Diversity and Physiological Characterization of D-Xylose-Fermenting Yeasts Isolated from the Brazilian Amazonian Forest

Abstract

BackgroundThis 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.Methodology/Principal FindingsA 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/SignificanceThis 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.

Xylitol production by yeasts isolated from rotting wood in the Galápagos Islands, Ecuador, and description of Cyberlindnera galapagoensis f.a., sp. nov.

“…The tubes were incubated on an orbital shaker under the same conditions described above. After growth was detected, one loopful from each tube was streaked on YNB-D-xylose, YNB-xylan or YNB-CMC agar media (Cadete et al 2012). The plates were incubated at 25°C until colonies developed.…”

“…Conspecific isolates generally produce identical banding profiles using this PCRfingerprinting technique (Rosa et al 2007). Yeast strains with identical PCR fingerprinting patterns were grouped and putatively considered to belong to the same species (Cadete et al 2012). At least one representative strain from each EI1 group was subjected to sequence analysis of the D1/D2 region of the large subunit (LSU) of the rRNA gene and the ITS-5.8S rRNA gene region, directly from whole cells, as described previously (Lachance et al 1999).…”

“…However, despite the existence of xylitol-producing yeasts such as Candida tropicalis, Cyberlindnera saturnus, Debaryomyces hansenii, Meyerozyma guilliermondii and Pachysolen tannophilus (da Silva and Afschar 1994; Leathers and Gupta 1997;Converti et al 1999;Kamat et al 2013), one of the greatest challenges in xylitol production by biotechnology processes is the availability of strains able to produce high yields of this polyol in an industrial context. D-xylose-assimilating yeasts are closely associated with rotting wood in nature, and several new yeasts have been isolated from this substrate in ecosystems with high biodiversity rates (Cadete et al 2012;Morais et al 2013a, b).…”

Efficient production of second generation ethanol and xylitol by yeasts from Amazonian beetles (Coleoptera) and their galleries

“…During cofermentation, a variation of 89-95.44% was obtained (Table 4), which seems promising. Considering the results of Cadete et al (2012), who, with S. passalidarum in a medium with D-xylose (50 g.L -1 ) as the exclusive carbon source, obtained the maximum ethanol production in 24 h at a temperature of 30°C, with ethanol production ranging from 15 to 18 g.L -1 (Q P = 0.6 to 0.75 g.L.h -1…”

“…In fact, the gut of beetles and other insects is considered a hotspot of yeast diversity (Suh and Blackwell, 2004;Boekhout, 2005;Rivera et al, 2009;Cadete et al, 2009Cadete et al, , 2012Urbina et al, 2013;Gouliamova et al, 2015;Cadete et al, 2015Cadete et al, , 2016.…”