Study on Aerobic Biosynthesis of 4-hydroxybutyric Acid by Escherichia coli Cells upon Heterologous Expression of the 2-ketoglutarate Decarboxylase Gene

The Mycobacterium tuberculosis Rv1248c (kgd) gene has been expressed in the recombinant Escherichia coli strain with the inactivated pathways of mixed-acid fermentation and anaerobic generation of acetyl-CoA, and also with modified system of glucose transport and phosphorylation, and altered regulation of ydfG gene encoding NADPH-dependent dehydrogenase of hydroxy carboxylic acids. It was found that with the intensive 2-ketoglutarate formation during aerobic glucose utilization, 4-hydroxybutyrate synthesis could be resulted not only from the direct conversion of 2-ketoglutarate to succinate semialdehyde by the heterologous enzymatic activity, but also from the involvement of respective tricarboxylic acid cycle intermediate in a cascade of native biochemical reactions. Induced expression of the 2-ketoglutarate decarboxylase gene in the recombinant strain provided an efficient conversion of 2-ketoglutarate to succinate semialdehyde derivatives, while the concentration of synthesized 4-hydroxybutyric acid reached 0.3 mM and has apparently been limited by the activity of the enzyme responsible for the terminal stage of precursor reduction.