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Conversion of Biomass
Published in Jean-Luc Wertz, Philippe Mengal, Serge Perez, Biomass in the Bioeconomy, 2023
Jean-Luc Wertz, Philippe Mengal, Serge Perez
Succinic acid is synthesized as one of the mixed-acid fermentation products. Mixed acid fermentation produces a mixture of products including succinic acid, ethanol, lactic acid, formic acid, and acetic acid, from which the succinic acid must be isolated.69
Metabolic Engineering for the Production of a Variety of Biofuels and Biochemicals
Published in Kazuyuki Shimizu, Metabolic Regulation and Metabolic Engineering for Biofuel and Biochemical Production, 2017
Under micro aerobic or anaerobic conditions, a mixed-acid fermentation occurs in E. coli, forming such metabolites as lactate, acetate, formate, ethanol, CO2, and succinate. Most of the metabolites are produced from pyruvate, while succinate is produced from PEP through OAA, and therefore, one approach to the selective production of succinate is to reduce pyruvate production by disrupting ptsG which encodes EIIBCGlc of the PTS, and pykFA genes in E. coli (Lee et al. 2005). The resulting strain produced 0.35 moles of succinate/mole glucose. Simultaneous overexpression of the ppc gene of Sorghum vulgare (which encodes Ppc resistant to feedback inhibition by malate) and of the pyc gene of Lactococcus lactis in E. coli increased the succinate yield to 0.91 moles/mole glucose with a concomitant decrease in the lactate formation (Lin, San, et al., 2005a). Additional disruption of such genes as ldhA, ackA and pta increased the succinate yield to 0.3 g/g glucose (Lin, San, et al., 2005a). Further improvement may be made by deletion of the adhE and ldhA genes, and by overexpression of the pyc gene obtained from L. lactis, where it increased the yield to 1.3 moles of succinate/mole glucose (Sanchez et al. 2005a). The result indicates that inactivation of adhE is effective in increasing the use of reducing equivalents for the formation of succinate. The glyoxylate pathway may be utilized as an alternative route to succinate formation by deleting iclR gene, where IclR represses the aceBAK operon (Sanchez et al. 2005b). The utilization of the glyoxylate pathway together with the Ppc pathway for succinate production requires less reducing equivalents. The strain lacking the genes iclR, ldhA, adhE, and ackA, pta genes with overexpression of the pyc gene (from L. lactis) gave a succinate yield of 1.6 moles/mole glucose with the production of small amounts of formate and acetate. Further metabolic engineering with metabolic evolution gave higher succinate production by ldhA, adhE, ackA, focA, pflB mutant and ldhA, adhE, ackA, focA, pflB, mgsA, poxB mutant (Fig. 12) (Jantama et al. 2008).
Bioremediation of artificially contaminated soil with petroleum using animal waste: cow and poultry dung
Published in Cogent Engineering, 2020
O. Olawale, K. S. Obayomi, S. O. Dahunsi, O. Folarin
Biochemical test was carried out to identify the microbes involved in the reactions. The tests include citrate test, methyl red (MR) and Voges–Proskauer (VP). Citrate utilization test was carried out by preparation of slopes of the medium (Simmon’s citrate agar) in bijou bottle as instructed by the manufacturer. Using a sterile inoculating loop, the test organism was streaked on the medium and incubated at 37°C for 24 h. After incubation, the observation of a blue color indicates that the organism can utilize citrate while no color change indicates that such an organism cannot utilize citrate. The methyl red test was carried out to determine whether the microbe performs mixed acid fermentation when supplied with glucose. The microorganism is inoculated with MR broth and incubated for 4 days. FIve drops of methyl red indicator solution were added. A positive response is when the medium turns from yellow to red. Positive control microorganism includes E. coli. Voges–Proskauer test is to determine if an organism produces acetyl methyl carbinol from glucose fermentation. The microorganism is incubated at 37°C for 24 h. Add two drops of Barrit’s reagent. A positive response is when it changes from yellow to a pink-red color after 30 min of shaking vigorously.
Optimization of fermentation condition for co-production of ethanol and 2,3-butanediol (2,3-BD) from hemicellolosic hydrolysates by Klebsiella oxytoca XF7
Published in Chemical Engineering Communications, 2018
Anamika Sharma, Vikrant Nain, Rameshwar Tiwari, Surender Singh, Lata Nain
The highest production of 2,3-BD (12.18 ± 0.08 mg ml−1) and ethanol (4.08 ± 0.03 mg ml−1) was observed with 96.65% xylose consumption by the bacterial strain. Hence, K. oxytoca XF7 was able to ferment 96.65% of xylose from hemicellulose hydrolysate into ethanol and 2,3-BD production. The 2,3-BD and ethanol produced via mixed acid fermentation from pyruvic acid and various other metabolic intermediates, e.g., acetic acid, lactic acid, acetoin and succinic acid were also detected during the fermentation. Also, the level of these biofuel molecules can be increased by reducing the byproducts formation through metabolic engineering of K. oxytoca XF7, as reported by other researchers (Zhang et al., 2010; Li et al., 2015). The high pentose fermentation efficiency from lignocellulosic biomass hydrolysate revealed the superiority of K. oxytoca XF7 as a more promising industrial candidate for biofuel production.
Potential use of thermophilic bacteria for second-generation bioethanol production using lignocellulosic feedstocks: a review
Published in Biofuels, 2023
Much of the current research focuses on fermentation using mesophilic organisms, like Saccharomyces cerevisiae and Zymomonas mobilis, which can survive below 45 °C. However, the major drawbacks of using these microbes are incomplete utilisation of sugars and contamination. Certain mesophilic microbial strains like Pichia stipitis, Candida shehatae have been identified that can utilise C-5 sugars like xylose and arabinose. However, industrially suitable strains are yet to be identified and developed for large-scale production since they cannot produce bioethanol as the primary end product [16–18]. The most feasible option to overcome such limitations is using thermophilic bacteria, which have various advantages over their mesophilic counterparts. Thermophilic bacteria are considered safe as they are placed in the lowest microbial risk class. They can utilise a wide range of carbon sources, including C-5 ad C-6 sugars, and produce various thermostable enzymes making their use in second-generation ethanol production highly attractive [18,19]. The high temperature allows continuous ethanol removal and recovery and lowers oxygen solubility. Furthermore, the higher temperature lowers the chances of contamination, and the cost of cooling and increases the diffusion of nutrients, thereby increasing productivity [20]. However, low tolerance to bioethanol, low bioethanol yields and mixed acid fermentation are some of the significant disadvantages of thermophilic bacteria for their use on an industrial scale. This review comprehensively summarizes the metabolic advantages of thermophiles and the advances in overcoming the drawbacks of using thermophilic bacteria for bioethanol production. It also provides an overview of the research advancements of thermophilic bacteria using LCB as the substrate for bioethanol production.