Rearrangement in the regulation of sigD gene expression promotes 4-hydroxyisoleucine production in Corynebacterium glutamicum

Corynebacterium glutamicum is widely used in the production of amino acids. C. glutamicum possesses seven sigma factors, among which SigD is responsible for the transcription of genes involved in the synthesis of mycolic acid (MA) and its derivatives, the unique cell envelope of C. glutamicum. To understand the influence of MA synthesis on amino acid production and membrane phenotype of C. glutamicum, the expression of sigD gene and some mycolyltransferase genes, i.e., cmt1, cop1 and cmt2, were regulated by several growth-regulated promoters in this study. Except for 2 mutant strains of P_cg3096-sigD and P_cg1633-cop1, the growth and 4-hydroxyisoleucine (4-HIL) titer of most modified strains did not change significantly. But the 4-HIL titer of P_odhI-sigD strain increased by 20.73% (142.45 ± 3.69 mM) compared to that of control strain (117.99 ± 0.34 mM). After it was cultivated in bioreactor, 4-HIL titer reached 372.56 mM. This may be caused by the increase of MA content, and 17% decrease of cell hydrophobicity and 12% increase of membrane permeability were observed at the exponential phase. In conclusion, we proved that rearrangements in regulation of sigD expression contributed to the improved fermentation performance of C. glutamicum and promoted 4-HIL production.