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

Enhanced triacylglycerol metabolism contributes to the efficient biosynthesis of spinosad in Saccharopolyspora spinosa

Triacylglycerol (TAG) is crucial for antibiotic biosynthesis derived from Streptomyces, as it serves as an important carbon source. In this study, the supplementation of exogenous TAG led to a 3.92-fold augmentation in spinosad production. The impact of exogenous TAG on the metabolic network of Saccharopolyspora spinosa were deeply analyzed through comparative proteomics. To optimize TAG metabolism and enhance spinosad biosynthesis, the lipase-encoding genes lip886 and lip385 were overexpressed or co-expressed. The results shown that the yield of spinosad was increased by 0.8-fold and 0.4-fold when lip886 and lip385 genes were overexpressed, respectively. Synergistic co-expression of these genes resulted in a 2.29-fold increase in the yield of spinosad. Remarkably, the combined overexpression of lip886 and lip385 in the presence of exogenous TAG elevated spinosad yields by 5.5-fold, led to a drastic increase in spinosad production from 0.036 g/L to 0.234 g/L. This study underscores the modification of intracellular concentrations of free fatty acids (FFAs), short-chain acyl-CoAs, ATP, and NADPH as mechanisms by which exogenous TAG modulates spinosad biosynthesis. Overall, the findings validate the enhancement of TAG catabolism as a beneficial strategy for optimizing spinosad production and provide foundational insights for engineering secondary metabolite biosynthesis pathways in another Streptomyces.

Effects of a Pirin-like protein on strain growth and spinosad biosynthesis in Saccharopolyspora spinosa

Pirin family proteins perform a variety of biological functions and widely exist in all living organisms. A few studies have shown that Pirin family proteins may be involved in the biosynthesis of antibiotics in actinomycetes. However, the function of Pirin-like proteins in S. spinosa is still unclear. In this study, the inactivation of the sspirin gene led to serious growth defects and the accumulation of H2O2. Surprisingly, the overexpression and knockout of sspirin slightly accelerated the consumption and utilization of glucose, weakened the TCA cycle, delayed sporulation, and enhanced sporulation in the later stage. In addition, the overexpression of sspirin can enhance the β-oxidation pathway and increase the yield of spinosad by 0.88 times, while the inactivation of sspirin hardly produced spinosad. After adding MnCl2, the spinosad yield of the sspirin overexpression strain was further increased to 2.5 times that of the wild-type strain. This study preliminarily revealed the effects of Pirin-like proteins on the growth development and metabolism of S. spinosa and further expanded knowledge of Pirin-like proteins in actinomycetes. KEY POINTS: • Overexpression of the sspirin gene possibly triggers carbon catabolite repression (CCR) • Overexpression of the sspirin gene can promote the synthesis of spinosad • Knockout of the sspirin gene leads to serious growth and spinosad production defects.

Comparative Proteomics Reveals the Effect of the Transcriptional Regulator Sp13016 on Butenyl-Spinosyn Biosynthesis in Saccharopolyspora pogona

Butenyl-spinosyn is a highly effective and broad-spectrum biopesticide produced by Saccharopolyspora pogona. However, the yield of this compound is difficult to increase because the regulatory mechanism of secondary metabolism is still unknown. Here, the transcriptional regulator Sp13016 was discovered to be highly associated with butenyl-spinosyn synthesis and bacterial growth. Overexpression of sp13016 improved butenyl-spinosyn production to a level that was 2.84-fold that of the original strain, while deletion of sp13016 resulted in a significant decrease in yield and growth inhibition. Comparative proteomics revealed that these phenotypic changes were attributed to the influence of Sp13016 on the central carbon metabolism pathway to regulate the supply of precursors. Our research helps to reveal the regulatory mechanism of butenyl-spinosyn biosynthesis and provides a reference for increasing the yield of natural products of Actinomycetes.

Bacterioferritin: a key iron storage modulator that affects strain growth and butenyl-spinosyn biosynthesis in Saccharopolyspora pogona

Background

Butenyl-spinosyn, produced by Saccharopolyspora pogona, is a promising biopesticide due to excellent insecticidal activity and broad pesticidal spectrum. Bacterioferritin (Bfr, encoded by bfr) regulates the storage and utilization of iron, which is essential for the growth and metabolism of microorganisms. However, the effect of Bfr on the growth and butenyl-spinosyn biosynthesis in S. pogona has not been explored.

Results

Here, we found that the storage of intracellular iron influenced butenyl-spinosyn biosynthesis and the stress resistance of S. pogona, which was regulated by Bfr. The overexpression of bfr increased the production of butenyl-spinosyn by 3.14-fold and enhanced the tolerance of S. pogona to iron toxicity and oxidative damage, while the knockout of bfr had the opposite effects. Based on the quantitative proteomics analysis and experimental verification, the inner mechanism of these phenomena was explored. Overexpression of bfr enhanced the iron storage capacity of the strain, which activated polyketide synthase genes and enhanced the supply of acyl-CoA precursors to improve butenyl-spinosyn biosynthesis. In addition, it induced the oxidative stress response to improve the stress resistance of S. pogona.

Conclusion

Our work reveals the role of Bfr in increasing the yield of butenyl-spinosyn and enhancing the stress resistance of S. pogona, and provides insights into its enhancement on secondary metabolism, which provides a reference for optimizing the production of secondary metabolites in actinomycetes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01651-x.

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.