A Self-Sustained System Spanning the Primary and Secondary Metabolism Stages to Boost the Productivity of Streptomyces .

Streptomyces species possess strong secondary metabolism, the switches of which from the primary metabolism are complex and thus a challenge to holistically optimize their productivities. To avoid the complex switches and to reduce the limitations of different metabolic stages on the synthesis of metabolites, we designed a Streptomyces self-sustained system ( St SS) that contains two functional modules, the primary metabolism module (PM) and the secondary metabolism module (SM). The PM includes endogenous housekeeping sigma factor σ hrdB and σ hrdB -dependent promoters, which are used to express target genes in the primary metabolism phase. SM consists of the expression cassette of σ hrdB under the control of a secondary metabolism promoter, which maintains continuous activity of the σ hrdB -dependent promoters in the secondary metabolism phase. As a proof-of-principle, the St SS was used to boost the production of some non-toxic metabolites, including indigoidine, undecylprodigiosin (UDP), ergothioneine, and avermectin, in Streptomyces . All these metabolites can undergo a continuous production process spanning the primary and secondary metabolism stages instead of being limited to a specific stage. Scale-up of UDP fermentation in a 4 L fermentor indicated that the StSS is a stable and robust system, the titer of which was enhanced to 1.1 g/L, the highest at present. This study demonstrated that the StSS is a simple but powerful strategy to rationally engineer Streptomyces cell factories for the efficient production of non-toxic metabolites via reconstructing the relationships between primary and secondary metabolism.