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The Sustainable Production of Polyhydroxyalkanoates from Crude Glycerol
Published in Martin Koller, The Handbook of Polyhydroxyalkanoates, 2020
Neha Rani Bhagat, Preeti Kumari, Arup Giri, Geeta Gahlawat
The first pathway for PHA synthesis from glycerol involves the combination of the glycolytic pathway and the TCA cycle. Here, glycerol is broken down into dihydroxyacetone (DHA) and glycerol-3-phosphate (G3P) with the help of the enzymes glycerol dehydrogenase (DhaD) and glycerol kinase (GlpK). These two molecules are then broken down into DHAP by the enzymes dihydroxyacetone kinase (DhaK) and glycerol 3-phosphate dehydrogenase [28]. This DHAP molecule is then converted into pyruvate via the glycolysis pathway. Furthermore, through the pyruvate dehydrogenase reaction, pyruvate is converted into acetyl-CoA in the presence of coenzyme A with the release of a CO2 molecule and reduction of NAD+ into NADH. Acetyl-CoA is the major intermediate molecule that further participates in the TCA cycle to form the next substrate, namely succinyl-CoA. Succinyl-CoA is then converted into succinate semialdehyde by the enzyme succinate semialdehyde dehydrogenase (SucD) [44]. Furthermore, succinate semialdehyde is converted into 4-hydroxybutyrate and 4-hydroxybutyryl-CoA via 4-hydroxybutyrate dehydrogenase (4hbD) and 4-hydroxybutyrate-CoA: CoA transferase (OrfZ) [44,45]. This formation of either HA-CoA or HB-CoA is considered as a major step in PHA synthesis where these end molecules get polymerized into scl-PHA molecules via PHA synthase enzymes.
Effects of glycerol and glucose on docosahexaenoic acid synthesis in Aurantiochyrium limacinum SFD-1502 by transcriptome analysis
Published in Preparative Biochemistry & Biotechnology, 2023
Huaqiu Zhang, Xiangying Zhao, Chen Zhao, Jiaxiang Zhang, Yang Liu, Mingjing Yao, Jianjun Liu
Based on the above results, it can be seen that the carbon source utilization rate, biomass and lipid yield of A. limacinum SFD-1502 in 84 hr are better than that of glycerol when glucose is the sole carbon source. When glycerol was used as fermentation substrate, the biomass and lipid yield of A. limacinum SFD-1502 increased continuously in the whole fermentation period. However, there was no significant difference in the lipid production per cell of A. limacinum SFD-1502 lipid created by glycerol and glucose at the end of the fermentation period. This indicates that glucose might be a suitable carbon source for the lag phase and log phase of Aurantiochytrium. This may be due to higher rates of growth and respiration obtained by glucose than with any other substrate.[34] The primary metabolic pathways of glycerol, such as GK and 3-phosphate glycerol dehydrogenase, have weak activity, which inhibit glycerol metabolism.[35,36] However, in order to investigate the effects of glucose and glycerol on the DHA synthesis of Aurantiochytrium, it is necessary to further determine the proportion of DHA in total lipids.
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
The natural production of 1,2-propanediol (4) by E. coli as a glycerol (1) fermentation product has been recently reported, contrary to what was formerly described [28, 42, 43]. Metabolic engineering of this strain, including the overexpression of E. coli methylglyoxal synthase (mgsA), glycerol dehydrogenase (gldA) and an aldehyde reductase (yqhD) resulted in improved 1,2-propanediol (4) yields. Furthermore, the substitution of the native phosphoenol pyruvate dependant dihydroxyacetone kinase (dhaK) for an ATP dependant kinase from C. freundii relieved the identified bottleneck for production of this compound. The above mentioned genetic modifications, along with the knockout of essential enzymes from the competing lactate (8) and acetate (10) fermentation pathways, yielded a strain capable of producing 5.6 g.L-1 de 1,2-propanediol (4) with a yield of 21.3 % (g/g) [39]. The stereochemistry of the isolated diol was not reported.
Cloning and expression of α-amylase in E. coli: genesis of a superior biocatalyst for substrate-specific MFC
Published in International Journal of Green Energy, 2019
Arpita Nandy, Samir Jana, Moumita Khamrai, Vikash Kumar, Shritama Mukherjee, Arindam Bhattacharyya, Patit P. Kundu
More in-depth researches are conducted to develop microbial strains which are able to regenerate mediator/enzyme in its medium for better performance, by ruling out the need of external mediator along with minimizing internal resistance of the cells (Szczupak et al, 2012); Fishilevich et al, 2009); Xiang et al. 2009). Although well-known electroactive strains like Shewanella oneidensis MR-1 or Geobacter sulfurreducens PCA genomes have been sequenced completely and there are possibilities to improve their performance further, the high number of proteins involved in their anaerobic respiration makes functional studies very complicated (Rosenbaum et al, 2010). The proposed electron transfer mechanisms are not completely proven as deletion mutations do not necessarily lead to complete loss of functions as other cytochromes take over and complete the reaction (Rosenbaum and Angenent 2010). The use of a “neutral“ strain that does not have the ability to extracellularly transfer electrons makes the understanding easier of how a genetic alteration can affect the performance of the particular strain. E.coli is a widely studied strain for genetic engineering, and there are plenty of well-practiced protocols for manipulating and screening the strain (Rosenbaum and Angenent 2010). An engineered E. coli over-expressing glycerol dehydrogenase (GldA) served as superior biocatalysts in comparison to native E. coli as reported by Xiang et al. (2009). The enzymatic products functioning as water-soluble redox molecules contributed to the results significantly. In another study by Fishilevich et al. in 2009, glucose oxidase (GOx) enzyme has been displayed on the surface of Saccharomyces cerevisiae to form a self-generating efficient system capable of oxidizing glucose by eliminating the electron transfer barrier (Fishilevich et al, 2012). In the context of this study, a hybrid biocathode has been constructed, displaying two different enzymes on yeast surface on both anode and cathode (Fishilevich et al. 2009). Yeast cells displaying GOx on anode and bilirubin oxidase on the cathode have been reported as a regenerating system, containing a genetically modified organism in both compartments. Though the approaches for improving the performance of fuel cell by engineering microbes in molecular level are limited, it is a novel and progressive way for achieving superior biocatalyst for MFC.