Metabolic engineering of rational screened Saccharopolyspora spinosa for the enhancement of spinosyns A and D production

Increasing the heterologous production of spinosad in Streptomyces albus J1074 by regulating biosynthesis of its polyketide skeleton

Spinosyns are natural broad-spectrum biological insecticides with a double glycosylated polyketide structure that are produced by aerobic fermentation of the actinomycete, Saccharopolyspora spinosa. However, their large-scale overproduction is hindered by poorly understood bottlenecks in optimizing the original strain, and poor adaptability of the heterologous strain to the production of spinosyn. In this study, we genetically engineered heterologous spinosyn-producer Streptomyces albus J1074 and optimized the fermentation to improve the production of spinosad (spinosyn A and spinosyn D) based on our previous work. We systematically investigated the result of overexpressing polyketide synthase genes (spnA, B, C, D, E) using a constitutive promoter on the spinosad titer in S. albus J1074. The supply of polyketide synthase precursors was then increased to further improve spinosad production. Finally, increasing or replacing the carbon source of the culture medium resulted in a final spinosad titer of ∼70 mg/L, which is the highest titer of spinosad achieved in heterologous Streptomyces species. This research provides useful strategies for efficient heterologous production of natural products.

RNA-Seq-Based Transcriptomic Analysis of Saccharopolyspora spinosa Revealed the Critical Function of PEP Phosphonomutase in the Replenishment Pathway

Spinosyns, the secondary metabolites produced by Saccharopolyspora spinosa, are the active ingredients in a family of novel biological insecticides. Although the complete genome sequence of S. spinosa has been published, the transcriptome of S. spinosa remains poorly characterized. In this study, high-throughput RNA sequencing (RNA-seq) technology was applied to dissect the transcriptome of S. spinosa. Through transcriptomic analysis of different periods of S. spinosa growth, we found large numbers of differentially expressed genes and classified them according to their different functions. Based on the RNA-seq data, the CRISPR-Cas9 method was used to knock out the PEP phosphonomutase gene (orf 06952-4171). The yield of spinosyns A and D in S. spinosa-ΔPEP was 178.91 mg/L and 42.72 mg/L, which was 2.14-fold and 1.76-fold higher than that in the wild type (83.51 and 24.34 mg/L), respectively. The analysis of the mutant strains also verified the validity of the transcriptome data. The deletion of the PEP phosphonomutase gene leads to an increase in pyruvate content and affects the biosynthesis of spinosad. The replenishment of phosphoenol pyruvate in S. spinosa provides the substrate for the production of spinosad. We envision that these transcriptomic analysis results will contribute to the further study of secondary metabolites in actinomycetes.

Effect of the TetR family transcriptional regulator Sp1418 on the global metabolic network of Saccharopolyspora pogona

Background

Saccharopolyspora pogona is a prominent industrial strain due to its production of butenyl-spinosyn, a high-quality insecticide against a broad spectrum of insect pests. TetR family proteins are diverse in a tremendous number of microorganisms and some are been researched to have a key role in metabolic regulation. However, specific functions of TetR family proteins in S. pogona are yet to characterize.

Results

In the present study, the overexpression of the tetR-like gene sp1418 in S. pogona resulted in marked effects on vegetative growth, sporulation, butenyl-spinosyn biosynthesis, and oxidative stress. By using qRT-PCR analysis, mass spectrometry, enzyme activity detection, and sp1418 knockout verification, we showed that most of these effects could be attributed to the overexpression of Sp1418, which modulated enzymes related to the primary metabolism, oxidative stress and secondary metabolism, and thereby resulted in distinct growth characteristics and an unbalanced supply of precursor monomers for butenyl-spinosyn biosynthesis.

Conclusion

This study revealed the function of Sp1418 and enhanced the understanding of the metabolic network in S. pogona, and provided insights into the improvement of secondary metabolite production.

Improvement of Spinosad Production upon Utilization of Oils and Manipulation of β-Oxidation in a High-Producing Saccharopolyspora spinosa Strain

Spinosad, a member of polyketide-derived macrolides produced in the actinomycete Saccharopolyspora spinosa, has been developed as a broad-spectrum and effective insecticide. The β-oxidation pathway could be an important source of building blocks for the biosynthesis of spinosad, thus the effect of vegetable oils on the production of spinosad in a high-yield strain was investigated. The spinosad production increased significantly with the addition of strawberry seed oil (511.64 mg/L) and camellia oil (520.07 mg/L) compared to the control group without oil (285.76 mg/L) and soybean oil group (398.11 mg/L). It also revealed that the addition of oils would affect the expression of genes involved in fatty acid metabolism, precursor supply, and oxidative stress. The genetically engineered strain, in which fadD1 and fadE genes of Streptomyces coelicolor were inserted, produced spinosad up to 784.72 mg/L in the medium containing camellia oil, while a higher spinosad production level (843.40 mg/L) was detected with the addition of 0.01 mM of thiourea.

Heterologous Expression of Spinosyn Biosynthetic Gene Cluster in Species Is Dependent on the Expression of Rhamnose Biosynthesis Genes

Spinosyns are a group of macrolide insecticides produced by <i>Saccharopolyspora spinosa</i>. Although <i>S. spinosa</i> can be used for industrial-scale production of spinosyns, this might suffer from several limitations, mainly related to its long growth cycle, low fermentation biomass, and inefficient utilization of starch. It is crucial to generate a robust strain for further spinosyn production and the development of spinosyn derivatives. A BAC vector, containing the whole biosynthetic gene cluster for spinosyn (74 kb) and the elements required for conjugal transfer and site-specific integration, was introduced into different <i>Streptomyces</i> hosts in order to obtain heterologous spinosyn-producing strains. The exconjugants of different <i>Streptomyces</i> strains did not show spinosyn production unless the rhamnose biosynthesis genes from <i>S. spinosa</i> genomic DNA were present and expressed under the control of a strong constitutive <i>ermE</i>*<i>p</i> promoter. Using this heterologous expression system resulted in yields of 1 μg/mL and 1.5 μg/mL spinosyns in <i>Streptomyces coelicolor</i> and <i>Streptomyces lividans</i>, respectively. This report demonstrates spinosyn production in 2 <i>Streptomyces</i> strains and stresses the essential role of rhamnose in this process. This work also provides a potential alternative route for producing spinosyn analogs by means of genetic manipulation in the heterologous hosts.

High Level of Spinosad Production in the Heterologous Host Saccharopolyspora erythraea

Spinosad, a highly effective insecticide, has an excellent environmental and mammalian toxicological profile. Global market demand for spinosad is huge and growing. However, after much effort, there has been almost no improvement in the spinosad yield from the original producer, Saccharopolyspora spinosa Here, we report the heterologous expression of spinosad using Saccharopolyspora erythraea as a host. The native erythromycin polyketide synthase (PKS) genes in S. erythraea were replaced by the assembled spinosad gene cluster through iterative recombination. The production of spinosad could be detected in the recombinant strains containing the whole biosynthesis gene cluster. Both metabolic engineering and UV mutagenesis were applied to further improve the yield of spinosad. The final strain, AT-ES04PS-3007, which could produce spinosad with a titer of 830 mg/liter, has significant potential in industrial applications.

IMPORTANCE

This work provides an innovative and promising way to improve the industrial production of spinosad. At the same time, it also describes a successful method of heterologous expression for target metabolites of interest by replacing large gene clusters.

A New Medium for Improving Spinosad Production by Saccharopolyspora spinosa

BACKGROUND

Spinosad (a mixture of spinosyns A and D) is a unique natural pesticide produced by Saccharopolyspora spinosa. With regard to attempts to improve S. spinosa by classical mutagenesis, we propose that the bottleneck of screening out high-spinosad-production strains is probably caused by the fermentation media.

OBJECTIVES

The current study aimed to identify a new medium to extensively investigate the potential of S. spinosa strains to produce spinosad.

MATERIALS AND METHODS

Statistical and regressive modeling methods were used to investigate the effects of the carbon source and to optimize the production media.

RESULTS

The spinosad production of S. spinosa Co121 increased 77.13%, from 310.44 ± 21.84 μg/mL in the initial fermentation medium (with glucose as the main carbon source) to 549.89 ± 38.59 μg/mL in a new optimized fermentation medium (98.0 g of mannitol, 43.0 g of cottonseed flour, 12.9 g of corn steep liquor, 0.5 g of KH2PO4, and 3.0 g of CaCO3 in 1 L of H2O; pH was adjusted to 7.0 before autoclaving). After screening 4,000 strains, an overall 3.33-fold increase was observed in spinosad titers, starting from the parental strain Co121 in the original fermentation medium and ending with the mutant strain J78 (1035 ± 34 μg/mL) in the optimized medium.

CONCLUSIONS

The optimized fermentation medium developed in this study can probably be used to improve spinosad production in screening industrial strains of S. spinosa.