Characterisation of the diversity and physiology of cellobiose-fermenting yeasts isolated from rotting wood in Brazilian ecosystems.

We investigated the yeast species associated with rotting wood samples obtained from Brazilian ecosystems, with a special focus on cellobiose-fermenting species. About 647 yeast strains were isolated from rotting wood samples collected from the areas of Atlantic rainforest, Cerrado, and Amazonian forest. Eighty-six known species and 47 novel species of yeasts were isolated. Candida boidinii, Cyberlindnera subsufficiens, Meyerozyma guilliermondii, Schwanniomyces polymorphus, Candida natalensis, and Debaryomyces hansenii were the most frequently isolated species. Among the cellobiose-fermenting yeasts, 14 known and three novel yeast species were identified. Scheffersomyces queiroziae, Sc. amazonensis, Yamadazyma sp.1, Hanseniaspora opuntiae, C. jaroonii, and Candida tammaniensis were the main ethanol-producing yeasts. These species also produced an intracellular ß-glucosidase responsible for cellobiose hydrolysis. In fermentation assays using a culture medium containing 50 g L-1 cellobiose, ethanol production was observed in all cases; Sc. queiroziae and Sc. amazonensis showed the highest yield, efficiency, and productivity. Candida jaroonii and Yamadazyma sp.1 strains also showed high efficiency in cellobiose fermentation, while C. tammaniensis and H. opuntiae strains produced low amounts of ethanol. This study shows the potential of rotting wood samples from Brazilian ecosystems as a source of yeasts, including new species as well as those with promising biotechnological properties.

Description of Hyphopichia buzzinii f.a., sp. nov. and Hyphopichia homilentoma comb. nov., the teleomorph of Candida homilentoma.

During studies of the yeast diversity associated with rotting wood in Brazil and fruits, plants and insects in French Guiana, three strains of a new species were isolated. Analysis of the sequences of the internal transcribed spacer (ITS)-5.8S and D1/D2 domains of the large subunit of the rRNA gene showed that this species belongs to the genus Hyphopichia and its closest relative is Candida homilentoma. These species differ by 44 nucleotide substitutions in D1/D2 sequences. A new species Hyphopichia buzzinii f. a., sp. nov., is proposed to accommodate these isolates. The type strain of Hyphopichia buzzinii sp. nov. is CLIB 1739T (=CBS 14300T = UFMG-CM-Y6121T; MycoBank number is MB 815609). In addition, we isolated 11 strains of C. homilentoma from rotting wood, leaf surfaces, and water bodies in Brazil, and these strains when crossed among one another and with the type strain (CBS 6312T) of this species, produced hat-shaped ascospores typical of the genus Hyphopichia. We describe the teleomorph of C. homilentoma as a new combination, Hyphopichia homilentoma comb. nov. (type strain CBS 6312T; MycoBank number is MB 820009). We also propose to transfer the other six Candida species of the Hyphopichia clade to this genus as new combinations. Hyphopichia homilentoma produced ethanol and xylitol from D-xylose whereas H. buzzinii was only able to convert this pentose to xylitol.

Saturnispora bothae sp. nov., isolated from rotting wood.

Two strains representing a novel species of the genus Saturnispora were isolated from rotting wood samples collected in an Atlantic Rainforest site in Brazil. Analyses of the sequences of the D1/D2 domains of the rRNA gene showed that this novel species belongs to a subclade in the Saturnispora clade formed by Saturnispora sanitii, Saturnispora sekii, Saturnispora silvae and Saturnisporasuwanaritii. The novel species differed in D1/D2 sequences by 60 or more nucleotide substitutions from these species. The strains produced asci with one to four hemispherical ascospores. A novel species named Saturnispora bothae sp. nov. is proposed to accommodate these isolates. The type strain is UFMG-CM-Y292T (=CBS 13484T). The MycoBank number is MB 817127.

Spencermartinsiella silvicola sp. nov., a yeast species isolated from rotting wood.

Three strains of a new xylanase-producing yeast species were isolated from rotting wood samples collected in the Atlantic Rain Forest of Brazil. The sequences of the internal transcribed spacer region and D1/D2 domains of the large subunit of the rRNA gene showed that this novel yeast species belongs to the genus Spencermartinsiella, and its closest relatives among recognized species are Spencermartinsiella europaea and Spencermartinsiella ligniputridi. A novel species, named Spencermartinsiella silvicola sp. nov., is proposed to accommodate these isolates. The type strain is UFMG-CM-Y274T ( = CBS 13490T). The MycoBank number is MB 813053. In addition, Candida cellulosicola is reassigned to the genus Spencermartinsiella as a new combination.

Identification and characterisation of xylanolytic yeasts isolated from decaying wood and sugarcane bagasse in Brazil.

In this study, yeasts associated with lignocellulosic materials in Brazil, including decaying wood and sugarcane bagasse, were isolated, and their ability to produce xylanolytic enzymes was investigated. A total of 358 yeast isolates were obtained, with 198 strains isolated from decaying wood and 160 strains isolated from decaying sugarcane bagasse samples. Seventy-five isolates possessed xylanase activity in solid medium and were identified as belonging to nine species: Candida intermedia, C. tropicalis, Meyerozyma guilliermondii, Scheffersomyces shehatae, Sugiyamaella smithiae, Cryptococcus diffluens, Cr. heveanensis, Cr. laurentii and Trichosporon mycotoxinivorans. Twenty-one isolates were further screened for total xylanase activity in liquid medium with xylan, and five xylanolytic yeasts were selected for further characterization, which included quantitative analysis of growth in xylan and xylose and xylanase and ß-D-xylosidase activities. The yeasts showing the highest growth rate and cell density in xylan, Cr. laurentii UFMG-HB-48, Su. smithiae UFMG-HM-80.1 and Sc. shehatae UFMG-HM-9.1a, were, simultaneously, those exhibiting higher xylanase activity. Xylan induced the highest level of (extracellular) xylanase activity in Cr. laurentii UFMG-HB-48 and the highest level of (intracellular, extracellular and membrane-associated) ß-D-xylosidase activity in Su. smithiae UFMG-HM-80.1. Also, significant ß-D-xylosidase levels were detected in xylan-induced cultures of Cr. laurentii UFMG-HB-48 and Sc. shehatae UFMG-HM-9.1a, mainly in extracellular and intracellular spaces, respectively. Under xylose induction, Cr. laurentii UFMG-HB-48 showed the highest intracellular ß-D-xylosidase activity among all the yeast tested. C. tropicalis UFMG-HB 93a showed its higher (intracellular) ß-D-xylosidase activity under xylose induction and higher at 30 °C than at 50 °C. This study revealed different xylanolytic abilities and strategies in yeasts to metabolise xylan and/or its hydrolysis products (xylo-oligosaccharides and xylose). Xylanolytic yeasts are able to secrete xylanolytic enzymes mainly when induced by xylan and present different strategies (intra- and/or extracellular hydrolysis) for the metabolism of xylo-oligosaccharides. Some of the unique xylanolytic traits identified here should be further explored for their applicability in specific biotechnological processes.

Sugiyamaella xylanicola sp. nov., a xylan-degrading yeast species isolated from rotting wood.

Four strains of a novel yeast species were isolated from rotting-wood samples in an Atlantic rainforest site in the state of Minas Gerais, Brazil. These yeasts were obtained from enrichments using yeast nitrogen base (YNB)-d-xylose or YNB-xylan media. The novel yeast species produces bacilliform ascospores typical of the genus Sugiyamaella, and its closest described relative in terms of sequence similarity is Candida (iter. nom. Sugiyamaella) marionensis. The yeast is able to grow in medium with xylan as sole carbon source and produces extracellular enzymes with xylanolytic activities. The novel species Sugiyamaella xylanicola sp. nov. is proposed to accommodate these isolates. The type strain is UFMG-CA-32.1(T) (=CBS 12683(T) =CBMAI 1467(T)).