Savitreea siamensis sp. nov., an ascomycetous yeast species in the family Saccharomycetaceae discovered in Thailand.

Four yeast strains, representing a novel anamorphic species, were isolated in Thailand. The two strains (ST-3660T and ST-3647) were obtained from two different estuarine water samples in a mangrove forest. Strain DMKU-FW1-37 was derived from a grease sample, and another strain (TSU57) was isolated from a fruiting body of Phallus sp. Pairwise sequence analysis showed that the four strains had identical or differed by only one nucleotide substitution in the D1/D2 domains of the large subunit (LSU) rRNA gene, and differed by one to three nucleotide substitutions in the internal transcribed spacer (ITS) regions. Savitreea pentosicarens is the most closely related species to the four strains, but with 9-10 (1.57-1.72 %) nucleotide substitutions in the D1/D2 domains of the LSU rRNA gene and 29-31 (4.22-4.45 %) nucleotide substitutions in the ITS regions. Phylogenetic analyses based on the concatenated sequences of the ITS regions and the D1/D2 domains of the LSU rRNA gene showed that the four strains form a well-separated lineage from S. pentosicarens with high bootstrap support, confirming that they represent a distinct species. Therefore, the four strains are assigned as representives of a novel species of the genus Savitreea, for which the name Savitreea siamensis sp. nov. is proposed. The holotype is TBRC 4481T and the ex-type is PYCC 9794T (=ST-3660T). The MycoBank number of the novel species is MB 851951.

Evaluation of thermotolerant and ethanol-tolerant Saccharomyces cerevisiae as an alternative strain for bioethanol production from industrial feedstocks.

Despite the fact that yeast Saccharomyces cerevisiae is by far the most commonly used in ethanol fermentation, few have been reported to be resistant to high ethanol concentrations at high temperatures. Hence, in this study, 150 S. cerevisiae strains from the Thailand Bioresource Research Center (TBRC) were screened for ethanol production based on their glucose utilization capability at high temperatures. Four strains, TBRC 12149, 12150, 12151, and 12153, exhibited the most outstanding ethanol production at high temperatures in shaking-flask culture. Among these, strain TBRC 12151 demonstrated a high ethanol tolerance of up to 12% at 40 °C. Compared to industrial and laboratory strains, TBRC 12149 displayed strong sucrose fermentation capacity whereas TBRC 12153 and 12151, respectively, showed the greatest ethanol production from molasses and cassava starch hydrolysate at high temperatures in shaking-flask conditions. In 5-L batch fermentation, similarly to both industrial strains, strain TBRC 12153 yielded an ethanol concentration of 66.5 g L-1 (58.4% theoretical yield) from molasses after 72 h at 40 °C. In contrast, strain TBRC12151 outperformed other industrial strains in cell growth and ethanol production from cassava starch hydrolysis at 40 °C with an ethanol production of 65 g L-1 (77.7% theoretical yield) after 72 h. Thus, the thermotolerant and ethanol-tolerant S. cerevisiae TBRC 12151 displayed great potential and possible uses as an alternative strain for industrial ethanol fermentation using cassava starch hydrolysate. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-022-03436-4.

Exploration of yeast communities in fresh coconut, palmyra, and nipa palm saps and ethanol-fermenting ability of isolated yeasts.

This study aimed to explore communities and the ethanol-fermenting ability of yeasts in fresh coconut, palmyra, and nipa palm saps. From the 90 samples of coconut, palmyra, and nipa palm saps, 204 yeast isolates were isolated and identified as 15 species in the phylum Ascomycota and a species (one strain) in Basidiomycota. Saccharomyces cerevisiae, Hanseniaspora guilliermondii, and Lachancea thermotolerans were found in the saps of all three palm species. Candida tropicalis and Pichia kudriavzevii were obtained from the coconut and palmyra palm saps, Hanseniaspora vineae, Lachancea fermentati, and Pichia manshurica were present in the coconut and nipa palm saps, whereas Torulaspora delbrueckii was found in the palmyra and nipa palm saps. The species with the highest occurrence in the saps of coconut, palmyra, and nipa palms was S. cerevisiae with 76.67%, 86.70%, and 100% frequency of occurrence, respectively. Using principal coordinates analysis for ordination, no marked difference was observed in the yeast communities from the saps of the three palm species. A total of 199 isolates were found to possess ethanol-fermentation ability when cultivated using shake flask in 160 g/L of glucose medium at 28°C for 48 h. Lachancea fermentati YSP-383, isolated from nipa palm sap, produced the highest amount of ethanol (76.74 g/L). Twenty-six isolates of Candida sanyaensis (1), C. tropicalis (1), H. guilliermondii (7), L. fermentati (8), L. thermotolerans (1), Pichia kudriavzevii (2), and S. cerevisiae (6) produced high amounts of ethanol ranging from 69.57 to 76.74 g/L. The result demonstrated that yeasts in the palm saps could play roles in the natural fermentation of palm saps.

Yeast Associated with Rice Phylloplane and Their Contribution to Control of Rice Sheath Blight Disease.

The phylloplane is an important habitat for yeasts and these yeasts may have antagonistic activities against pathogens and could be used as biocontrol agents. To investigate rice phylloplane yeasts, 282 strains were isolated from 89 rice leaf samples and identified as 15 known yeast species in the phylum Ascomycota and 35 known and two potential new species in the phylum Basidiomycota. The majority of rice phylloplane yeasts belonged to the phylum Basidiomycota. The evaluation of antagonistic activities of 83 yeast strains against rice pathogenic fungi Pyricularia oryzae, Rhizoctonia solani, Fusarium moniliforme, Helminthosporium oryzae and Curvularia lunata revealed that 14 strains inhibited these pathogens. Among the antagonistic strains, Torulaspora indica DMKU-RP31, T. indica DMKU-RP35 and Wickerhamomyces anomalus DMKU-RP25 inhibited all rice pathogens tested, and the production of volatile organic compounds, fungal cell wall degrading enzymes and biofilm were the possible antagonistic mechanisms against all rice pathogens tested in vitro. These yeast strains were evaluated for controlling rice sheath blight caused by R. solani in rice plants in the greenhouse and were found to suppress the disease by 60.0-70.3%, whereas 3% validamycin suppressed by 83.8%. Therefore, they have potential for being developed to be used as biocontrol agents for rice sheath blight.

Torulaspora nypae sp. nov., a novel yeast species isolated from nipa (Nypa fruticans Wurmb.) inflorescence sap in southern Thailand.

Two strains (YSP-384 and YSP-399), representing a novel Torulaspora species, were isolated from two nipa inflorescence sap samples collected in Trang province in the southern part of Thailand. The two strains had identical sequences of the D1/D2 domains of the large subunit (LSU) rRNA gene and the internal transcribed spacer (ITS) regions. The two strains were closest to Torulaspora maleeae CBS 10694T, but with 1.1 % nucleotide substitutions in the D1/D2 domains of the LSU rRNA gene and 5.2 % nucleotide substitutions in the ITS regions. Phylogenetic analysis based on the concatenated sequences of the ITS regions and the D1/D2 domains of the LSU rRNA gene supported that the two strains represented a distinct species in the genus Torulaspora. Some phenotypic characteristics of the two strains differed from T. maleeae including the two strains have ability to assimilate d-xylose, d-glucono-δ-lactone and melizitose, and inability to ferment maltose and raffinose, whereas T. maleeae has opposite results. Therefore, the two strains are described as representing a novel species, for which the name Torulaspora nypae sp. nov. was proposed.

Candida xylosifermentans sp. nov., a d-xylose-fermenting yeast species isolated in Thailand.

Three strains, representing a novel anamorphic and d-xylose-fermenting yeast species, were isolated from moss (ST-302T), seawater (ST-1169) and peat (DMKU-XE12) collected from the southern part of Thailand. The three strains had identical sequences of the D1/D2 regions of the large subunit (LSU) rRNA gene and the internal transcribed spacer (ITS) regions. Candida flosculorum CBS 10566T and Candida sharkiensis CBS 11368T were the most closely related species with 7.9 % nucleotide substitutions in the D1/D2 regions of the LSU rRNA gene, and 10.3 and 12.6% nucleotide substitutions in the ITS regions, respectively. Phylogenetic analysis based on the concatenated sequences of the ITS and the D1/D2 regions confirmed that the three strains represented a distinct anamorphic species in the Clavispora clade. Therefore, the three strains were described as a novel species, for which we propose the name Candida xylosifermentans sp. nov.

Hannaella siamensis sp. nov. and Hannaella phetchabunensis sp. nov., two new anamorphic basidiomycetous yeast species isolated from plants.

Eight strains, representing two novel anamorphic yeast species, consisted of five strains isolated from the external surfaces of rice leaves (DMKU-RP72(T), DMKU-RP109, DMKU-RP119, YE-124 and YE-156) and one from a corn leaf (DMKU-CP430(T))4 collected in Thailand, and one strain isolated from each of a composite flower (11-1114) and a fallen dead leaf (12-301); the latter two were collected in Belize. On the basis of sequence analysis of the D1/D2 region of the large subunit rRNA gene and the internal transcribed spacer (ITS) region, they were suggested to be two novel species of the genus Hannaella. Seven strains (DMKU-RP72(T), DMKU-RP109, DMKU-RP119, YE-124, YE-156, 11-1114 and 12-301) differed from each other by 0-3 nt substitutions in the D1/D2 region and by 0-1 nt substitutions in the ITS region. In terms of pairwise sequence similarities of the D1/D2 region these seven strains were closest to Hannaella zeae, but with 1.2-1.7% (7-9) nucleotide substitutions. The sequences of the ITS region of these seven strains differed from H. zeae by 3.7-3.9% (16-17) nucleotide substitutions. Therefore, they were assigned to a single novel species and the name Hannaella siamensis sp. nov. has been proposed. The type strain is DMKU-RP72(T) ( = BCC 69493(T) = NBRC 110425(T) = CBS 13533(T)). Strain DMKU-CP430(T) represents the second novel species and was also most closely related to H. zeae, but with 1.0% (6) nucleotide substitutions in the D1/D2 region and 3.2% (14) nucleotide substitutions in the ITS region. It was assigned to the proposed novel species, Hannaella phetchabunensis sp. nov. (type strain DMKU-CP430(T) = BCC 69492(T) = NBRC 110424(T) = CBS 13386(T)).

Yamadazyma insecticola f.a., sp. nov. and Yamadazyma epiphylla f.a., sp. nov., two novel yeast species.

Two yeast strains representing two novel yeast species were isolated from frass of an unidentified insect (ST-78(T)) and the external surfaces of rice leaves (YE170(T)) collected in Thailand. The two strains were genetically, morphologically and phenotypically distinct from recognized species and were found to represent two novel species of the genus Yamadazyma although formation of ascospores was not observed. In terms of pairwise sequence similarity of the D1/D2 region of the large subunit rRNA gene, the closest relative of strain ST-78(T) was Candida lessepsii CBS 9941(T) but with 3.8% nucleotide substitutions, while the closest relative of strain YE170(T) was strain ST-78(T) but with 4.3% nucleotide substitutions. Analysis of the sequences of the internal transcribed spacer 1 and 2 (ITS1-2) regions revealed that strain ST-78 differed from C. lessepsii CBS 9941(T) by 8.8% nucleotide substitutions and from strain YE170(T) by 9.4% nucleotide substitutions. The result of pairwise sequence similarity of the D1/D2 and ITS1-2 regions together with phylogenetic analysis indicated that strains ST-78(T) and YE170(T) represented two novel species within the Yamadazyma clade. The names Yamadazyma insecticola f.a., sp. nov. (type strain ST-78(T) = BCC 8314(T) = NBRC 110421(T) = CBS 13382(T); MycoBank no. MB810546) and Yamadazyma epiphylla f.a., sp. nov. (type strain YE170(T) = BCC 63466(T) = NBRC 110423(T) = CBS 13384(T); MycoBank no. MB810547) are proposed for the two novel yeast species.

Wickerhamomyces tratensis sp. nov. and Candida namnaoensis sp. nov., two novel ascomycetous yeast species in the Wickerhamomyces clade found in Thailand.

Two closely related yeast strains, ST-382 and ST-392, isolated in Thailand showed intermediate relatedness in the DNA-DNA hybridization experiment suggesting that the two strains represent closely related distinct species. In the tree based on the D1/D2 domain sequences of the large subunit rRNA gene, the two strains are located in a subclade in the Wickerhamomyces clade with high bootstrap support. In the D1/D2 domain, the two strains differed by two nucleotides and are assumed to be very closely related. Strain ST-392(T) (=BCC 15102(T) = NBRC 107799(T) = CBS 12176(T) forming hat-shaped ascospores is described as Wickerhamomyces tratensis sp. nov. and strain ST-382(T) (= BCC 15093(T) = NBRC 107800(T) = CBS 12175(T) is described as Candida namnaoensis sp. nov. because ascospores are not found in this strain. In phenotypic characteristics, W. tratensis and C. namnaoensis are discriminated by the ability of alcoholic fermentation and the assimilation of galactose, D-xylose and D-gluconic acid.

Wickerhamomyces xylosica sp. nov. and Candida phayaonensis sp. nov., two xylose-assimilating yeast species from soil.

Two strains (NT29(T) and NT31(T)) of xylose-assimilating yeasts were obtained from soils collected in northern Thailand. On the basis of morphological, biochemical, physiological and chemotaxonomic characteristics, and sequence analysis of the D1/D2 domain of the large subunit rRNA gene and the internal transcribed spacer region, the two strains were found to represent two novel ascomycete yeast species. Strain NT29(T) was assigned to the genus Candida belonging to the Pichia clade as a representative of Candida phayaonensis sp. nov.; the type strain is NT29(T) (=BCC 47634(T)=NBRC 108868(T)=CBS 12319(T)). Strain NT31(T) represented a novel Wickerhamomyces species, which was named Wickerhamomyces xylosica sp. nov.; the type strain is NT31(T) (=BCC 47635(T)=NBRC 108869(T)=CBS 12320(T)).

Four novel species of the anamorphic yeast genus Candida found in Thailand and Taiwan.

Four strains of yeasts isolated in Thailand and Taiwan were found to represent four distinct novel species of the ascomycetous anamorphic yeast genus Candida. These strains are located in the Clavispora-Metschnikowia clade in a phylogenetic tree based on the D1/D2 domain sequences of the large subunit rRNA genes. Together with Candida picinguabensis and Candida saopaulonensis, the four novel species constitute a well-separated subclade from other species of the Clavispora-Metschnikowia clade. Three species from Thailand are described as Candida bambusicola sp. nov. (type strain, ST-50(T) = BCC 7750(T) = NBRC 106734(T) = CBS 11723(T)), Candida nongkhaiensis sp. nov. (type strain, ST-95(T) = BCC 8331(T) = NBRC 105874(T) =CBS 11724(T)) and Candida succicola sp. nov. (type strain, ST-631(T) = BCC 15314(T) = NBRC 106736(T) = CBS 11726(T)), respectively, and the species from Taiwan is described as Candida touchengensis sp. nov. (type strain, SY4S03(T) = NBRC 102647(T) = BCRC 23097(T) = CBS 10585(T)).

Candida uthaithanina sp. nov., an anamorphic yeast species in Nakaseomyces clade isolated in Thailand.

Three yeast stains were isolated from two unknown fruits (strains DD2-22-1(T) and SK44) and moss (strain ST-449) in Thailand. Analysis of the D1/D2 domain of the large subunit (LSU) rRNA gene sequences of the three strains revealed that they belonged to the same species. In terms of pairwise sequence similarity, Candida cf. glabrata UWO(PS) 98-110.4 and Candida nivariensis were the closest undescribed and recognized taxa, but the levels of nucleotide substitutions were 1.7-1.9% and 2.0-2.2%, respectively. The levels of nucleotide substitutions were sufficient to justify the description of a separate species of Candida. In the phylogenetic tree based on the D1/D2 domain of the LSU rRNA gene the three strains were placed in a separate branch in the Nakaseomyces clade with C. cf. glabrata UWO(PS)98-110.4, C. nivariensis, Candida glabrata, Candida bracarensis, Candida kungkrabaensis and Nakaseomyces delphensis. Phenotypic characteristics of the three strains were similar which included proliferation by multilateral budding, absence of ascospores, arthrospores or ballistospores; negative for Diazonium blue B and urease tests. The major ubiquinone was Q-6. On the basis of the above findings, the three strains were assigned to a single novel species of Candida, for which the name Candida uthaithanina sp. nov is proposed. The type strain is DD2-22-1(T) (= BCC 29899(T) = NBRC 104876(T) = CBS 10932(T)).

Candida saraburiensis sp. nov. and Candida prachuapensis sp. nov., xylose-utilizing yeast species isolated in Thailand.

Four strains of two novel xylose-utilizing yeast species were obtained from samples collected in Thailand from decaying corncobs (strains KU-Xs13(T) and KU-Xs18), a decaying grass (KU-Xs20) and estuarine water from a mangrove forest (WB15(T)). On the basis of morphological, biochemical, physiological and chemotaxonomic characteristics and sequence analysis of the D1/D2 domain of the large subunit rRNA gene, the four strains were found to represent two novel species of the genus Candida in the Candida albicans/Lodderomyces elongisporus clade. Three strains (KU-Xs13(T), KU-Xs18 and KU-Xs20) were assigned as a single novel species, which was named Candida saraburiensis sp. nov. The type strain is KU-Xs13(T) (=CBS 11696(T)=NBRC 106721(T)=BCC 39601(T)). Strain WB15(T) represented another novel species of the genus Candida that was named Candida prachuapensis sp. nov. The type strain is WB15(T) (=CBS 11024(T)=NBRC 104881(T)=BCC 29904(T)).

Candida xylanilytica sp. nov., a xylan-degrading yeast species isolated from Thailand.

Xylan is a major component of hemicellulose, which constitutes about 40 % of plant biomass. Hydrolysis of xylan into simple sugars is one of the important steps in the conversion of lignocellulosic material to value-added products. During an investigation of cellulose- and xylan-degrading yeasts, two yeast strains that were able to use cellulose and xylan as sole carbon source were found to represent a phylogenetically distinct species in the Spathaspora clade. The closest species in terms of pairwise sequence similarity in the D1/D2 domain of the LSU rRNA gene was Candida subhashii. The novel species can be distinguished from the other species in the Spathaspora clade based on the ability to assimilate methanol and raffinose, growth in medium containing 60 % glucose, and growth at 42 °C. It ferments glucose but not other carbohydrates. The name Candida xylanilytica sp. nov. is proposed for this species. The type strain is KU-Xn11(T) ( = NBRC 106499(T)  = BCC 34694(T)  = CBS 11761(T)).

Candida andamanensis sp. nov., Candida laemsonensis sp. nov. and Candida ranongensis sp. nov., anamorphic yeast species isolated from estuarine waters in a Thai mangrove forest.

Five strains (RV5(T), RV140, R31(T), RS17 and RS28(T)) representing three novel anamorphic ascomycetous yeast species were isolated by membrane filtration from estuarine waters collected from a mangrove forest in Laem Son National Park, Ranong Province, Thailand, on different occasions. On the basis of morphological, biochemical, physiological and chemotaxonomic characteristics, sequence analysis of the D1/D2 domain of the large-subunit rRNA gene and the internal transcribed spacer region and phylogenetic analysis, three strains were found to represent two novel Candida species. Two strains (RV5(T) and RV140) represented a single novel species, for which the name Candida laemsonensis sp. nov. is proposed. The type strain is RV5(T) (=BCC 35154(T) =NBRC 105873(T) =CBS 11419(T)). Strain R31(T) was assigned to a novel species that was named Candida andamanensis sp. nov. (type strain R31(T) =BCC 25965(T) =NBRC 103862(T) =CBS 10859(T)). On the basis of morphological, biochemical, physiological and chemotaxonomic characteristics, sequence analysis of the D1/D2 domain of the large-subunit rRNA gene and phylogenetic analysis, strains RS17 and RS28(T) represented another novel species of Candida, for which the name Candida ranongensis sp. nov. is proposed. The type strain is RS28(T) (=BCC 25964(T) =NBRC 103861(T) =CBS 10861(T)).

Candida potacharoeniae sp. nov. and Candida spenceri sp. nov., two novel galactose-containing ascomycetous anamorphic yeast species isolated in Thailand.

Fifteen strains of anamorphic yeasts isolated from various natural substrates collected in various places in Thailand were found to represent two novel species of anamorphic yeast genus Candida based on the sequence analysis of the D1/D2 domain of the large subunit rRNA genes, chemotaxonomic and conventional properties used for the classification of yeasts. These strains are located in the clade including Candida etchellsii and Candida magnoliae. Fourteen strains represented by ST-490(T) (BCC 15176(T)=NBRC 106439(T)= CBS 11674(T)) are closely related to Candida sorbosivorans in the D1/D2 sequences but 11 nucleotides (2.4%) were substituted. The remaining strain, ST-594(T) (=BCC 15278(T)=NBRC 106446(T)=CBS 11673(T)) showed a close relationship to Candida geochares but 21 nucleotides (4.7%) were substituted. Apparently, these strains represent two novel Candida species of the Starmerella clade. The two species are described as Candida potacharoeniae sp. nov. and Candida spenceri sp. nov. in the present paper. Like the most species of this clade, the two species contain galactose in the cells in addition to glucose and mannose and have high mol% G + C of 54.4-55.9 and 54.9, respectively.

Candida asiatica sp. nov., an anamorphic ascomycetous yeast species isolated from natural samples from Thailand, Taiwan, and Japan.

Six yeast strains of a novel anamorphic yeast species were isolated from natural samples collected in Thailand (RV60(T) and LYSM9), Taiwan (SC5L04 and GE19S05), and Japan (JCM 11058 and JCM 11059). Analysis of the D1/D2 domain of the large subunit rRNA gene sequences revealed that the sequences of five strains (LYSM9, SC5L04, GE19S05, JCM 11058, and JCM 11059) were identical and differed from the sequence of strain RV60(T) by only one nucleotide substitution. The closest recognized species in terms of pairwise sequence similarity was Candida abiesophila, but the level of nucleotide substitution (14.2-14.3%) was sufficient to justify the description of a separate species. Phenotypic characteristics of the six strains were almost the same except for two strains from Japan, which showed the ability to ferment glucose and grew in the presence of 10% NaCl and 5% glucose while the others did not. The phenotypic characteristics of the six strains included proliferation by multilateral budding, absence of ascospores, arthrospores, and ballistospores, and negative Diazonium blue B and urease tests. The major ubiquinone was Q-7. On the basis of the above findings, the six strains were assigned to a single novel species of Candida, for which the name Candida asiatica sp. nov. is proposed. The type strain is RV60(T) (BCC 25966(T) = NBRC 103863(T) = CBS 10863(T)).