A new peucemycin derivative and impacts of peuR and bldA on peucemycin biosynthesis in Streptomyces peucetius

Streptomyces peucetius ATCC 27952 is known to produce a variety of secondary metabolites, including two important antitumor anthracyclines: daunorubicin and doxorubicin. Identification of peucemycin and 25-hydroxy peucemycin (peucemycin A), as well as their biosynthetic pathway, has expanded its biosynthetic potential. In this study, we isolated a new peucemycin derivative and identified it as 19-hydroxy peucemycin (peucemycin B). Its antibacterial activity was lower than those of peucemycin and peucemycin A. On the other hand, this newly identified peucemycin derivative had higher anticancer activity than the other two compounds for MKN45, NCI-H1650, and MDA-MB-231 cancer cell lines with IC50 values of 76.97 µM, 99.68 µM, and 135.2 µM, respectively. Peucemycin biosynthetic gene cluster revealed the presence of a SARP regulator named PeuR whose role was unknown. The presence of the TTA codon in the peuR and the absence of global regulator BldA in S. peucetius reduced its ability to regulate the peucemycin biosynthetic gene cluster. Hence, different mutants harboring these genes were prepared. S. peucetius bldA25 harboring bldA produced 1.75 times and 1.77 times more peucemycin A (11.8 mg/L) and peucemycin B (21.2 mg/L), respectively, than the wild type. On the other hand, S. peucetius R25 harboring peuR produced 1.86 and 1.79 times more peucemycin A (12.5 mg/L) and peucemycin B (21.5 mg/L), respectively, than the wild type. Finally, strain S. peucetius bldAR25 carrying bldA and peuR produced roughly 3.52 and 2.63 times more peucemycin A (23.8 mg/L) and peucemycin B (31.5 mg/L), respectively, than the wild type. KEY POINTS: • This study identifies a new peucemycin derivative, 19-hydroxy peucemycin (peucemycin B). • The SARP regulator (PeuR) acts as a positive regulator of the peucemycin biosynthetic gene cluster. • The overexpression of peuR and heterologous expression of bldA increase the production of peucemycin derivatives.

Manipulation of two regulatory genes for efficient production of chromomycins in Streptomyces reseiscleroticus

Background

Regulatory genes play critical roles in natural product biosynthetic pathways. Chromomycins are promising anticancer natural products from actinomycetes. This study is aimed to create an efficient strain for production of these molecules by manipulating the regulatory genes.

Results

A putative but silent chromomycin biosynthetic gene cluster was discovered in Streptomyces reseiscleroticus. Heterologous expression of the ketosynthase, chain length factor, and acyl carrier protein in Streptomyces lividans confirmed that they are responsible for the assembly of a decaketide. Two regulatory genes are present in this gene cluster, including SARP-type activator SrcmRI and PadR-like repressor SrcmRII. Either overexpression of SrcmRI or disruption of SrcmRII turned on the biosynthetic pathway of chromomycins. The production titers of chromomycin A₃/A₂ in R5 agar in these two strains reached 8.9 ± 1.2/13.2 ± 1.6 and 49.3 ± 4.3/53.3 ± 3.6 mg/L, respectively. An engineered strain was then constructed with both SrcmRII disruption and SrcmRI overexpression, which produced chromomycins A₃ and A₂ in R5 agar at 69.4 ± 7.6 and 81.7 ± 7.2 mg/L, respectively. Optimization of the culture conditions further increased the titers of chromomycins A₃ and A₂ respectively to 145.1 ± 15.3 and 158.3 ± 15.4 mg/L in liquid fermentation.

Conclusions

This work revealed the synergistic effect of manipulation of pathway repressor and activator genes in the engineering of a natural product biosynthetic pathway. The resulting engineered strain showed the highest production titers of chromomycins by a strain of Streptomyces, providing an efficient way to produce these pharmaceutically valuable molecules.

Electronic supplementary material

The online version of this article (10.1186/s13036-018-0103-x) contains supplementary material, which is available to authorized users.