) .

Description.

Culture characteristics: After 3 days of incubation in YM broth at 17 ° C, cells were ellipsoidal to ovoid, measuring 1.9–3.9 × 3.5–6.5 µm, and reproduced by monopolar budding (Fig. 3 ). After one month under the same conditions, prominent rings and sediment were present. On YM agar at 17 ° C for three days, colonies were creamy, smooth, glossy, and exhibited surface ridges with serrated margins. Pseudohyphae were not formed on cornmeal agar. No ascospores or sexual structures were observed on YM, PDA, V 8, or cornmeal agar after six weeks. Ballistoconidia were not produced. Physiological and biochemical characteristics: D-Glucose, sucrose, melibiose, D-arabinose, D-ribose, L-rhamnose, D-mannitol, and raffinose (delayed and weak) were assimilated. The following carbon sources were assimilated weakly or after a delay: D-galactose, sorbose, maltose, cellobiose, trehalose, lactose, melezitose, D-xylose, N-acetyl-D-glucosamine, ethanol, glycerol, galactitol, and hexadecane. Soluble starch, L-arabinose, methanol, erythritol, ribitol, D-glucitol, α-methyl-D-glucoside, DL-lactic acid, succinic acid, citric acid, and inositol were not assimilated. Ammonium sulfate was utilized as a sole nitrogen source; potassium nitrate, sodium nitrite, L-lysine, ethylamine hydrochloride, and cadaverine dihydrochloride were not utilized. Starch-like compounds were not produced. Growth in vitamin-free medium was weak. No growth occurred on 50 % (w / w) glucose – yeast extract agar.

Materials examined.

China • Xizang Autonomous Region, Nyingchi City, Gongbo’gyamda County, Basom Lake , from freshwater, GPS: 29°98'13"N, 93°86'59"E, 3390 m a. s. l., on 21 July 2025, L. Tian, Y. Y. Zheng, D. Phurbu & Q. M. Wang (living culture BSC-W-3-4 , BSC-W-7-4 ) .

Notes.

Strains CGMCC 2.8854 T, BSC-W-3-4 , and BSC-W-7-4 , identified as Microbotryozyma lacustris , cluster within the genus Microbotryozyma but are phylogenetically distinct from their closest relatives, M. collariae and M. swertiae . The D 1 / D 2 domain sequence of strain CGMCC 2.8854 differs by seven substitutions (1.39 %) from that of M. collariae ATCC MYA- 4666 T, while the ITS region shows 44 mismatches (8.78 %, including 29 substitutions and 15 indels), values that exceed thresholds commonly accepted for species delineation in yeasts. Phenotypically, M. lacustris can be clearly distinguished from its congeners by its unique carbon and nitrogen assimilation profile. Specifically, it assimilates melibiose, L-rhamnose, galactitol (delayed), and hexadecane (delayed), all of which are not utilized by M. collariae or M. swertiae . Conversely, it fails to assimilate α-methyl-D-glucoside, potassium nitrate, or ethylamine hydrochloride, compounds that are utilized by both related species. These consistent phenotypic differences, summarized in Table 3, corroborate the phylogenetic data and firmly support its status as a novel species.

Figures

Figure 3. Morphology of M. lacustris sp. nov. (strain CGMCC 2.8854 T). A. Individual colonies by streaking onto Potato Dextrose Agar (PDA) after 3 days; B. Cylindrical arthroconidia on yeast extract – malt extract (YM) after three days of growth at 17 ° C. Scale bars: 10 μm.