Four-stage dissolved oxygen strategy based on multi-scale analysis for improving spinosad yield by Saccharopolyspora spinosa ATCC49460

A New Method of Preparing Aurone by Marine Actinomycetes and Its Potential Application in Agricultural Fungicides

A strain of marine actinomycetes was isolated from an intertidal zone and identified as Streptomyces cinereoruber. Through the fermentation of this strain, a compound with fungicidal activity was extracted and purified. Using mass spectrometry (MS) and nuclear magnetic resonance (NMR) data, the metabolite was determined to be an aurone. The toxicity of the aurone toward four kinds of tumor cells-SH-SY5Y, HepG2, A549, and HeLa cells-was verified by the MTT method, delivering IC₅₀ values of 41.81, 47.19, 63.95, and 51.92 μg/mL, respectively. Greenhouse bioassay showed that the aurone exhibited a high fungicidal activity against powder mildew (Botrytis cinerea), cucurbits powder mildew (Sphaerotheca fuliginea (Schlecht ex Ff.) Poll), and rice blast (Pyricularia oryzae).

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.

Comparative transcriptomic analysis of two Saccharopolyspora spinosa strains reveals the relationships between primary metabolism and spinosad production

Saccharopolyspora spinosa is a well-known actinomycete for producing the secondary metabolites, spinosad, which is a potent insecticides possessing both efficiency and safety. In the previous researches, great efforts, including physical mutagenesis, fermentation optimization, genetic manipulation and other methods, have been employed to increase the yield of spinosad to hundreds of folds from the low-yield strain. However, the metabolic network in S. spinosa still remained un-revealed. In this study, two S. spinosa strains with different spinosad production capability were fermented and sampled at three fermentation periods. Then the total RNA of these samples was isolated and sequenced to construct the transcriptome libraries. Through transcriptomic analysis, large numbers of differentially expressed genes were identified and classified according to their different functions. According to the results, spnI and spnP were suggested as the bottleneck during spinosad biosynthesis. Primary metabolic pathways such as carbon metabolic pathways exhibited close relationship with spinosad formation, as pyruvate and phosphoenolpyruvic acid were suggested to accumulate in spinosad high-yield strain during fermentation. The addition of soybean oil in the fermentation medium activated the lipid metabolism pathway, enhancing spinosad production. Glutamic acid and aspartic acid were suggested to be the most important amino acids and might participate in spinosad biosynthesis.

Effect of dissolved oxygen on L-methionine production from glycerol by Escherichia coli W3110BL using metabolic flux analysis method

L-Methionine is an essential amino acid in humans, which plays an important role in the synthesis of some important amino acids and proteins. In this work, metabolic flux of batch fermentation of L-methionine with recombinant Escherichia coli W3110BL was analyzed using the flux balance analysis method, which estimated the intracellular flux distributions under different dissolved oxygen conditions. The results revealed the producing L-methionine flux of 4.8 mmol/(g cell·h) [based on the glycerol uptake flux of 100 mmol/(g cell·h)] was obtained at 30% dissolved oxygen level which was higher than that of other dissolved oxygen levels. The carbon fluxes for synthesizing L-methionine were mainly obtained from the pathway of phosphoenolpyruvate to oxaloacetic acid [15.6 mmol/(g cell·h)] but not from the TCA cycle. Hence, increasing the flow from phosphoenolpyruvate to oxaloacetic acid by enhancing the enzyme activity of phosphoenolpyruvate carboxylase might be conducive to the production of L-methionine. Additionally, pentose phosphate pathway could provide a large amount of reducing power NADPH for the synthesis of amino acids and the flux could increase from 41 mmol/(g cell·h) to 51 mmol/(g cell·h) when changing the dissolved oxygen levels, thus meeting the requirement of NADPH for L-methionine production and biomass synthesis. Therefore, the following modification of the strains should based on the improvement of the key pathway and the NAD(P)/NAD(P)H metabolism.

Enhanced production of pleuromutilin by Pleurotus mutilus and study on its molecular structure

This study aims to enhance the accumulation of pleuromutilin by Pleurotus mutilus and to analyze the molecular structure of pleuromutilin. The results showed that a novel three-stage DO control strategy (60% DO, 1-3d; 45% DO, 4-6d; 30% DO, 7-9d) was very effective for improving the pleuromutilin accumulation and the highest production reached 12g/L, a 4-fold increase over a constant DO strategy. Furthermore, the flow behavior of fermentation broth appeared Newtonian with a maximum μap of 3.9×10-3Pa·s. Meanwhile the molecular formula (C22H34O5), molecular weight (378.5) and structural formula of pleuromutilin were concluded based on spectroscopy and element assay. The main components were hydroxyl, methyl, methylene, carbonyl, carboxyl, and polycyclic hydrocarbon. This work demonstrated that DO strategy was suitable for scalable production of pleuromutilin, which makes pleuromutilin more affordable as materials in food.

RETRACTED ARTICLE: Comparative analysis of the Corynebacterium glutamicum transcriptome in response to changes in dissolved oxygen levels

The dissolved oxygen (DO) level of a culture of Corynebacterium glutamicum (C. glutamicum) in a bioreactor has a significant impact on the cellular redox potential and the distribution of energy and metabolites. In this study, to gain a deeper understanding of the effects of DO on the metabolism of C. glutamicum, we sought to systematically explore the influence of different DO concentrations on genetic regulation and metabolism through transcriptomic analysis. The results revealed that after 20 h of fermentation, oxygen limitation enhanced the glucose metabolism, pyruvate metabolism and carbon overflow, and restricted NAD+ availability. A high oxygen supply enhanced the TCA cycle and reduced glyoxylate metabolism. Several key genes involved in response of C. glutamicum to different oxygen concentrations were examined, which provided suggestions for target site modifications in developing optimized oxygen supply strategies. These data provided new insights into the relationship between oxygen supply and metabolism of C. glutamicum.

Dissolved oxygen control strategy for improvement of TL1-1 production in submerged fermentation by Daldinia eschscholzii

BACKGROUND

2,3-Dihydro-5-hydroxy-2-methylchromen-4-one (TL1-1) is a phenolic compound with significant anti-fungal and anti-cancer activities produced by Daldinia eschscholzii (D. eschscholzii). However, studies have rarely been reported on the fermentation process of D. eschscholzii due to the urgent demand for its pharmaceutical researches and applications.

RESULTS

In this work, the optimal fermentation medium for improved TL1-1 yield was first obtained in a shake flask. As the fermentation process was scaling up, the marked effects of dissolved oxygen (DO) on cell growth and TL1-1 biosynthesis were observed and confirmed. Controlling a suitable DO level by the adjustment of agitation speed and aeration rate remarkably enhanced TL1-1 production in a lab-scale bioreactor. Moreover, the fermentation of D. eschscholzii was successfully applied in 500-L bioreactor, and TL1-1 production has achieved 873.63 mg/L, approximately 15.4-fold than its initial production (53.27 mg/L).

CONCLUSIONS

Dissolved oxygen control strategy for enhancing TL1-1 production was first proposed. Furthermore, control of the appropriate DO level has successfully performed for improving TL1-1 yield and scale-up of D. eschscholzii fermentation process.

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.

In situ high-valued utilization and transformation of sugars from Dioscorea zingiberensis C.H. Wright for clean production of diosgenin

The industrial production of diosgenin in China generates a large amount of high-sugar wastes with low bioavailability, which causes serious pollution to the environment. In this study, a new clean and efficient process for the production of diosgenin was developed using sugars through in situ high-valued transformation. The sugar mixture from Dioscorea zingiberensis C.H. Wright contained abundant beneficial components. Nine typical microorganisms that produced intracellular products were evaluated. Saccharopolyspora spinosa was selected for recursive protoplast fusion to increase the spinosad yield by 46.3% compared with that of the wildtype. Diosgenin and spinosad co-production was conducted in a 100L bioreactor, with pH controlled by adding glucose. The biological oxygen demand of the effluent water decreased from 15,000mg/L to 450mg/L; hence, the proposed process is environment friendly.