Single cell mutant selection for metabolic engineering of actinomycetes

Combined transcriptomic and pangenomic analyses guide metabolic amelioration to enhance tiancimycins production

Exploration of high-yield mechanism is important for further titer improvement of valuable antibiotics, but how to achieve this goal is challenging. Tiancimycins (TNMs) are anthraquinone-fused enediynes with promising drug development potentials, but their prospective applications are limited by low titers. This work aimed to explore the intrinsic high-yield mechanism in previously obtained TNMs high-producing strain Streptomyces sp. CB03234-S for the further titer amelioration of TNMs. First, the typical ribosomal RpsL(K43N) mutation in CB03234-S was validated to be merely responsible for the streptomycin resistance but not the titer improvement of TNMs. Subsequently, the combined transcriptomic, pan-genomic and KEGG analyses revealed that the significant changes in the carbon and amino acid metabolisms could reinforce the metabolic fluxes of key CoA precursors, and thus prompted the overproduction of TNMs in CB03234-S. Moreover, fatty acid metabolism was considered to exert adverse effects on the biosynthesis of TNMs by shunting and reducing the accumulation of CoA precursors. Therefore, different combinations of relevant genes were respectively overexpressed in CB03234-S to strengthen fatty acid degradation. The resulting mutants all showed the enhanced production of TNMs. Among them, the overexpression of fadD, a key gene responsible for the first step of fatty acid degradation, achieved the highest 21.7 ± 1.1 mg/L TNMs with a 63.2% titer improvement. Our studies suggested that comprehensive bioinformatic analyses are effective to explore metabolic changes and guide rational metabolic reconstitution for further titer improvement of target products. KEY POINTS: • Comprehensive bioinformatic analyses effectively reveal primary metabolic changes. • Primary metabolic changes cause precursor enrichment to enhance TNMs production. • Strengthening of fatty acid degradation further improves the titer of TNMs.

Building a highly efficient Streptomyces super-chassis for secondary metabolite production by reprogramming naturally-evolved multifaceted shifts

Streptomyces has an extensive array of bioactive secondary metabolites (SMs). Nevertheless, devising a framework for the heterologous production of these SMs remains challenging. We here reprogrammed a versatile plug-and-play Streptomyces super-chassis and established a universal pipeline for production of diverse SMs via understanding of the inherent pleiotropic effects of ethanol shock on jadomycin production in Streptomyces venezuelae. We initially identified and characterized a set of multiplex targets (afsQ1, bldD, bldA, and miaA) that contribute to SM (jadomycin) production when subjected to ethanol shock. Subsequently, we developed an ethanol-induced orthogonal amplification system (EOAS), enabling dynamic and precise control over targets. Ultimately, we integrated these multiplex targets into functional units governed by the EOAS, generating a universal and plug-and-play Streptomyces super-chassis. In addition to achieving the unprecedented titer and yield of jadomycin B, we also evidenced the potential of this super-chassis for production of diverse heterologous SMs, including antibiotic oxytetracycline, anticancer drug doxorubicins, agricultural herbicide thaxtomin A, and plant growth regulator guvermectin, all with the yields of >10 mg/g glucose in a simple mineral medium. Given that the production of SMs all required complexed medium and the cognate yields were usually much lower, our achievement of using a universal super-chassis and engineering pipeline in a simple mineral medium is promising for convenient heterologous production of SMs.

Unravelling key enzymatic steps in C-ring cleavage during angucycline biosynthesis

Angucyclines are type II polyketide natural products, often characterized by unusual structural rearrangements through B- or C-ring cleavage of their tetracyclic backbone. While the enzymes involved in B-ring cleavage have been extensively studied, little is known of the enzymes leading to C-ring cleavage. Here, we unravel the function of the oxygenases involved in the biosynthesis of lugdunomycin, a highly rearranged C-ring cleaved angucycline derivative. Targeted deletion of the oxygenase genes, in combination with molecular networking and structural elucidation, showed that LugOI is essential for C12 oxidation and maintaining a keto group at C6 that is reduced by LugOII, resulting in a key intermediate towards C-ring cleavage. An epoxide group is then inserted by LugOIII, and stabilized by the novel enzyme LugOV for the subsequent cleavage. Thus, for the first time we describe the oxidative enzymatic steps that form the basis for a wide range of rearranged angucycline natural products.

Product-driven high-throughput screening of industrial filamentous actinomycetes

Traditional strain breeding of industrial filamentous actinomycetes has long been hampered by insufficient screening throughput. From microtiter plate based methods to droplet-based microfluidic screening, various novel product-driven high-throughput screening (HTS) methods have pushed the screening speed limit towards a minimum of hundreds of strains per second with single cell resolution.

Total Biosynthesis of Mutaxanthene Unveils a Flavoprotein Monooxygenase Catalyzing Xanthene Ring Formation

Flavoprotein monooxygenases (FPMOs) play important roles in generating structural complexity and diversity in natural products biosynthesized by type II polyketide synthases (PKSs). In this study, we used genome mining to discover novel mutaxanthene analogues and investigated the biosynthesis of these aromatic polyketides and their unusual xanthene framework. We determined the complete biosynthetic pathway of mutaxathene through in vivo gene deletion and in vitro biochemical experiments. We show that a multifunctional FPMO, MtxO4, catalyzes ring rearrangement and generates the required xanthene ring through a multistep transformation. In addition, we successfully obtained all necessary enzymes for in vitro reconstitution and completed the total biosynthesis of mutaxanthene in a stepwise manner. Our results revealed the formation of a rare xanthene ring in type II polyketide biosynthesis, and demonstrate the potential of using total biosynthesis for the discovery of natural products synthesized by type II PKSs.