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.

Transcriptional regulators of secondary metabolite biosynthesis in Streptomyces

In the post-genome era, great progress has been made in metabolic engineering using recombinant DNA technology to enhance the production of high-value products by Streptomyces. With the development of microbial genome sequencing techniques and bioinformatic tools, a growing number of secondary metabolite (SM) biosynthetic gene clusters in Streptomyces and their biosynthetic logics have been uncovered and elucidated. In order to increase our knowledge about transcriptional regulators in SM of Streptomyces, this review firstly makes a comprehensive summary of the characterized factors involved in enhancing SM production and awakening SM biosynthesis. Future perspectives on transcriptional regulator engineering for new SM biosynthesis by Streptomyces are also provided.

Characterization and engineering of Streptomyces griseofuscus DSM 40191 as a potential host for heterologous expression of biosynthetic gene clusters

Streptomyces griseofuscus DSM 40191 is a fast growing Streptomyces strain that remains largely underexplored as a heterologous host. Here, we report the genome mining of S. griseofuscus, followed by the detailed exploration of its phenotype, including the production of native secondary metabolites and ability to utilise carbon, nitrogen, sulphur and phosphorus sources. Furthermore, several routes for genetic engineering of S. griseofuscus were explored, including use of GusA-based vectors, CRISPR-Cas9 and CRISPR-cBEST-mediated knockouts. Two out of the three native plasmids were cured using CRISPR-Cas9 technology, leading to the generation of strain S. griseofuscus DEL1. DEL1 was further modified by the full deletion of a pentamycin BGC and an unknown NRPS BGC, leading to the generation of strain DEL2, lacking approx. 500 kbp of the genome, which corresponds to a 5.19% genome reduction. DEL2 can be characterized by faster growth and inability to produce three main native metabolites: lankacidin, lankamycin, pentamycin and their derivatives. To test the ability of DEL2 to heterologously produce secondary metabolites, the actinorhodin BGC was used. We were able to observe a formation of a blue halo, indicating a potential production of actinorhodin by both DEL2 and a wild type.

Manipulating the expression of SARP family regulator BulZ and its target gene product to increase tacrolimus production

Tacrolimus (FK506), an effective immunosuppressant, is widely used in the treatment of autoimmune diseases. In this study, we identified that BulZ, a Streptomyces antibiotic regulatory protein (SARP) family regulator, acted as a positive regulator for spore differentiation and tacrolimus production. A knockout of bulZ resulted in a 47.5% decrease of tacrolimus production and a delay of spore differentiation. Using quantitative real-time PCR (qRT-PCR) analysis and electrophoretic mobility shift assays (EMSAs), it was found that BulZ directly activated the transcriptions of bulZ and bulS2, a putative γ-butyrolactone (GBL) synthetase, and bulS2 was shown to play a positive role in tacrolimus biosynthesis. Meanwhile, BulZ was able to indirectly regulate the transcriptions of the cluster-linked activator genes tcs7 and fkbN, as well as the GBL receptor gene bulR1. STSU_RS22595, which encoded a WhiB family transcriptional regulator, was found to be a previously unknown potential target gene of BulZ based on a whole-genome search of the conserved sequence (5'-TSVAVVVNVNBTSRAGNN-3') of the SARP-binding motifs. Although overexpression of STSU_RS22595 did not result in an obvious enhancement of tacrolimus yield, STSU_RS22595 might have important effects on the spore differentiation process. Finally, co-overexpression of bulZ and its target gene bulS2 improved tacrolimus production by 36% compared to the control strain, reaching 324 mg/L. The insights obtained in this study will help further elucidate the regulatory mechanism of tacrolimus biosynthesis and provide new avenues for further improvement of tacrolimus production.

Four new meridamycin congeners from Streptomyces sp. SR107

Meridamycin and its naturally occurring analog normeridamycin are non-immunosuppressive macrocyclic polyketides with potent neuroprotective activity in dopaminergic neurons.