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Johan Thevelein
KU Leuven
Lab of Molecular Cell Biology
New Delhi
12 March 2019
Development of yeast
strains for production of
second-generation
bioethanol and bio-based
chemicals
2G bioethanol and bio-chemicals production
Bioenergy crops
Waste streams
Forest residues
Recycled paper
Corn cob & stover
Bagasse
Wheat straw
Empty fruit bunches + many other potential feedstocks
Rice straw
• 1G Bioethanol
• Sugar
• Biomass
1G and 2G bioethanol production
1G YEAST
2G YEAST • 2G Bioethanol
Main challenges
• Efficient xylose fermentation
• High inhibitor tolerance
Engineering of S. cerevisiae for xylose fermentation
Eubacterium species: VIB/GlobalYeast (IP)
Two pathways
• Xylose reductase (fungal pathway):
redox problem xylitol accumulation
• Xylose isomerase (bacterial pathway)
difficult expression in yeast
Xylose isomerase expression in yeast
• Proprietary xylose isomerase
• Many gene copies high xylose isomerase activity
• Few other xylose isomerases are active in yeast very tight IP space small
number of commercial proprietary 2G bioethanol strains
• proprietary 2G yeast: bottleneck 2G bioethanol + 2G bio-based chemicals
Engineering of S. cerevisiae for high inhibitor tolerance
• Acetic acid
• Furfural and hydroxymethylfurfural corresponding alcohols
high toxicity low toxicity
medium
HAc
H+ + Ac- pH ±5
pH ±7
ATP ATP
Reductases
Export pumps
Improvement by targeted and random engineering:
(site-directed) mutagenesis, evolutionary adaptation, genome shuffling,
whole-genome transformation
Cheaper pretreatment methodologies higher inhibitor
levels more robust yeast cheaper process
Pooled
Extraction of genomic DNA
Whole-genome sequence analysis (Illumina)
Polygenic analysis platform for complex traits:
pooled-segregant whole-genome sequence analysis
2 parent strains QTL mapping (Quantitative Trait Locus)
min. ± 30 segr.
Screen of S. cerevisiae strain collection
Diploid strain with superior trait
Industrial diploid strain with inferior trait
Acetic acid tolerance of fermentation
Known:
Haa1: transcription factor
involved in acetic acid
tolerance
New:
Cup2: homolog of Haa1
Dot5
Glo1
Vma7
F1 segregants
F7 segregants
HAA1* : unique
mutation in acetic
acid tolerant strain
0% Acetic acid 1% Acetic acid
2.0% Acetic acid 1.6% Acetic acid
1.4% Acetic acid 1.2% Acetic acid
Insertion of G A mutation in HAA1 (2 alleles) of T18
● T18 HAA1*
○ T18
Predictable
improvement of stress tolerance
Industrial strains with high xylose fermentation capacity
Further improvement by evolutionary adaptation, genome shuffling, targeted genetic engineering with superior alleles, whole-genome transformation steady improvement of performance
ethanol glucose
xylose
Semi-anaerobic static fermentation in bagasse
hydrolysate
Goal for commercial E2G production
> 80% of sugar in 48 h with 1 g DW yeast/L and > 5% (v/v) ethanol titer
2G bioethanol and bio-chemicals production
Other major challenges
• Pretreatment of the biomass robustness of machinery
• Enzymatic hydrolysis ±20% of the cost of the ethanol
E2G yeast with secreted enzymes
- reduce enzyme requirement
- Holy grail: ‘Consolidated bioprocessing’
yeast: enzymatic hydrolysis + fermentation
Cellulolytic enzymes:
• β-glucosidase (BGL)
• Endoglucanase (EG)
• Cellobiohydrolase I (CBH I)
• Cellobiohydrolase II (MCBH II)
Hemicellulolytic enzymes:
• β-xylosidase (β-XYL)
• Xylanase (XYN)
Types of enzymes required
0 10 20 30 400
1
2
3
4
5
6
Time (h)
Co
mp
on
en
t (%
)
HPLC analysis of components during fermentation by MD4 and AC1 at 35°C
YP + 5% Glucose + 4% Xylose + 1% Cellobiose
Cellobiose AC1
Glucose AC1
Xylose AC1
Ethanol AC1
Cellobiose MD4
Glucose MD4
Xylose MD4
Ethanol MD4
Glucose
Xylose Cellobiose
Ethanol
MD4
MD4 with beta-glucosidase
Secreted ß-glucosidase (SfBGL1) supports cellobiose
fermentation
No negative effect of
ß-glucosidase expression on
glucose or xylose fermentation
MD4
MD4 with beta-glucosidase
Expression of beta-glucosidase results in efficient cellobiose utilization
50 mL YP + Xn4%
35°C
120rpm
0 25 50 75 1000.00
0.25
0.50
0.75
1.00
1.25
1.50
Time (h)
Weig
ht
loss (
%)
Fermentation of YPXn4 by MD4, AC1 and AC235°C, 120rpm, 1g/L
MD4
AC1
AC2.1
AC2.2
MD4: parent
AC1: MD4-TrBGL1
AC2: MD4-TrBGL1-AnXlnD-TrXyn2
AC2 strain: secreted β-xylosidase (AnXlnD) and xylanase
(TrXyn2) support xylan fermentation
AC2: Xylan is consumed
Parent strains do
not degrade xylan
4% Xylan + yeast extract/peptone
0 24 48 72 96 120
144
168
192
216
0
200
400
600
800
1000
Time (h)
mg
/L
PCA
0 24 48 72 96 120
144
168
192
216
0
500
1000
1500
2000
2500
3000
Time (h)
mg
/L
Muconic acid
Production of muconic acid with glucose + xylose mixture
20 mL CSM-FWY +Glucose (2.2%) + Xylose (2%) + EtOH (1%) + citrate buffer (0.1M, pH 5.5) in shaking flasks (300 ml), 250 RPM at 30°C. Start OD660: 1
PCA (500 mg/L) and muconic acid (2300 mg/L) from glucose + xylose
Sugars PCA Catechol Muconic acid
Muconic Acid pathway
Glucose (2.2%) + Xylose (2%)
Conclusions
Efficient industrial yeast strains for second-generation bioethanol production available: xylose utilization + high inhibitor tolerance Can still be improved further for better performance in undetoxified lignocellulose hydrolysates cheaper pretreatment technologies Strong platform for secreted enzyme expression Reduction of enzyme load/cost - Consolidated BioProcessing Strong platform for cell factory strains to produce bio-based chemicals with lignocellulosic biomass
2G bioethanol and bio-chemicals production
Thank you for your
attention