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Identification of furfural resistant strains of Saccharomyces cerevisiae and Saccharomyces paradoxus from a collection of environmental and industrial isolates.

Field SJ, Ryden P, Wilson D, James SA, Roberts IN, Richardson DJ, Waldron KW, Clarke TA - Biotechnol Biofuels (2015)

Bottom Line: Furthermore, ethanol production in this strain did not appear to be inhibited by furfural, with the highest ethanol yield observed at 3.0 mg ml(-1) furfural.Although furfural resistance was not found to be a trait specific to any one particular lineage or population, three of the strains were isolated from environments where they might be continually exposed to low levels of furfural through the ongoing natural degradation of lignocelluloses, and would therefore develop elevated levels of resistance to these furan compounds.Thus, these strains represent good candidates for future studies of genetic variation relevant to understanding and manipulating furfural resistance and in the development of tolerant ethanologenic yeast strains for use in bioethanol production from lignocellulose processing.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of East Anglia, Norwich, NR4 7JN UK.

ABSTRACT

Background: Fermentation of bioethanol using lignocellulosic biomass as a raw material provides a sustainable alternative to current biofuel production methods by utilising waste food streams as raw material. Before lignocellulose can be fermented, it requires physical, chemical and enzymatic treatment in order to release monosaccharides, a process that causes the chemical transformation of glucose and xylose into the cyclic aldehydes furfural and hydroxyfurfural. These furan compounds are potent inhibitors of Saccharomyces fermentation, and consequently furfural tolerant strains of Saccharomyces are required for lignocellulosic fermentation.

Results: This study investigated yeast tolerance to furfural and hydroxyfurfural using a collection of 71 environmental and industrial isolates of the baker's yeast Saccharomyces cerevisiae and its closest relative Saccharomyces paradoxus. The Saccharomyces strains were initially screened for growth on media containing 100 mM glucose and 1.5 mg ml(-1) furfural. Five strains were identified that showed a significant tolerance to growth in the presence of furfural, and these were then screened for growth and ethanol production in the presence of increasing amounts (0.1 to 4 mg ml(-1)) of furfural.

Conclusions: Of the five furfural tolerant strains, S. cerevisiae National Collection of Yeast Cultures (NCYC) 3451 displayed the greatest furfural resistance and was able to grow in the presence of up to 3.0 mg ml(-1) furfural. Furthermore, ethanol production in this strain did not appear to be inhibited by furfural, with the highest ethanol yield observed at 3.0 mg ml(-1) furfural. Although furfural resistance was not found to be a trait specific to any one particular lineage or population, three of the strains were isolated from environments where they might be continually exposed to low levels of furfural through the ongoing natural degradation of lignocelluloses, and would therefore develop elevated levels of resistance to these furan compounds. Thus, these strains represent good candidates for future studies of genetic variation relevant to understanding and manipulating furfural resistance and in the development of tolerant ethanologenic yeast strains for use in bioethanol production from lignocellulose processing.

No MeSH data available.


Related in: MedlinePlus

Growth curves ofS. cerevisiaeNCYC 2826 measured by optical density at 600 nm. Data shown are the average of three replicate experiments. (A, C) Growth using 10% wheat straw hydrolysate only (squares), 10% wheat straw hydrolysate and YNB (circles), or 10% wheat straw hydrolysate and 2.3 mg ml−1 urea (triangles). (B, D) Growth in media containing 2.3 mg ml−1 urea and initial wheat straw concentrations of 5% (squares), 10% (closed circles), 15% (triangle) or 20% (open circle). OD, optical density; hr, hour.
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Fig1: Growth curves ofS. cerevisiaeNCYC 2826 measured by optical density at 600 nm. Data shown are the average of three replicate experiments. (A, C) Growth using 10% wheat straw hydrolysate only (squares), 10% wheat straw hydrolysate and YNB (circles), or 10% wheat straw hydrolysate and 2.3 mg ml−1 urea (triangles). (B, D) Growth in media containing 2.3 mg ml−1 urea and initial wheat straw concentrations of 5% (squares), 10% (closed circles), 15% (triangle) or 20% (open circle). OD, optical density; hr, hour.

Mentions: Figure 1A shows the growth of S. cerevisiae National Collection of Yeast Cultures (NCYC) 2826 grown at 30°C for 36 h in a culture containing a hydrolysate with a glucose concentration of 123 mM prepared as described in the ‘Methods’ section. The S. cerevisiae strain was chosen due to its reported high ethanol tolerance and robustness in industrial fermentations. Figure 1A shows that when S. cerevisiae NCYC 2826 was grown on wheat straw hydrolysate alone there was a slow growth rate μ of 0.036 h−1 and a final optical density (OD) of 0.8. Addition of Yeast nutrient base (YNB) to the media caused an increase in μ to 0.135 h−1 and a final OD of 1.5, while addition of 2.3 mg ml−1 urea to the wheat straw hydrolysate gave a μ of 0.99 h−1 and a final OD of 1.3. Previous studies have shown that urea supplements can increase ethanol production in yeast fermentation and that urea itself is an essential component in the most minimal yeast growth media [16,17]. Our results support these earlier findings, confirming the requirement of urea for near-optimal growth of yeast. After 36 h, the ethanol concentration in the cultures was measured and the yield of ethanol obtained from 123 mM glucose was approximately 90% of the total theoretical yield for all cultures. While ethanol was produced to a comparable yield under these three culture conditions, the growth was slower and the final optical density less on wheat straw hydrolysate than when either urea or YNB was added to the culture. This suggests that although glucose was available for fermentation, the hydrolysate did not contain sufficient nutritional elements to allow the culture to divide at its maximal rate and achieve optimal density.Figure 1


Identification of furfural resistant strains of Saccharomyces cerevisiae and Saccharomyces paradoxus from a collection of environmental and industrial isolates.

Field SJ, Ryden P, Wilson D, James SA, Roberts IN, Richardson DJ, Waldron KW, Clarke TA - Biotechnol Biofuels (2015)

Growth curves ofS. cerevisiaeNCYC 2826 measured by optical density at 600 nm. Data shown are the average of three replicate experiments. (A, C) Growth using 10% wheat straw hydrolysate only (squares), 10% wheat straw hydrolysate and YNB (circles), or 10% wheat straw hydrolysate and 2.3 mg ml−1 urea (triangles). (B, D) Growth in media containing 2.3 mg ml−1 urea and initial wheat straw concentrations of 5% (squares), 10% (closed circles), 15% (triangle) or 20% (open circle). OD, optical density; hr, hour.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4389715&req=5

Fig1: Growth curves ofS. cerevisiaeNCYC 2826 measured by optical density at 600 nm. Data shown are the average of three replicate experiments. (A, C) Growth using 10% wheat straw hydrolysate only (squares), 10% wheat straw hydrolysate and YNB (circles), or 10% wheat straw hydrolysate and 2.3 mg ml−1 urea (triangles). (B, D) Growth in media containing 2.3 mg ml−1 urea and initial wheat straw concentrations of 5% (squares), 10% (closed circles), 15% (triangle) or 20% (open circle). OD, optical density; hr, hour.
Mentions: Figure 1A shows the growth of S. cerevisiae National Collection of Yeast Cultures (NCYC) 2826 grown at 30°C for 36 h in a culture containing a hydrolysate with a glucose concentration of 123 mM prepared as described in the ‘Methods’ section. The S. cerevisiae strain was chosen due to its reported high ethanol tolerance and robustness in industrial fermentations. Figure 1A shows that when S. cerevisiae NCYC 2826 was grown on wheat straw hydrolysate alone there was a slow growth rate μ of 0.036 h−1 and a final optical density (OD) of 0.8. Addition of Yeast nutrient base (YNB) to the media caused an increase in μ to 0.135 h−1 and a final OD of 1.5, while addition of 2.3 mg ml−1 urea to the wheat straw hydrolysate gave a μ of 0.99 h−1 and a final OD of 1.3. Previous studies have shown that urea supplements can increase ethanol production in yeast fermentation and that urea itself is an essential component in the most minimal yeast growth media [16,17]. Our results support these earlier findings, confirming the requirement of urea for near-optimal growth of yeast. After 36 h, the ethanol concentration in the cultures was measured and the yield of ethanol obtained from 123 mM glucose was approximately 90% of the total theoretical yield for all cultures. While ethanol was produced to a comparable yield under these three culture conditions, the growth was slower and the final optical density less on wheat straw hydrolysate than when either urea or YNB was added to the culture. This suggests that although glucose was available for fermentation, the hydrolysate did not contain sufficient nutritional elements to allow the culture to divide at its maximal rate and achieve optimal density.Figure 1

Bottom Line: Furthermore, ethanol production in this strain did not appear to be inhibited by furfural, with the highest ethanol yield observed at 3.0 mg ml(-1) furfural.Although furfural resistance was not found to be a trait specific to any one particular lineage or population, three of the strains were isolated from environments where they might be continually exposed to low levels of furfural through the ongoing natural degradation of lignocelluloses, and would therefore develop elevated levels of resistance to these furan compounds.Thus, these strains represent good candidates for future studies of genetic variation relevant to understanding and manipulating furfural resistance and in the development of tolerant ethanologenic yeast strains for use in bioethanol production from lignocellulose processing.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of East Anglia, Norwich, NR4 7JN UK.

ABSTRACT

Background: Fermentation of bioethanol using lignocellulosic biomass as a raw material provides a sustainable alternative to current biofuel production methods by utilising waste food streams as raw material. Before lignocellulose can be fermented, it requires physical, chemical and enzymatic treatment in order to release monosaccharides, a process that causes the chemical transformation of glucose and xylose into the cyclic aldehydes furfural and hydroxyfurfural. These furan compounds are potent inhibitors of Saccharomyces fermentation, and consequently furfural tolerant strains of Saccharomyces are required for lignocellulosic fermentation.

Results: This study investigated yeast tolerance to furfural and hydroxyfurfural using a collection of 71 environmental and industrial isolates of the baker's yeast Saccharomyces cerevisiae and its closest relative Saccharomyces paradoxus. The Saccharomyces strains were initially screened for growth on media containing 100 mM glucose and 1.5 mg ml(-1) furfural. Five strains were identified that showed a significant tolerance to growth in the presence of furfural, and these were then screened for growth and ethanol production in the presence of increasing amounts (0.1 to 4 mg ml(-1)) of furfural.

Conclusions: Of the five furfural tolerant strains, S. cerevisiae National Collection of Yeast Cultures (NCYC) 3451 displayed the greatest furfural resistance and was able to grow in the presence of up to 3.0 mg ml(-1) furfural. Furthermore, ethanol production in this strain did not appear to be inhibited by furfural, with the highest ethanol yield observed at 3.0 mg ml(-1) furfural. Although furfural resistance was not found to be a trait specific to any one particular lineage or population, three of the strains were isolated from environments where they might be continually exposed to low levels of furfural through the ongoing natural degradation of lignocelluloses, and would therefore develop elevated levels of resistance to these furan compounds. Thus, these strains represent good candidates for future studies of genetic variation relevant to understanding and manipulating furfural resistance and in the development of tolerant ethanologenic yeast strains for use in bioethanol production from lignocellulose processing.

No MeSH data available.


Related in: MedlinePlus