Bioscience Evidence 2024, Vol.14, No.4, 143-153 http://bioscipublisher.com/index.php/be 149 5.3 Case study 3: methanogens for acetic acid production Methanogens have been investigated for their potential to produce acetic acid from CO2 through various metabolic pathways. The exploration of these pathways involves understanding the enzymatic mechanisms and optimizing reactor designs to enhance CO2 fixation and conversion efficiency. For instance, the use of bioreactors with optimized gas and photon transfer rates has been shown to improve the performance of microbial CO2 assimilation processes (Liebal et al., 2018). The sustainability and cost-effectiveness of using methanogens for acetic acid production are evaluated based on their ability to fix CO2 and the overall production costs (Figure 3). Early assessments using stoichiometric metabolic modeling have indicated that while current microbial processes may not yet be competitive with traditional methods, optimized parameters could make them economically interesting alternatives (Liebal et al., 2018). The development of high-activity enzymes and efficient bioreactor designs are crucial for achieving sustainable and cost-effective acetic acid production from CO2. By leveraging genetic modifications, process optimizations, and innovative reactor designs, these case studies highlight the potential of microbial CO2 fixation and conversion into valuable organic acids, paving the way for sustainable industrial applications. Figure 3 Pathways of carbon fixation to succinate investigated in this study for their economic potential (Adopted from Liebal et al., 2018) Image caption: The reductive pentose phosphate pathway (green), DHAP pathway of methylotrophic yeasts (blue), reductive acetyl-CoA pathway (C. ljungdahlii, yellow), glyoxylate shunt (E. coli, orange), and CETCH pathway (purple). Ac, acetate; AcCoA, acetyl-CoA; AcrCoA, acrylyl-CoA; CH3-THF, methyltetrahydrofolate; CroCoA, crotonyl-CoA; DHAP, dihydroxyacetone phosphate; EthMalCoA, ethylmalonyl-CoA; E4P, erythrose-4-phosphate; Fum, fumarate; F6P, fructose-6-phosphate; GAP, glyceraldehyde-3; Glyox, glyoxylate; Icit, isocitrate; Mal, malate; MeMalCoA, methylmalyl-CoA; MeManlCoA, methylmalonyl-CoA; OAA, oxaloacetate; OGA, 2-oxoglutarate; PEP, phosphoenol pyruvate; PropCoA, propionyl-CoA; Pyr, Pyruvate; RuBP, ribulose-bisphosphate; Ru5P, ribulose-5-phosphat; R5P, ribose-5-phosphate; Suc, succinate; SucCoA, succinyl-CoA; S7P, sedoheptulose-7-phosphate; X5P, xylulose-5-phosphate; 3PG, 3-phosphoglycerate; 4HBut, 4-hydroxyburyrate (Adopted from Liebal et al., 2018)
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