Efficient conversion of aromatic and phenylpropanoid alcohols to acids by the cascade biocatalysis of alcohol and aldehyde dehydrogenases.

Benzyl and phenylpropanoid acids are widely used in organic synthesis of fine chemicals, such as pharmaceuticals and condiments. However, biocatalysis of these acids has received less attention than chemical synthesis. One of the main challenges for biological production is the limited availability of alcohol dehydrogenases and aldehyde dehydrogenases. Environmental microorganisms are potential sources of these enzymes. In this study, 129 alcohol dehydrogenases and 42 aldehyde dehydrogenases from Corynebacterium glutamicum, Pseudomonas aeruginosa, and Bacillus subtilis were identified and explored with various benzyl and phenylpropanoid alcohol and aldehyde substrates, among which four alcohol dehydrogenases and four aldehyde dehydrogenases with broad substrate specificity and high catalytic activity were obtained. Moreover, a cascade whole-cell catalytic system including ADH-90, ALDH-40, and the NAD(P)H oxidase LreNox was established, which showed high efficiency in converting cinnamyl alcohol and p-methylbenzyl alcohol into the respective carboxylic acids. Remarkably, this biocatalytic system can be easily scaled up to gram-level production, facilitating preparation purposes.

PAS domain containing regulator SLCG_7083 involved in morphological development and glucose utilization in Streptomyces lincolnensis.

BACKGROUND: Streptomyces lincolnensis is well known for producing the clinically important antimicrobial agent lincomycin. The synthetic and regulatory mechanisms on lincomycin biosynthesis have been deeply explored in recent years. However, the regulation involved in primary metabolism have not been fully addressed. RESULTS: SLCG_7083 protein contains a Per-Arnt-Sim (PAS) domain at the N-terminus, whose homologous proteins are highly distributed in Streptomyces. The inactivation of the SLCG_7083 gene indicated that SLCG_7083 promotes glucose utilization, slows mycelial growth and affects sporulation in S. lincolnensis. Comparative transcriptomic analysis further revealed that SLCG_7083 represses eight genes involved in sporulation, cell division and lipid metabolism, and activates two genes involved in carbon metabolism. CONCLUSIONS: SLCG_7083 is a PAS domain-containing regulator on morphological development and glucose utilization in S. lincolnensis. Our results first revealed the regulatory function of SLCG_7083, and shed new light on the transcriptional effects of SLCG_7083-like family proteins in Streptomyces.

Design and deep learning of synthetic B-cell-specific promoters.

Synthetic biology and deep learning synergistically revolutionize our ability for decoding and recoding DNA regulatory grammar. The B-cell-specific transcriptional regulation is intricate, and unlock the potential of B-cell-specific promoters as synthetic elements is important for B-cell engineering. Here, we designed and pooled synthesized 23 640 B-cell-specific promoters that exhibit larger sequence space, B-cell-specific expression, and enable diverse transcriptional patterns in B-cells. By MPRA (Massively parallel reporter assays), we deciphered the sequence features that regulate promoter transcriptional, including motifs and motif syntax (their combination and distance). Finally, we built and trained a deep learning model capable of predicting the transcriptional strength of the immunoglobulin V gene promoter directly from sequence. Prediction of thousands of promoter variants identified in the global human population shows that polymorphisms in promoters influence the transcription of immunoglobulin V genes, which may contribute to individual differences in adaptive humoral immune responses. Our work helps to decipher the transcription mechanism in immunoglobulin genes and offers thousands of non-similar promoters for B-cell engineering.

YLC-assembly: large DNA assembly via yeast life cycle.

As an enabling technique of synthetic biology, the scale of DNA assembly largely determines the scale of genetic manipulation. However, large DNA assembly technologies are generally cumbersome and inefficient. Here, we developed a YLC (yeast life cycle)-assembly method that enables in vivo iterative assembly of large DNA by nesting cell-cell transfer of assembled DNA in the cycle of yeast mating and sporulation. Using this method, we successfully assembled a hundred-kilobase (kb)-sized endogenous yeast DNA and a megabase (Mb)-sized exogenous DNA. For each round, over 104 positive colonies per 107 cells could be obtained, with an accuracy ranging from 67% to 100%. Compared with other Mb-sized DNA assembly methods, this method exhibits a higher success rate with an easy-to-operate workflow that avoid in vitro operations of large DNA. YLC-assembly lowers the technical difficulty of Mb-sized DNA assembly and could be a valuable tool for large-scale genome engineering and synthetic genomics.

Metabolic Engineering for Efficient Production of Z,Z-Farnesol in E. coli.

Z,Z-farnesol (Z,Z-FOH), the all-cis isomer of farnesol, holds enormous potential for application in cosmetics, daily chemicals, and pharmaceuticals. In this study, we aimed to metabolically engineer Escherichia coli to produce Z,Z-FOH. First, we tested five Z,Z-farnesyl diphosphate (Z,Z-FPP) synthases that catalyze neryl diphosphate to form Z,Z-FPP in E. coli. Furthermore, we screened thirteen phosphatases that could facilitate the dephosphorylation of Z,Z-FPP to produce Z,Z-FOH. Finally, through site-directed mutagenesis of cis-prenyltransferase, the optimal mutant strain was able to produce 572.13 mg/L Z,Z-FOH by batch fermentation in a shake flask. This achievement represents the highest reported titer of Z,Z-FOH in microbes to date. Notably, this is the first report on the de novo biosynthesis of Z,Z-FOH in E. coli. This work represents a promising step toward developing synthetic E. coli cell factories for the de novo biosynthesis of Z,Z-FOH and other cis-configuration terpenoids.

Improvement of betanin biosynthesis in Saccharomyces cerevisiae by metabolic engineering.

Betanin is a member of natural pigment betacyanins family and has extensive application in the food industry as an important natural red food colorant. Its relatively inefficient production in nature however hampers access to this phytochemicals through traditional crop-based manufacturing. Microbial bioproduction therefore represents an attractive alternative. Here, we present the construction of a Saccharomyces cerevisiae strain for betanin production. Through minimizing metabolic crosstalk, screening and modifying biosynthetic enzymes, enhancing pathway flux and optimizing fermentation conditions, a final titer of betanin of 28.7 mg/L was achieved from glucose at 25 °C in baffled shake-flask, which is the highest reported titer produced by yeast to our knowledge. This work provides a promising step towards developing synthetic yeast cell factories for de novo biosynthesis of value-added betanin and other betacyanins.

Diversification of phenolic glucosides by two UDP-glucosyltransferases featuring complementary regioselectivity.

BACKGROUND: Glucoside natural products have been showing great medicinal values and potentials. However, the production of glucosides by plant extraction, chemical synthesis, and traditional biotransformation is insufficient to meet the fast-growing pharmaceutical demands. Microbial synthetic biology offers promising strategies for synthesis and diversification of plant glycosides. RESULTS: In this study, the two efficient UDP-glucosyltransferases (UGTs) (UGT85A1 and RrUGT3) of plant origin, that are capable of recognizing phenolic aglycons, are characterized in vitro. The two UGTs show complementary regioselectivity towards the alcoholic and phenolic hydroxyl groups on phenolic substrates. By combining a developed alkylphenol bio-oxidation system and these UGTs, twenty-four phenolic glucosides are enzymatically synthesized from readily accessible alkylphenol substrates. Based on the bio-oxidation and glycosylation systems, a number of microbial cell factories are constructed and applied to biotransformation, giving rise to a variety of plant and plant-like O-glucosides. Remarkably, several unnatural O-glucosides prepared by the two UGTs demonstrate better prolyl endopeptidase inhibitory and/or anti-inflammatory activities than those of the clinically used glucosidic drugs including gastrodin, salidroside and helicid. Furthermore, the two UGTs are also able to catalyze the formation of N- and S-glucosidic bonds to produce N- and S-glucosides. CONCLUSIONS: Two highly efficient UGTs, UGT85A1 and RrUGT3, with distinct regioselectivity were characterized in this study. A group of plant and plant-like glucosides were efficiently synthesized by cell-based biotransformation using a developed alkylphenol bio-oxidation system and these two UGTs. Many of the O-glucosides exhibited better PEP inhibitory or anti-inflammatory activities than plant-origin glucoside drugs, showing significant potentials for new glucosidic drug development.

Modular Engineering of Saccharomyces cerevisiae for De Novo Biosynthesis of Genistein.

Genistein, a nutraceutical isoflavone, has various pharmaceutical and biological activities which benefit human health via soy-containing food intake. This study aimed to construct Saccharomyces cerevisiae to produce genistein from sugar via a modular engineering strategy. In the midstream module, various sources of chalcone synthases and chalcone isomerase-like proteins were tested which enhanced the naringenin production from p-coumaric acid by decreasing the formation of the byproduct. The upstream module was reshaped to enhance the metabolic flux to p-coumaric acid from glucose by overexpressing the genes in the tyrosine biosynthetic pathway and deleting the competing genes. The downstream module was rebuilt to produce genistein from naringenin by pairing various isoflavone synthases and cytochrome P450 reductases. The optimal pair was used for the de novo biosynthesis of genistein with a titer of 31.02 mg/L from sucrose at 25 °C. This is the first report on the de novo biosynthesis of genistein in engineered S. cerevisiae to date. This work shows promising potential for producing flavonoids and isoflavonoids by modular metabolic engineering.

Systems Metabolic Engineering of Escherichia coli Coculture for De Novo Production of Genistein.

Genistein is a plant-derived isoflavone possessing various bioactivities to prevent aging, carcinogenesis, and neurodegenerative and inflammation diseases. As a typical complex flavonoid, its microbial production from sugar remains to be completed. Here, we use systems metabolic engineering stategies to design and develop a three-strain commensalistic Escherichia coli coculture that for the first time realized the de novo production of genistein. First, we reconstituted the naringenin module by screening and incorporating chalcone isomerase-like protein, an auxiliary component to rectify the chalcone synthase promiscuity. Furthermore, we devised and constructed the genistein module by N-terminal modifications of plant P450 enzyme 2-hydroxyisoflavanone synthase and cytochrome P450 enzyme reductase. When naringenin-producing strain was cocultivated with p-coumaric acid-overproducing strain (a phenylalanine-auxotroph), two-strain coculture worked as commensalism through a unidirectional nutrient flow, which favored the efficient production of naringenin with a titer of 206.5 mg/L from glucose. A three-strain commensalistic coculture was subsequently engineered, which produced the highest titer to date of 60.8 mg/L genistein from a glucose and glycerol mixture. The commensalistic coculture is a flexible and versatile platform for the production of flavonoids, indicating a promising future for production of complex natural products in engineered E. coli.

Modular engineering of E. coli coculture for efficient production of resveratrol from glucose and arabinose mixture.

Resveratrol, a valuable plant-derived polyphenolic compound with various bioactivities, has been widely used in nutraceutical industries. Microbial production of resveratrol suffers from metabolic burden and low malonyl-CoA availability, which is a big challenge for synthetic biology. Herein, we took advantage of coculture engineering and divided the biosynthetic pathway of resveratrol into the upstream and downstream strains. By enhancing the supply of malonyl-CoA via CRISPRi system and fine-tuning the expression intensity of the synthetic pathway genes, we significantly improved the resveratrol productivity of the downstream strain. Furthermore, we developed a resveratrol addiction circuit that coupled the growth of the upstream strain and the resveratrol production of the downstream strain. The bidirectional interaction stabilized the coculture system and increased the production of resveratrol by 74%. Moreover, co-utilization of glucose and arabinose by the coculture system maintained the growth advantage of the downstream strain for production of resveratrol throughout the fermentation process. Under optimized conditions, the engineered E. coli coculture system produced 204.80 mg/L of resveratrol, 12.8-fold improvement over monoculture system. This study demonstrates the promising potential of coculture engineering for efficient production of natural products from biomass.

Metabolic Division in an Escherichia coli Coculture System for Efficient Production of Kaempferide.

Kaempferide, a plant-derived natural flavonoid, exhibits excellent pharmacological activities with nutraceutical and medicinal applications in human healthcare. Efficient microbial production of complex flavonoids suffers from metabolic crosstalk and burden, which is a big challenge for synthetic biology. Herein, we identified 4'-O-methyltransferases and divided the artificial biosynthetic pathway of kaempferide into upstream, midstream, and downstream modules. By combining heterologous genes from different sources and fine-tuning the expression, we optimized each module for the production of kaempferide. Furthermore, we designed and evaluated four division patterns of synthetic labor in coculture systems by plug-and-play modularity. The linear division of three modules in a three-strain coculture showed higher productivity of kaempferide than that in two-strain cocultures. The U-shaped division by co-distributing the upstream and downstream modules in one strain led to the best performance of the coculture system, which produced 116.0 ± 3.9 mg/L kaempferide, which was 510, 140, and 50% higher than that produced by the monoculture, two-strain coculture, and three-strain coculture with the linear division, respectively. This is the first report of efficient de novo production of kaempferide in a robust Escherichia coli coculture. The strategy of U-shaped pathway division in the coculture provides a promising way for improving the productivity of valuable and complex natural products.

Combinational quorum sensing devices for dynamic control in cross-feeding cocultivation.

Quorum sensing (QS) offers cell density dependent dynamic regulations in cell culture through devices such as synchronized lysis circuit (SLC) and metabolic toggle switch (MTS). However, there is still a lack of studies on cocultivation with a combination of different QS-based devices. Taking the production of isopropanol and salidroside as case studies, we have mathematically modeled a comprehensive set of QS-regulated cocultivation schemes and constructed experimental combinations of QS devices, respectively, to evaluate their feasibility and optimality for regulating growth competition and corporative production. Glucose split ratio is proposed for the analysis of competition between cell growth and targeted production. Results show that the combination of different QS devices across multiple members offers a new tool with the potential to effectively coordinate synthetic microbial consortia for achieving high product titer in cross-feeding cocultivation. It is also evident that the performance of such systems is significantly affected by dynamic characteristics of chosen QS devices, carbon source control and the operational settings. This study offers insights for future applications of combinational QS devices in synthetic microbial consortia.

Plasticity engineering of plant monoterpene synthases and application for microbial production of monoterpenoids.

Plant monoterpenoids with structural diversities have extensive applications in food, cosmetics, pharmaceuticals, and biofuels. Due to the strong dependence on the geographical locations and seasonal annual growth of plants, agricultural production for monoterpenoids is less effective. Chemical synthesis is also uneconomic because of its high cost and pollution. Recently, emerging synthetic biology enables engineered microbes to possess great potential for the production of plant monoterpenoids. Both acyclic and cyclic monoterpenoids have been synthesized from fermentative sugars through heterologously reconstructing monoterpenoid biosynthetic pathways in microbes. Acting as catalytic templates, plant monoterpene synthases (MTPSs) take elaborate control of the monoterpenoids production. Most plant MTPSs have broad substrate or product properties, and show functional plasticity. Thus, the substrate selectivity, product outcomes, or enzymatic activities can be achieved by the active site mutations and domain swapping of plant MTPSs. This makes plasticity engineering a promising way to engineer MTPSs for efficient production of natural and non-natural monoterpenoids in microbial cell factories. Here, this review summarizes the key advances in plasticity engineering of plant MTPSs, including the fundamental aspects of functional plasticity, the utilization of natural and non-natural substrates, and the outcomes from product isomers to complexity-divergent monoterpenoids. Furthermore, the applications of plasticity engineering for improving monoterpenoids production in microbes are addressed.

Compartmentalized Reconstitution of Post-squalene Pathway for 7-Dehydrocholesterol Overproduction in Saccharomyces cerevisiae.

7-Dehydrocholesterol (7-DHC) is the direct precursor to manufacture vitamin D3. Our previous study has achieved 7-DHC synthesis in Saccharomyces cerevisiae based on the endogenous post-squalene pathway. However, the distribution of post-squalene enzymes between the endoplasmic reticulum (ER) and lipid bodies (LD) might raise difficulties for ERG proteins to catalyze and deliver sterol intermediates, resulting in unbalanced metabolic flow and low product yield. Herein, we intended to rearrange the subcellular location of post-squalene enzymes to alleviate metabolic bottleneck and boost 7-DHC production. After identifying the location of DHCR24 (C-24 reductase, the only heterologous protein for 7-DHC biosynthesis) on ER, all the ER-located enzymes were grouped into four modules: ERG1/11/24, ERG25/26/27, ERG2/3, and DHCR24. These modules attempted to be overexpressed either on ER or on LDs. As a result, expression of LD-targeted DHCR24 and ER-located ERG1/11/24 could promote the conversion efficiency among the sterol intermediates to 7-DHC, while locating module ERG2/3 into LDs improved the whole metabolic flux of the post-squalene pathway. Coexpressing LD-targeted ERG2/3 and DHCR24 (generating strain SyBE_Sc01250035) improved 7-DHC production from 187.7 to 308.2 mg/L at shake-flask level. Further expressing ER-targeted module ERG1/11/24 in strain SyBE_Sc01250035 dramatically reduced squalene accumulation from 620.2 mg/L to the lowest level (by 93.8%) as well as improved 7-DHC production to the highest level (to 342.2 mg/L). Then targeting module ERG25/26/27 to LDs further increased 7-DHC titer to 360.6 mg/L, which is the highest shake-flask level production for 7-DHC ever reported. Our study not only proposes and further proves the concept of pathway compartmentalized reconstitution to regulate metabolic flux but also provides a promising chassis to produce other steroidal compounds through the post-squalene pathway.

Metabolic engineering of Escherichia coli for de novo production of 3-phenylpropanol via retrobiosynthesis approach.

BACKGROUND: 3-Phenylpropanol with a pleasant odor is widely used in foods, beverages and cosmetics as a fragrance ingredient. It also acts as the precursor and reactant in pharmaceutical and chemical industries. Currently, petroleum-based manufacturing processes of 3-phenypropanol is environmentally unfriendly and unsustainable. In this study, we aim to engineer Escherichia coli as microbial cell factory for de novo production of 3-phenypropanol via retrobiosynthesis approach. RESULTS: Aided by in silico retrobiosynthesis analysis, we designed a novel 3-phenylpropanol biosynthetic pathway extending from L-phenylalanine and comprising the phenylalanine ammonia lyase (PAL), enoate reductase (ER), aryl carboxylic acid reductase (CAR) and phosphopantetheinyl transferase (PPTase). We screened the enzymes from plants and microorganisms and reconstructed the artificial pathway for conversion of 3-phenylpropanol from L-phenylalanine. Then we conducted chromosome engineering to increase the supply of precursor L-phenylalanine and combined the upstream L-phenylalanine pathway and downstream 3-phenylpropanol pathway. Finally, we regulated the metabolic pathway strength and optimized fermentation conditions. As a consequence, metabolically engineered E. coli strain produced 847.97 mg/L of 3-phenypropanol at 24 h using glucose-glycerol mixture as co-carbon source. CONCLUSIONS: We successfully developed an artificial 3-phenylpropanol pathway based on retrobiosynthesis approach, and highest titer of 3-phenylpropanol was achieved in E. coli via systems metabolic engineering strategies including enzyme sources variety, chromosome engineering, metabolic strength balancing and fermentation optimization. This work provides an engineered strain with industrial potential for production of 3-phenylpropanol, and the strategies applied here could be practical for bioengineers to design and reconstruct the microbial cell factory for high valuable chemicals.

Combining Metabolic and Monoterpene Synthase Engineering for de Novo Production of Monoterpene Alcohols in Escherichia coli.

The monoterpene alcohols acyclic nerol and bicyclic borneol are widely applied in the food, cosmetic, and pharmaceutical industries. The emerging synthetic biology enables microbial production to be a promising alternative for supplying monoterpene alcohols in an efficient and sustainable approach. In this study, we combined metabolic and plant monoterpene synthase engineering to improve the de novo production of nerol and borneol in prene-overproducing Escherichia coli. We engineered the growth-orthogonal neryl diphosphate (NPP) as the universal precursor of monoterpene alcohol biosynthesis and coexpressed nerol synthase (GmNES) from Glycine max to generate nerol or coexpressed the truncated bornyl diphosphate synthase (LdtBPPS) from Lippia dulcis for borneol production. Further, through site-directed mutation of LdtBPPS based on the structural simulation, we screened multiple variants that markedly elevated the production of acyclic nerol or bicyclic borneol, of which the LdtBPPSS488T mutant outperformed the wild-type LdtBPPS on borneol synthesis and the LdtBPPSF612A variant was superior to GmNES on nerol production. Subsequently, we overexpressed the endogenous Nudix hydrolase NudJ to facilitate the dephosphorylation of precursors and boosted the production of nerol and borneol from glucose. Finally, after the optimization of the fermentation process, the engineered strain ENO2 produced 966.55 mg/L nerol, and strain ENB57 generated 87.20 mg/L borneol in a shake flask, achieving the highest reported titers of nerol and borneol in microbes to date. This work shows a combinatorial engineering strategy for microbial production of natural terpene alcohols.

Integrative Biosynthetic Gene Cluster Mining to Optimize a Metabolic Pathway to Efficiently Produce l-Homophenylalanine in Escherichia coli.

Mining biosynthetic genes for the exploration of hybrid metabolic pathways is a promising approach in heterologous production of natural and unnatural products. Here, we developed an integrative biosynthetic gene cluster (BGC) mining strategy to engineer the biosynthesis of l-homophenylalanine (l-Hph), an important intermediate for the synthesis of angiotensin-converting enzyme inhibitors. We assembled the putative l-Hph BGCs and integrated phylogenetic analysis with target metabolite abundance mapping to prioritize candidate BGCs. To obtain an effective l-Hph pathway, various combinations of candidate genes from different species were screened in an iterative design-build-test stepwise manner. After the pathway was strength balanced and the metabolic flux was enhanced, engineered Escherichia coli produced 1.41 g/L of l-Hph from glucose in feeding shake-flask fermentation. Our cluster mining strategy enabled optimization of the target metabolic pathway, and it would be promising for production of other valuable products in the postgenomic era.

Metabolic Engineering of Escherichia coli for de Novo Production of Betaxanthins.

Betalains are emerging natural pigments with high tinctorial strength and stability, physiological activities, and fluorescent properties for potential application in food, cosmetic, and pharmaceutical industries. Betalains including yellow betaxanthins and red betacyanins are mainly restricted in the Caryophyllales plants. To expand the availability of individual betaxanthins, here, we constructed an Escherichia coli BTA6 for de novo biosynthesis of betalamic acid. Using this strain as a monoculture platform, 14 yellow and 2 red betaxanthins were produced by feeding amino acids and amines. Furthermore, we constructed an l-histidine overproducing strain using chromosome engineering to deattenuate regulation and established a coculture system. After optimization of the initial inoculation ratios and fermentation conditions, the compatible and robust coculture system produced 287.69 mg/L of histidine-betaxanthin. This is the first report on de novo production of betaxanthins in engineered E. coli using glucose as a carbon source. Our work highlights the feasibility of microbial cell factories to produce individual betalains.

Comparative transcriptomic analysis reveals the significant pleiotropic regulatory effects of LmbU on lincomycin biosynthesis.

BACKGROUND: Lincomycin, produced by Streptomyces lincolnensis, is a lincosamide antibiotic and widely used for the treatment of the infective diseases caused by Gram-positive bacteria. The mechanisms of lincomycin biosynthesis have been deeply explored in recent years. However, the regulatory effects of LmbU that is a transcriptional regulator in lincomycin biosynthetic (lmb) gene cluster have not been fully addressed. RESULTS: LmbU was used to search for homologous LmbU (LmbU-like) proteins in the genomes of actinobacteria, and the results showed that LmbU-like proteins are highly distributed regulators in the biosynthetic gene clusters (BGCs) of secondary metabolites or/and out of the BGCs in actinomycetes. The overexpression, inactivation and complementation of the lmbU gene indicated that LmbU positively controls lincomycin biosynthesis in S. lincolnensis. Comparative transcriptomic analysis further revealed that LmbU activates the 28 lmb genes at whole lmb cluster manner. Furthermore, LmbU represses the transcription of the non-lmb gene hpdA in the biosynthesis of L-tyrosine, the precursor of lincomycin. LmbU up-regulates nineteen non-lmb genes, which would be involved in multi-drug flux to self-resistance, nitrate and sugar transmembrane transport and utilization, and redox metabolisms. CONCLUSIONS: LmbU is a significant pleiotropic transcriptional regulator in lincomycin biosynthesis by entirely activating the lmb cluster and regulating the non-lmb genes in Streptomyces lincolnensis. Our results first revealed the pleiotropic regulatory function of LmbU, and shed new light on the transcriptional effects of LmbU-like family proteins on antibiotic biosynthesis in actinomycetes.

Regulatory Patterns of Crp on Monensin Biosynthesis in Streptomyces cinnamonensis.

Monensin, produced by Streptomyces cinnamonensis, is a polyether ionophore antibiotic widely used as a coccidiostat and a growth-promoting agent in agricultural industry. In this study, cyclic AMP receptor protein (Crp), the global transcription factor for regulation of monensin biosynthesis, was deciphered. The overexpression and antisense RNA silencing of crp revealed that Crp plays a positive role in monensin biosynthesis. RNA sequencing analysis indicated that Crp exhibited extensive regulatory effects on genes involved in both primary metabolic pathways and the monensin biosynthetic gene cluster (mon). The primary metabolic genes, including acs, pckA, accB, acdH, atoB, mutB, epi and ccr, which are pivotal in the biosynthesis of monensin precursors malonyl-CoA, methylmalonyl-CoA and ethylmalonyl-CoA, are transcriptionally upregulated by Crp. Furthermore, Crp upregulates the expression of most mon genes, including all PKS genes (monAI to monAVIII), tailoring genes (monBI-monBII-monCI, monD and monAX) and a pathway-specific regulatory gene (monRI). Enhanced precursor supply and the upregulated expression of mon cluser by Crp would allow the higher production of monensin in S. cinnamonensis. This study gives a more comprehensive understanding of the global regulator Crp and extends the knowledge of Crp regulatory mechanism in Streptomyces.