Abstract
Actinobacteria represent one of the most fertile sources for the discovery and development of natural products (NPs) with medicinal and industrial importance. However, production titers of actinobacterial NPs are usually low and require optimization for compound characterization and/or industrial production. In recent years, a wide variety of novel enabling technologies for engineering actinobacteria have been developed, which have greatly facilitated the optimization of NPs biosynthesis. In this review, we summarize the recent advances of synthetic biology approaches for overproducing desired drugs, as well as for the discovery of novel NPs in actinobacteria, including dynamic metabolic regulation based on metabolite-responsive promoters or biosensors, multi-copy chromosomal integration of target biosynthetic gene clusters (BGCs), promoter engineering-mediated rational BGC refactoring, and construction of genome-minimized Streptomyces hosts. Integrated with metabolic engineering strategies developed previously, these novel enabling technologies promise to facilitate industrial strain improvement process and genome mining studies for years to come.
Highlights
As a kind of Gram-positive bacteria with high GC content, actinobacteria undergo complex morphological differentiation and secondary metabolism processes (Barka et al, 2016)
Streptomyces species are capable of producing a wide range of secondary metabolites, such as polyketides, non-ribosomal peptides and terpenes, and possess the unique metabolic background needed for heterologous expression of natural products (NPs) biosynthetic gene clusters (BGCs) from actinobacteria or other bacteria with high-GC content (Liu et al, 2018; Nepal and Wang, 2019)
We envision that NP discovery and development will be rapidly accelerated by the refactoring and amplification of whole biosynthetic pathways in combination with powerful heterologous expression platforms
Summary
As a kind of Gram-positive bacteria with high GC content, actinobacteria undergo complex morphological differentiation and secondary metabolism processes (Barka et al, 2016). Our group recently developed an advanced MSGE method (aMSGE) based on the “multiple integrases-multiple attB sites” concept (Figure 2B; Li et al, 2019b) In this improved method, native attB sites of different orthogonal SSR systems in the actinomycetal genome are simultaneously applied to multicopy integration of target genes or BGCs, rather than introducing foreign attB sites into the host chromosome. A plug-and-play amplification toolkit was designed and constructed, which contains 27 modular recombination plasmids with single or multiple SSR systems Using this innovative technique, we achieved a high-efficiency introduction of the 5-oxomilbemycin A3/A4 BGC into the parental strain Streptomyces hygroscopicus with up to four extra copies, resulting in a significant increase in the production titers of 5-oxomilbemycin A3/A4 (Li et al, 2019b). The aMSGE method could not be used for BGC amplification in actinobacteria without native attB sites
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