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Biochemical Pathways for the Biofuel Production
Published in Debabrata Das, Jhansi L. Varanasi, Fundamentals of Biofuel Production Processes, 2019
Debabrata Das, Jhansi L. Varanasi
The dark fermentation process, carried out by heterotrophic fermentative bacteria, produces biohydrogen at much higher rates compared to the biophotolysis or photofermentation processes (Manish and Banerjee 2008). Any organic substrates (from simple sugars to complex wastes) can be used for dark-fermentative hydrogen production. It is observed that facultative and obligate anaerobic bacteria can produce hydrogen using different metabolic pathways (Elsharnouby et al. 2013). The facultative anaerobes follow the pyruvate formate lyase (PFL) pathway, while the obligate anaerobes follow the pyruvate ferredoxin oxidoreductase (PFOR) pathway (Figure 4.5). In these pathways, the bacteria use the proton (H+) as the electron acceptor and disposes of the excess electrons in the form of molecular hydrogen (Das and Veziroglu 2008).
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Published in M.R. Riazi, David Chiaramonti, Biofuels Production and Processing Technology, 2017
Nuno Lapa, Elena Surra, Isabel A.A.C. Esteves, Rui P.P.L. Ribeiro, José.P.B. Mota, M.R. Riazi, David Chiaramonti
Glucose is converted into pyruvate through the glycolytic pathway with the regeneration of ATP. Pyruvate degradation may follow two different ways (Rashid et al. 2013): (1) The facultative anaerobic bacteria use the pyruvate formate lyase (PFL) enzyme to produce acetyl coenzyme A (acetyl-CoA) and formate. Formate is then converted into bioH2 with the production of CO2 by formate hydrogen lyase (FHL); (2) The strictly anaerobic bacteria and thermophilic bacteria use the pyruvate ferredoxin oxidoreductase (PFOR) enzyme to convert pyruvate into acetyl-CoA. This intermediate substrate can then be converted into four different alternative final products: butanol and ethanol, acetate with ATP regeneration, or butyrate with bioH2 generation.
Dark Fermentative Hydrogen Production:
Published in Farshad Darvishi Harzevili, Serge Hiligsmann, Microbial Fuels, 2017
Patrícia Madeira da Silva Moura, Joana Resende Ortigueira, Idania Valdez-Vazquez, Ganesh Dattatray Saratale, Rijuta Ganesh Saratale, Carla Alexandra Monteiro da Silva
Hydrogen production via pyruvate formate lyase (Pfl). The formate pathway for H2 production is characteristic of facultative anaerobic enteric bacteria. Hydrogen evolution results from the activity of Pfl and hydrogen formate lyase (Hfl), enzymes that are only expressed under anaerobic conditions. Pfl catalyzes the oxidation of pyruvate to produce acetyl-CoA and formate (Equation 7.6). Hfl, for its part, is a complex of two enzymes, formate dehydrogenase and hydrogenase (Kim and Gadd, 2008). Subsequently, formate dehydrogenase oxidizes formate to CO2, and under fermentative conditions, the electrons are transferred to the hydrogenase that catalyzes proton reduction and generates H2 (Equation 7.7). Hydrogen and carbon dioxide are produced at a 1:1 molar ratio, and this reaction is responsible for a maximum H2 yield of 2 mol/mol in glucose fermentation by Enterobacter aerogenes. Pyruvate+CoA→Acetyl-CoA+FormateFormate→CO2+2H++2e−→CO2+H2
Metabolic engineered E. coli for the production of (R)-1,2-propanediol from biodiesel derived glycerol
Published in Biofuels, 2022
Wilson Sierra, Pilar Menéndez, Sonia Rodríguez Giordano
Surprisingly, a high accumulation of lactate (8) and formate (9) was verified in these trials (Figure S4, SM). These products -in principle unexpected- presented accumulation levels that amounted to 8.8 g.L-1 and 1.4 g.L-1 respectively.The presence of lactic acid (8) can be assigned to methylglyoxal (2) detoxification metabolic routes, such as the S-lactoylglutathione by-pass or the lactaldehyde (3) dismutation pathway [60, 61]. On the other hand, the presence of formic acid (9) would be justified by the action of α-ketobutyrate formate-lyase (encoded by the tdcE gene). This enzyme exhibits pyruvate formate-lyase activity when growing on glucose under anaerobic conditions. Indeed, it has been reported that α-ketobutyrate formate-lyase accepts pyruvate as substrate with the same efficiency as α-ketobutyrate [62–64].
Progress in microbiology for fermentative hydrogen production from organic wastes
Published in Critical Reviews in Environmental Science and Technology, 2019
Equations 1–2 describe the hydrogen production by obligate anaerobes like Clostridium spp. During this process, pyruvate is catalyzed by pyruvate dehydrogenase (PDH), releases electrons and forms AcetylCoA. Then, with the function of ferredoxin in reduced form (Fd (red)) and ferredoxin in oxidized form (Fd (ox)), the released electrons are united with H+ forming H2, which is catalyzed by hydrogenase. Then, AcetylCoA formed in the first step is further disintegrated into acetate and ethanol with the function of Alcohol dehydrogenase (ADH) and Acetate Kinase (ACK). Equations 3–4 describe the hydrogen production by facultative anaerobes like Enterobacter spp. During this process, pyruvate is catalyzed by Pyruvate formate-lyase (PFL), leading to the formation of formate and AcetylCoA. Then, formate is decomposed into H2 and CO2 with the function of Formate hydrogen lyase (FHL) and Hydrogenase. It can be seen that 2 mol H2 can be obtained from 1 mol pyruvate through Equations 1–2, while 1 mol H2 is formed through Equations 3–4. It is obvious that higher hydrogen yield can be obtained by obligate anaerobes than facultative anaerobes, indicating that different microbial distribution can lead to diverse hydrogen production efficiency. Studies have shown maximum hydrogen yield of 3.47 mol H2/mol hexose was obtained by genus Clostridium while no more than 2.6 mol H2/mol hexose was achieved by genus Enterobacter and Bacillus (Harun et al., 2012; Junghare, Subudhi, & Lal, 2012; Beckers, Hiligsmann, Lambert, Heinrichs, & Thonart, 2013; Sinha & Pandey, 2014; Ortigueira et al., 2015).
Energy balance of hydrogen production from wastes of biodiesel production
Published in Biofuels, 2018
Vinayak Laxman Pachapur, Saurabh Jyoti Sarma, Satinder Kaur Brar, Yann Le Bihan, Gerardo Buelna, Mausam Verma
Hydrogen production using dark fermentation involves three types of biochemical reactions. The first reaction is typically found in Escherichia coli and Enterobacteriaceae, where pyruvate is spilt into acetyl-CoA and formate by pyruvate formate lyase (PFL) enzyme. Later, in the presence of formate hydrogen lyase (FHL) enzyme, formate is broken to molecular hydrogen and carbon dioxide release. A second type of reaction involves Clostridium species, whereby pyruvate oxidation into acetyl-CoA with reduction of ferredoxin (Fd) is carried out by pyruvate ferredoxin oxidoreductase (PFOR). The reduced Fd is oxidized in the presence of Fd-dependent hydrogenase (HydA) to release molecular hydrogen. In the third type of reaction, several thermophilic bacteria and many Clostridium species carry out the reaction by NADH: ferredoxin oxidoreductase (NFOR) and HydA. In this reaction, the NADH reduced oxidized Fd in the presence of NFOR, and the Fd (red) was transferred to molecular hydrogen by HydA.[38] During bioconversion of CG, after 30 h, along with hydrogen production, acids are also generated. The increase in acids level causes reduction in optimal pH, which inhibits microorganisms growth and hydrogen production.[27] Varrone et al. [2] carried out fermentation for six days, only to observe the best results reached during the second day of experiments. The hydrogen production reached a stationery phase at 48 h and later started to decrease with no hydrogen production after 60 h.[33] Markov et al. [25] concluded that hydrogen production in the bioreactor starts after 24 h and reaches the maximum production rate on the second day of operation. In the energy balance calculation, fermentation of 48 h is assumed for the production of hydrogen from crude glycerol. From Table 3, the least and highest energy consumption for the total electricity was seen in vegetable source [27] with 51.14% contribution and animal waste [33] with 98% contribution of total energy input.