Bidirectional Regulation of AdpAch in Controlling the Expression of scnRI and scnRII in the Natamycin Biosynthesis of Streptomyces chattanoogensis L10

Abstract

AdpA, an AraC/XylS family protein, had been proved as a key regulator for secondary metabolism and morphological differentiation in <i>Streptomyces griseus</i>. Here, we identify AdpA_ch, an ortholog of AdpA, as a "higher level" pleiotropic regulator of natamycin biosynthesis with bidirectional regulatory ability in <i>Streptomyces chattanoogensis</i> L10. DNase I footprinting revealed six AdpA_ch-binding sites in the <i>scnRI</i>-<i>scnRII</i> intergenic region. Further analysis using the <i>xylE</i> reporter gene fused to the <i>scnRI</i>-<i>scnRII</i> intergenic region of mutated binding sites demonstrated that the expression of <i>scnRI</i> and <i>scnRII</i> was under the control of AdpA_ch. AdpA_ch showed a bi-stable regulatory ability where it firstly binds to the Site C and Site D to activate the transcription of the two pathway-specific genes, <i>scnRI</i> and <i>scnRII</i>, and then binds to other sites where it acts as an inhibitor. When Site A and Site F were mutated <i>in vivo</i>, the production of natamycin was increased by 21% and 25%, respectively. These findings indicated an autoregulatory mechanism where AdpA_ch serves as a master switch with bidirectional regulation for natamycin biosynthesis.