Bioconversion of l-glutamic acid to α-ketoglutaric acid by an immobilized whole-cell biocatalyst expressing l-amino acid deaminase from Proteus mirabilis

• Developed an immobilized whole-cell biocatalytic process for a-KG production from glutamic acid.
• Compared the suitability of E. coli and B. subtilis as potential biocatalysts overexpressing l-AAD.
• The performance of B. subtilis was superior to that of E. coli though both strains were active.
• The highest a-KG yield was 31% using 15.0 g/L glutamic acid and 20 g/L whole-cell B. subtilis.
• Immobilizing whole cells with alginate increased the recyclability by 23.33% per cycle.

The goal of this work was to develop an immobilized whole-cell biocatalytic process for the environment-friendly synthesis of α-ketoglutaric acid (α-KG) from l-glutamic acid. We compared the suitability of Escherichia coli and Bacillus subtilis strains overexpressing Proteus mirabilisl-amino acid deaminase (l-AAD) as potential biocatalysts. Although both recombinant strains were biocatalytically active, the performance of B. subtilis was superior to that of E. coli. With l-glutamic acid as the substrate, α-KG production levels by membranes isolated from B. subtilis and E. coli were 55.3 ± 1.73 and 21.7 ± 0.39 μg/mg protein/min, respectively. The maximal conversion ratio of l-glutamic acid to α-KG was 31% (w/w) under the following optimal conditions: 15 g/L l-glutamic acid, 20 g/L whole-cell biocatalyst, 5 mM MgCl2, 40 °C, pH 8.0, and 24-h incubation. Immobilization of whole cells with alginate increased the recyclability by an average of 23.33% per cycle. This work established an efficient one-step biotransformation process for the production of α-KG using immobilized whole B. subtilis overexpressing P. mirabilisl-AAD. Compared with traditional multistep chemical synthesis, the biocatalytic process described here has the advantage of reducing environmental pollution and thus has great potential for the large-scale production of α-KG.