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Interconnection between PHA and Stress Robustness of Bacteria
Published in Martin Koller, The Handbook of Polyhydroxyalkanoates, 2020
Stanislav Obruca, Petr Sedlacek, Iva Pernicova, Adriana Kovalcik, Ivana Novackova, Eva Slaninova, Ivana Marova
The protective effect of PHA granules was also investigated on the PHA depolymerase deletion PhaZ mutant of Azospirillium brasilense that lost the ability to hydrolyze PHA. While wild-type cells depolymerase PHB into d-3-hydroxybutyrate oligomers by PhaZ depolymerase, the d-ß-hydroxybutyrate is oxidized by NAD dependent d-ß-hydroxybutyrate dehydrogenase to acetoacetate. Acetoacetate can be indirectly transferred into acetoacetyl-CoA via acetoacetyl-CoA synthetase or directly using succinyl-CoA as CoA donor via the activity of CoA transferase. Afterwards, activated acetoacetyl-CoA is hydrolyzed into two acetyl-CoA which can be integrated into the Krebs cycle. The results of the viability of wild type and phaZ mutant are also significantly different, as in previous cases with phbC mutant cells. The greatest difference between bacterial strains after 40 s of UV exposure (254 nm) was that 47.8% of wild type cells remained viable compared to 11% of phaZ deletion mutant cells [62].
Metabolic Engineering for Liquid Biofuels Generations from Lignocellulosic Biomass
Published in Arindam Kuila, Sustainable Biofuel and Biomass, 2019
Bioisobutanol is another high value-added liquid biofuel. Bioisobutanol can be a better liquid biofuel than ethanol due to its higher energy density and lower hygroscopicity. Furthermore, the branched-chain structure of isobutanol gives a higher octane number than the isomeric n-butanol. C. cellulolyticum ATCC 35319 has been metabolically engineered to generate isobutanol from cellulose through incorporation of synthetic operon containing following genes such as B. subtilis acetolactate synthase (Bs_alsS), E. coli acetohydroxyacid isomeroreductase, E. coli dihydroxy acid dehydratase (Ec_yqhD), L. lactis ketoacid decarboxylase (Ll_kivD), and E. coli and L. lactis alcohol dehydrogenases (Ec_adh and Ll_adh) under the control of constitutive ferredoxin (Fd) promoter from C. pasteurianum. Metabolically engineered C. cellulolyticum has achieved bioisobutanol titer of 0.66 g/L using cellulose as sole carbon source (Higashide et al., 2011). E. coli ATCC 11303 has been metabolically engineered to produce bioisopropanol directly from cellobiose through the cellobiose catabolism involving beta-glucosidase (Tfu_0937) from Thermobifida fusca YX fused to the anchor protein Blc (Tfu0937/Blc) on the cell surface. Afterwards, a synthetic operon has been incorporated for isopropanol biosynthesis including C. acetobutylicum genes such as thiolase, Acyl-CoA: acetate/3-ketoacid CoA transferase, acetoacetate decarboxylase, and alcohol dehydrogenase (Ca_thlA, Ca_atoDA, Ca_adc, and Ca_adhB-593). Metabolically engineered E. coli strain has achieved bioisopropanol titer of about 4.1 g/L (Soma et al., 2012). To this end, metabolic engineering and synthetic biology approach helps to improve the production of liquid biofuel production from LB through strengthening microbial bug’s biocatalytic efficiencies.
Biological Process for Butanol Production
Published in Jay J. Cheng, Biomass to Renewable Energy Processes, 2017
Maurycy Daroch, Jian-Hang Zhu, Fangxiao Yang
When accumulation of acids in the fermentation medium reaches the pH value of 4.5–5.0 solventogenic Clostridia shift their metabolism from production of acids to assimilation of these acids and their conversion to solvents (Jones and Woods, 1986). The exact conditions triggering the metabolic switch can differ between the strains and other cultivation parameters. The key enzyme for this transition is acetoacetate: acetate/butyrate CoA-transferase (Enzyme 5 in Figure 8.3). When cells enter the solventogenic phase, this enzyme allows assimilation of acetate and butyrate as acetyl- and butyryl-CoA without the need of ATP hydrolysis. These two intermediates will then serve as precursor molecules for ethanol and butanol. Acetoacetate: acetate/butyrate CoA-transferase is capable of utilizing either acetate or butyrate as the CoA acceptor during conversion of acetoacetyl-CoA to acetoacetate. Acetoacetate, one of the products of the CoA transferase action, is irreversibly converted into acetone and CO2 by acetoacetate decarboxylase (Adc Enzyme 6 in Figure 8.3), a reaction required to “pull” the thermodynamically unfavorable butyryl-CoA formation (Jones and Woods, 1986). This reaction is the main driver for re-assimilation of acids and the reactions are directly coupled to one another. Because of this activity, solventogenic Clostridia can reinternalize previously fermented acids without the need for additional ATP consumption. Because of this relationship the two processes (acid uptake and acetone formation) are directly linked to each other and it is not possible to ferment large yields of butanol without the formation of acetone while using naturally occurring solventogenic strains (Jones and Woods, 1986). In C. acetobutilicum acetone is the final product of this reaction; in C. beijerinckii it is further reduced to isopropanol by a specific alcohol dehydrogenase (Jones and Woods, 1986).
Effect of acute ingestion of β-hydroxybutyrate salts on the response to graded exercise in trained cyclists
Published in European Journal of Sport Science, 2018
Mark Evans, Ella Patchett, Rickard Nally, Rachel Kearns, Matthew Larney, Brendan Egan
Ketone bodies [namely β-hydroxybutyrate (βHB) and acetoacetate (AcAc)] are produced in the liver during periods of low glucose availability such as during fasting, starvation, and ketogenic diets (Balasse & Féry, 1989; Laffel, 1999; Robinson & Williamson, 1980). Although principally acting as an alternative fuel source for the brain when glucose concentrations are diminished, ketone bodies are also used by skeletal muscle to provide up to 10% of energy during exercise in the fasted state (Balasse, Fery, & Neef, 1978; Féry & Balasse, 1983; Fery, Franken, Neef, & Balasse, 1974; Wahren, Sato, Ostman, Hagenfeldt, & Felig, 1984). However, the direct contribution to energy provision may be secondary to the potential metabolic action of supplemental ketones. For instance, ketone bodies have wide-ranging metabolic effects on peripheral tissues such as glucose sparing, anti-lipolytic effects, and stimulation of muscle protein synthesis (Maizels, Ruderman, Goodman, & Lau, 1977; Mikkelsen, Seifert, Secher, Grøndal, & van Hall, 2015; Nair, Welle, Halliday, & Campbell, 1988). During moderate intensity exercise, infusion of sodium AcAc after an overnight fast attenuates the rise in plasma lactate (Féry & Balasse, 1988), whereas sodium βHB infusion similarly alters the metabolic response to very intense exercise in rats (Kamysheva & Ostrovskaia, 1980) and ischemic forearm exercise in humans (Lestan, Walden, Schmaltz, Spychala, & Fox, 1994).