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

Pin Yu,Qing-Ting Bu,Xu-Ming Mao,Yong-Quan Li,Yi-Li Tang

doi:10.3389/fmicb.2018.00316

Abstract

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

Highlights

The secondary metabolic process in Streptomyces is regulated by a complex regulatory network involving pathway-specific, pleiotropic, and global regulators which respond to a variety of physiological and environmental condition alterations (van Wezel and McDowall, 2011; Liu et al, 2013)
Based on our previous study that AdpAch affected the transcription of these two pathway-specific genes (Du et al, 2011a), we speculated that AdpAch may act as a “higher level” pleiotropic regulator for regulating the natamycin biosynthesis
Retardation was readily detected upon the addition of 50 pM AdpAch with the probe RI–RII, while the addition of 50- to 100-fold excess of unlabeled specific PCR product reduced the proportion of the labeled promoter-containing fragment (Figure 1). These data clearly demonstrate that AdpAch could bind to the scnRI–scnRII intergenic region and could control the expression of these two pathway-specific genes

Summary

Introduction

The secondary metabolic process in Streptomyces is regulated by a complex regulatory network involving pathway-specific, pleiotropic, and global regulators which respond to a variety of physiological and environmental condition alterations (van Wezel and McDowall, 2011; Liu et al, 2013). The transcription of adpA in Streptomyces griseus is repressed by ArpA, the receptor protein for A-factor (Onaka and Horinouchi, 1997). When A-factor reaches a critical concentration, it binds to ArpA and confers the conformational change of ArpA (Ohnishi et al, 1999). This results in dissociation of ArpA from the adpA promoter, in turn switching on the expression of adpA (Ohnishi et al, 1999). The induced AdpA activates the transcription of AdpAch Regulates the Transcription of scnRI and scnRII various genes related to secondary metabolism such as strR, the pathway-specific regulatory genes for streptomycin in S. griseus (Retzlaff and Distler, 1995; Tomono et al, 2005)

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Conclusion