Diversity and physiological characterization of D-xylose-fermenting yeasts isolated from the Brazilian Amazonian Forest.
BACKGROUND
This study is the first to investigate the Brazilian Amazonian Forest to identify new D-xylose-fermenting yeasts that might potentially be used in the production of ethanol from sugarcane bagasse hemicellulosic hydrolysates.


RESULTS
A total of 224 yeast strains were isolated from rotting wood samples collected in two Amazonian forest reserve sites. These samples were cultured in yeast nitrogen base (YNB)-D-xylose or YNB-xylan media. Candida tropicalis, Asterotremella humicola, Candida boidinii and Debaryomyces hansenii were the most frequently isolated yeasts. Among D-xylose-fermenting yeasts, six strains of Spathaspora passalidarum, two of Scheffersomyces stipitis, and representatives of five new species were identified. The new species included Candida amazonensis of the Scheffersomyces clade and Spathaspora sp. 1, Spathaspora sp. 2, Spathaspora sp. 3, and Candida sp. 1 of the Spathaspora clade. In fermentation assays using D-xylose (50 g/L) culture medium, S. passalidarum strains showed the highest ethanol yields (0.31 g/g to 0.37 g/g) and productivities (0.62 g/L · h to 0.75 g/L · h). Candida amazonensis exhibited a virtually complete D-xylose consumption and the highest xylitol yields (0.55 g/g to 0.59 g/g), with concentrations up to 25.2 g/L. The new Spathaspora species produced ethanol and/or xylitol in different concentrations as the main fermentation products. In sugarcane bagasse hemicellulosic fermentation assays, S. stipitis UFMG-XMD-15.2 generated the highest ethanol yield (0.34 g/g) and productivity (0.2 g/L · h), while the new species Spathaspora sp. 1 UFMG-XMD-16.2 and Spathaspora sp. 2 UFMG-XMD-23.2 were very good xylitol producers.


CONCLUSIONS
This study demonstrates the promise of using new D-xylose-fermenting yeast strains from the Brazilian Amazonian Forest for ethanol or xylitol production from sugarcane bagasse hemicellulosic hydrolysates.
Departamento de Microbiologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
Raquel M
RM
Cadete
Monaliza A
MA
Melo
Kelly J
KJ
Dussán
Rita C L B
RC
Rodrigues
Silvio S
SS
Silva
Jerri E
JE
Zilli
Marcos J S
MJ
Vital
Fátima C O
FC
Gomes
Marc-André
MA
Lachance
Carlos A
CA
Rosa
D001938:Brazil; D002482:Cellulose / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D014644:Genetic Variation; D016133:Polymerase Chain Reaction; D013045:Species Specificity; D014197:Trees / Q000382:microbiology*; D014993:Xylitol / Q000096:biosynthesis; D014994:Xylose / Q000378:metabolism*; D015003:Yeasts / Q000235:genetics* / Q000378:metabolism*
D017931:DNA Primers; D000431:Ethanol; D002482:Cellulose; C027433:bagasse; D014994:Xylose; D014993:Xylitol