Abstract:The ortho-substituted 2-hydroxybenzaldehyde caused 20-fold stronger inhibition than meta- and para-substituted analogues of 3- and 4-hydroxybenzaldehydes.
“…This stimulatory effect could be resulted from the change of redox balance in C. beijerinckii , because NADPH or NADH was used to reduce furfural to furfural alcohol [ 38 ]. Aromatic aldehydes (such as benzaldehyde, 2-hydroxybenzaldehyde and vanillin) has been reported to limit the growth and butanol yield of C. acetobutylicum [ 39 ]. Fig.…”
Section: Resultsmentioning
confidence: 99%
“…RCM medium (38 g L −1 ) was autoclaved (121 °C) for 15 min and then sparged with nitrogen to remove the oxygen. The spores were heat-shock (75 °C) for 10 min, inoculated to the sterilized RCM medium (50 mL), and then incubated (35 °C) in anaerobic chamber for 16–18 h. The optical density (OD 600 ) was tested by UV–Vis spectrophotometer in terms of the absorption intensity at 600 nm to determine the cell concentration [ 39 ]. The cell was inoculated for fermentation with an OD 600 value of 1.30.…”
BackgroundBiomass prehydrolysates from dilute acid pretreatment contain a considerable amount of fermentable sugars for biofuels production. However, carbonyl degradation compounds present severe toxicity to fermentation microbes. Furans (such as furfural and hydroxymethylfurfural), aliphatic acids (such as acetic acid, formic acid and levulinic acid) and phenolic compounds (such as vanillin and syringaldehyde) have been suggested to be the main inhibitors in biomass prehydrolysates. However, no single compound has been determined as the dominant toxic inhibitor. The effects of various detoxification methods on inhibitors removal have not been fully understood.ResultsThe effects of overliming and activated carbon (AC) detoxification on the removal of inhibitors and butanol fermentation of the poplar prehydrolysates were investigated. Gas chromatography–mass spectrometry (GC/MS) was used to identify and quantify 46 carbonyl compounds as potential inhibitors. It was observed that overliming and AC treatment alone did not make the prehydrolysates fermentable with Clostridium saccharobutylicum. The sequential overliming and AC resulted in a remarkable fermentability and a high butanol yield at 0.22 g g−1 sugar. The inhibitor removal in the prehydrolysates treated by overliming and AC was also examined by GC/MS. Overliming removed 75.6% of furan derivatives and 68.1% of aromatic monomers. In comparison, AC (5.0% w/v) removed 77.9% of furan derivatives and 98.6% of aromatic monomers. In addition, overliming removed much more 2,5-furandicarboxyaldehyde, 5-ethylfuran-2-carbaldehyde and 2,5-hexanedione than AC did. On the contrary, AC could remove considerably more phenolic acids than overliming. In the sequential detoxification, both dialdehydes/diketones and phenolic acids were extensively removed. This could be the main reason why the sequential detoxification enabled a remarkable ABE fermentation for the prehydrolysates.ConclusionsThis study indicated that the effect of overliming and AC treatment on inhibitors removal was related to their chemical structures. Overliming removed more dialdehydes and diketones than AC treatment, while AC removed more phenolic acids than overliming. Sequential overliming and AC treatment were required to make the prehydrolysates fermentable with C. saccharobutylicum. The study also suggested different detoxification method was needed for ABE fermentation of the prehydrolysate as compared to ethanol fermentation.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1182-0) contains supplementary material, which is available to authorized users.
“…This stimulatory effect could be resulted from the change of redox balance in C. beijerinckii , because NADPH or NADH was used to reduce furfural to furfural alcohol [ 38 ]. Aromatic aldehydes (such as benzaldehyde, 2-hydroxybenzaldehyde and vanillin) has been reported to limit the growth and butanol yield of C. acetobutylicum [ 39 ]. Fig.…”
Section: Resultsmentioning
confidence: 99%
“…RCM medium (38 g L −1 ) was autoclaved (121 °C) for 15 min and then sparged with nitrogen to remove the oxygen. The spores were heat-shock (75 °C) for 10 min, inoculated to the sterilized RCM medium (50 mL), and then incubated (35 °C) in anaerobic chamber for 16–18 h. The optical density (OD 600 ) was tested by UV–Vis spectrophotometer in terms of the absorption intensity at 600 nm to determine the cell concentration [ 39 ]. The cell was inoculated for fermentation with an OD 600 value of 1.30.…”
BackgroundBiomass prehydrolysates from dilute acid pretreatment contain a considerable amount of fermentable sugars for biofuels production. However, carbonyl degradation compounds present severe toxicity to fermentation microbes. Furans (such as furfural and hydroxymethylfurfural), aliphatic acids (such as acetic acid, formic acid and levulinic acid) and phenolic compounds (such as vanillin and syringaldehyde) have been suggested to be the main inhibitors in biomass prehydrolysates. However, no single compound has been determined as the dominant toxic inhibitor. The effects of various detoxification methods on inhibitors removal have not been fully understood.ResultsThe effects of overliming and activated carbon (AC) detoxification on the removal of inhibitors and butanol fermentation of the poplar prehydrolysates were investigated. Gas chromatography–mass spectrometry (GC/MS) was used to identify and quantify 46 carbonyl compounds as potential inhibitors. It was observed that overliming and AC treatment alone did not make the prehydrolysates fermentable with Clostridium saccharobutylicum. The sequential overliming and AC resulted in a remarkable fermentability and a high butanol yield at 0.22 g g−1 sugar. The inhibitor removal in the prehydrolysates treated by overliming and AC was also examined by GC/MS. Overliming removed 75.6% of furan derivatives and 68.1% of aromatic monomers. In comparison, AC (5.0% w/v) removed 77.9% of furan derivatives and 98.6% of aromatic monomers. In addition, overliming removed much more 2,5-furandicarboxyaldehyde, 5-ethylfuran-2-carbaldehyde and 2,5-hexanedione than AC did. On the contrary, AC could remove considerably more phenolic acids than overliming. In the sequential detoxification, both dialdehydes/diketones and phenolic acids were extensively removed. This could be the main reason why the sequential detoxification enabled a remarkable ABE fermentation for the prehydrolysates.ConclusionsThis study indicated that the effect of overliming and AC treatment on inhibitors removal was related to their chemical structures. Overliming removed more dialdehydes and diketones than AC treatment, while AC removed more phenolic acids than overliming. Sequential overliming and AC treatment were required to make the prehydrolysates fermentable with C. saccharobutylicum. The study also suggested different detoxification method was needed for ABE fermentation of the prehydrolysate as compared to ethanol fermentation.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1182-0) contains supplementary material, which is available to authorized users.
“…S. cerevisiae is a traditionally competitive cell factory used for bioethanol production due to its superior tolerance to ethanol and low pH, as well as its ease of genetic manipulation [42]. To overcome vanillin toxicity as a barrier to reduced bioethanol-production costs, vanillin-tolerant strains have been screened and engineered [38,[43][44][45]; however, these strains have not fully resolved the problems of toxicity associated with lignin-derived phenolics, which have been documented in other fermentable microorganisms (i.e., ethanol fermentation by Thermoanaerobacter mathranii, butanol fermentation by Clostridium beijerinckii and Clostridium acetobutylicum, butyric acid fermentation by Clostridium tyrobutyricum, hydrogen fermentation by Thermoanaerobacter thermosaccharolyticum, bacterial nanocellulose [46][47][48][49][50][51][52]. Therefore, the presence of lignin-derived phenolics remains a problem in biorefining processes using lignocellulosic biomass.…”
Section: Table 1 Detected Vanillin-specific Compounds Derived From Oxmentioning
Background: Vanillin is the main byproduct of alkaline-pretreated lignocellulosic biomass during the process of fermentable-sugar production and a potent inhibitor of ethanol production by yeast. Yeast cells are usually exposed to vanillin during the industrial production of bioethanol from lignocellulosic biomass. Therefore, vanillin toxicity represents a major barrier to reducing the cost of bioethanol production. Results: In this study, we analysed the effects of oxygen-radical treatment on vanillin molecules. Our results showed that vanillin was converted to vanillic acid, protocatechuic aldehyde, protocatechuic acid, methoxyhydroquinone, 3,4-dihydroxy-5-methoxybenzaldehyde, trihydroxy-5-methoxybenzene, and their respective ring-cleaved products, which displayed decreased toxicity relative to vanillin and resulted in reduced vanillin-specific toxicity to yeast during ethanol fermentation. Additionally, after a 16-h incubation, the ethanol concentration in oxygen-radical-treated vanillin solution was 7.0-fold greater than that from non-treated solution, with similar results observed using alkalinepretreated rice straw slurry with oxygen-radical treatment. Conclusions: This study analysed the effects of oxygen-radical treatment on vanillin molecules in the alkaline-pretreated rice straw slurry, thereby finding that this treatment converted vanillin to its derivatives, resulting in reduced vanillin toxicity to yeast during ethanol fermentation. These findings suggest that a combination of chemical and oxygen-radical treatment improved ethanol production using yeast cells, and that oxygen-radical treatment of plant biomass offers great promise for further improvements in bioethanol-production processes.
“…The complete cell factory model comprises descriptions of biomass growth (aerobic and anaerobic respirations), nutrient consumption, DO dynamics, heterologous gene circuit enzyme production, and biotransformation enzymatic reactions. The inhibitory effects imposed by both the substrate and product (Li et al, 2017; Parke & Ornston, 2004), the lumped metabolic load resulted from the heterologous gene expressions (Borkowski et al, 2016), and the semi‐empirical link describing the growth‐associated bioproduction were also incorporated to better capture the system behavior. A schematic showing the different components in the complete cell model is illustrated in Figure 1.…”
Section: Methodsmentioning
confidence: 99%
“…From the cell growth profile, it is noticeable that the growth dampened immediately once the ferulic acid was added even when the resources like glycerol and oxygen were still in abundance. It has been stated that phenolic compounds such as ferulic acid at higher than 1 g/L exhibited complete arrest of cell growth (Li et al, 2017). Meanwhile, the intermediate feruloyl…”
Due to sustainability concerns, bio-based production capitalizing on microbes as cell factories is in demand to synthesize valuable products. Nevertheless, the nonhomogenous variations of the extracellular environment in bioprocesses often challenge the biomass growth and the bioproduction yield. To enable a more rational bioprocess optimization, we have established a model-driven approach that systematically integrates experiments with modeling, executed from flask to bioreactor scale, and using ferulic acid to vanillin bioconversion as a case study. The impacts of mass transfer and aeration on the biomass growth and bioproduction performances were examined using minimal small-scale experiments. An integrated model coupling the cell factory kinetics with the three-dimensional computational hydrodynamics of bioreactor was developed to better capture the spatiotemporal distributions of bioproduction. Full-factorial predictions were then performed to identify the desired operating conditions. A bioconversion yield of 94% was achieved, which is one of the highest for recombinant Escherichia coli using ferulic acid as the precursor.
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