A novel TetR-type repressor directly modulates precursor supply and utilization for erythromycin biosynthesis

Antibiotic biosynthesis in actinomycetes is controlled by various transcription factors, with TetR family regulators (TFRs) serving as important modulators of this process. We previously discovered a TFR, SACE_1906, which hinders erythromycin yield in <i>Saccharopolyspora erythraea</i>. However, the precise mechanism by which SACE_1906 regulates erythromycin biosynthesis remains elusive. Herein, we confirmed that SACE_1906 directly inhibits the transcription of its own and neighboring alcohol dehydrogenase gene <i>SACE_1905</i>, as well as all genes within the erythromycin biosynthetic cluster. It was found that two identical conserved sites (5'-CACCGGTCGGTATA-3') in the intergenic spacer between <i>SACE_1905</i> and <i>SACE_1906</i> (<i>SACE_1905-1906-int</i>) are necessary for SACE_1906 binding. Deletion of <i>SACE_1906</i> resulted in decreased propionyl-CoA content but increased the intracellular supply of methylmalonyl-CoA. We further proved that SACE_1906 restricts methylmalonyl-CoA production from propionyl-CoA to influence intracellular levels of these two erythromycin biosynthetic precursors through the direct repression of several propionyl-CoA carboxylase genes. Moreover, acetaldehyde has been characterized as an effector molecule of SACE_1906 that weakens its binding affinity for <i>SACE_1905-1906-int</i>. This study reveals a novel mechanism by which SACE_1906 orchestrates erythromycin biosynthesis in response to acetaldehyde, expanding our understanding of small-molecule-mediated regulation for antibiotic biosynthesis in actinomycetes.