PccD Regulates Branched-Chain Amino Acid Degradation and Exerts a Negative Effect on Erythromycin Production in Saccharopolyspora Erythraea

Branched-chain amino acid (BCAA) degradation is a major source of propionyl coenzyme A (propionyl-CoA), a key precursor of erythromycin biosynthesis in In this study, we found that the operon, responsible for BCAA degradation, was regulated directly by PccD, a transcriptional regulator of propionyl-CoA carboxylase genes. The transcriptional level of the operon was upregulated 5-fold in a gene deletion strain (Δ strain) and decreased 3-fold in a overexpression strain (WT/pIB-), demonstrating that PccD was a negative transcriptional regulator of the operon. The deletion of significantly improved the Δ strain's growth rate, whereas overexpression repressed WT/pIB- growth rate, in basic Evans medium with 30 mM valine as the sole carbon and nitrogen source. The deletion of and the BcdhE1 gene (genes in the operon) resulted in lower growth rates of Δ and ΔBcdhE1 strains, respectively, on 30 mM valine, further suggesting that the operon is involved in BCAA degradation. Both overexpression (WT/pIB-) and inactivation (Δ strain) improve erythromycin production (38% and 64%, respectively), whereas the erythromycin production of strain WT/pIB- was decreased by 48%. Lastly, we explored the applications of engineering and in an industrial high-erythromycin-producing strain. deletion in industrial strain E3 (E3) improved erythromycin production by 20%, and the overexpression of in E3Δ (E3Δ/pIB-) increased erythromycin production by 39% compared with E3 in an industrial fermentation medium. Addition of 30 mM valine to industrial fermentation medium further improved the erythromycin production by 23%, a 72% increase from the initial strain E3. We describe a operon involved in BCAA degradation in The genes of the operon are repressed by a TetR regulator, PccD. The results demonstrated that PccD controlled the supply of precursors for biosynthesis of erythromycin via regulating the BCAA degradation and propionyl-CoA assimilation and exerted a negative effect on erythromycin production. The findings reveal a regulatory mechanism in feeder pathways and provide new strategies for designing metabolic engineering to increase erythromycin yield.