China
Africa
Explore chapters and articles related to this topic
Fermentative Production of Vitamin B6
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2020
Jonathan Rosenberg, Björn Richts, Fabian M. Commichau
B. subtilis has also been engineered for the conversion of 4-hydroxy-L-threonine (4HT) to the B6 vitamer PN (Commichau et al., 2015). The conversion of 4HT to PN by B. subtilis required the genomic adaptation of the bacteria because like 4HTP also 4HT interferes with threonine and isoleucine biosynthesis (Westley et al., 1971; Katz et al., 1974; Drewke et al., 1993; Kim et al., 2010; Commichau et al., 2014; Rosenberg et al., 2016). The evolved B. subtilis strains had acquired mutations in (1) branched chain amino acid transporters that probably reduce uptake rate of 4HT from the medium and (2) the Phom promoter, resulting in the de-regulation of threonine biosynthesis, thus endogenous resistance to 4HT (Commichau et al., 2015; Rosenberg et al., 2016). The evolved bacteria expressing the native thrB gene, which encodes the promiscuous homoserine kinase ThrB that converts 4HT to 4HTP (Fig. 1.2), and the E. coli pdxA and S. meliloti pdxJ genes produced 65 mg/L PN from 120 mg/L 4HT (Commichau et al., 2015). Surprisingly, although 4HT was completely consumed by the engineered bacteria they did not fully convert it to PN. This observation suggests that unknown host metabolic pathways compete with the heterologous pathway for 4HT.
Host-Vector Systems for Amino Acid-Producing Coryneform Bacteria
Published in Yoshikatsu Murooka, Tadayuki Imanaka, Recombinant Microbes for Industrial and Agricultural Applications, 2020
There are two ways to proceed: one is to gather all of the genes of interest on the same vector; another is to employ several kinds of compatible vectors. A good example of the former strategy is the construction of a composite plasmid by gathering five independently existing chromosomal genes for tryptophan biosynthesis in Saccharomyces cerevisiae [34]. An example of the latter, is our work on the genes for threonine biosynthesis [35]. To construct recombinant threonine-producing B. lactofermentum, we used two compatible plasmid vectors, the derivatives of pHM1519 and pAM330, to clone, respectively, the homoserine dehydrogenase (HD) and homoserine kinase (HK) genes. Both enzymes react at the limiting steps in threonine biosynthesis by B. lactofermentum, and the recombinant strain harboring both hybrid plasmids produced much more of this amino acid than the strain with only one hybrid plasmid (Fig. 3).
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
So far, there have been different metabolic pathways described for PHA synthesis, while the pathways involved in PHA synthesis from glycerol have not been discussed in much detail. The glycerol-based pathways are summarized in Figure 9.3, including the tricarboxylic acid (TCA) cycle, P(3HB) synthesis, fatty acid de novo synthesis, β-oxidation, and the hydroxypropionate synthesis pathway [12,43]. PHA biosynthesis begins with the metabolism of glycerol to form dihydroxyacetone phosphate (DHAP) and 3-hydroxypropionaldehyde [28]. Then, the first molecule, DHAP, is converted into acetyl-CoA through glycolysis. Acetyl-CoA is a vital molecule in PHA synthesis that leads to the formation of the molecule 3-hydroxyalkanoyl-CoA, either hydroxyacyl-CoA (HA-CoA) or hydroxybutyryl-CoA (HB-CoA), of different lengths after going through several reactions in the PHA biosynthesis pathway. Thus, polymerization of these molecules results in the biosynthesis of PHA molecules of different chain lengths. Schematic representation of various pathways involved in PHA synthesis from glycerol [46,50,129]. Note: Enzymes involved in the biosynthesis are: 1. DhaD, Glycerol dehydrogenase; 2. DhaK, Dihydroxyacetone kinase; 3. GlpK, Glycerol kinase; 4. G3P dehydrogenase; 5. Coenzyme A; 6. SucD, Succinyl semialdehyde dehydrogenase; 7. 4hbD, 4-hydroxybutyrate dehydrogenase; 8. 4-hydroxybutyrate-CoA: CoA transferase (OrfZ); 9. PhaC, PHA synthase; 10. PhaA, β- ketothiolase; 11. PhaB, NADP dependent acetoacetyl-CoA reductase; 12. Acyl CoA Dehydrogenase; 13. FadB, S-3-hydroxyacyl-CoA reductase, YdiO, enoyl-CoA reductase; 14. FadB, hydroxyacyl-CoA dehydrogenase/enoyl-CoA hydratase; 15. Yqef/FadA, thiolase; 16. ACC, acyl CoA Carboxylase; 17. FabD, Malonyl transacylase; 18. β-ketoacyl ACP synthase; 19. β-ketoacyl ACP reductase; 20. β-hydroxyacyl ACP dehydrase; 21. enoyl ACP reductase; 22. PhaG, 3-hydroxyacyl-acyl carrier protein CoA transferase; 23. PhaC1 (STQK), PHA synthase; 24. Malonyl CoA reductase, mcr; 25. DhaB, Glycerol dehydratase; 26. AldD, aldehyde dehydrogenase; 27. PCS’, Propanoyl CoA synthatase; 28. PduP, Propionaldehyde dehydrogenase; 29. ThrA, aspartokinase 1, ThrB, homoserine kinase, ThrC, Threonine synthase; 30. Ilv, threonine deaminase.
Interspecific protoplast fusion of atmospheric and room-temperature plasma mutants of Aspergillus generates an L-asparaginase hyper-producing hybrid with techno-economic benefits
Published in Preparative Biochemistry & Biotechnology, 2023
Atim Asitok, Maurice Ekpenyong, Ernest Akwagiobe, Marcus Asuquo, Anitha Rao, David Ubi, Juliet Iheanacho, Eloghosa Ikharia, Agnes Antai, Joseph Essien, Sylvester Antai
Auxanography is an important requirement for mutant characterization as microorganisms require a large repertoire of nutrients for growth. For improved L-asparaginase synthesis, Asp-C-ARTP most-stable mutant lost ability to synthesize L-isoleucine and L-threonine suggesting that their synthesis may interfere with L-asparaginase biosynthetic pathway. Threonine and isoleucine belong to the aspartate family of amino acids with oxaloacetate as precursor metabolite and are synthesized through a common homoserine branch of the pathway.[37] It is logical to conclude that the mutation that caused overproduction of L-asparaginase in Asp-C-180-K occurred in genes thrB and thrC which specify the enzymes homoserine kinase and threonine synthetase respectively, that catalyze the two biochemical steps leading from homoserine to L-threonine and ultimately to isoleucine.