Activation of a plasmid-situated type III PKS gene cluster by deletion of a wbl gene in deepsea-derived Streptomyces somaliensis SCSIO ZH66

Abstract

Background: Actinomycete genome sequencing has disclosed a large number of cryptic secondary metabolite biosynthetic gene clusters. However, their unavailable or limited expression severely hampered the discovery of bioactive compounds. The whiB-like (wbl) regulatory genes play important roles in morphological differentiation as well as secondary metabolism; and hence the wblA so gene was probed and set as the target to activate cryptic gene clusters in deepsea-derived Streptomyces somaliensis SCSIO ZH66.Results: wblA so from deepsea-derived S. somaliensis SCSIO ZH66 was inactivated, leading to significant changes of secondary metabolites production in the ΔwblA so mutant, from which α-pyrone compound violapyrone B (VLP B) was isolated. Subsequently, the VLP biosynthetic gene cluster was identified and characterized, which consists of a type III polyketide synthase (PKS) gene vioA and a regulatory gene vioB; delightedly, inactivation of vioB led to isolation of another four VLPs analogues, among which one was new and two exhibited improved anti-MRSA (methicillin-resistant Staphylococcus aureus, MRSA) activity than VLP B. Moreover, transcriptional analysis revealed that the expression levels of whi genes (whiD, whiG, whiH and whiI) and wbl genes (wblC, wblE, wblH, wblI and wblK) were repressed by different degrees, suggesting an intertwined regulation mechanism of wblA so in morphological differentiation and secondary metabolism of S. somaliensis SCSIO ZH66.Conclusions: wblA orthologues would be effective targets for activation of cryptic gene clusters in marine-derived Streptomyces strains, notwithstanding the regulation mechanisms might be varied in different strains. Moreover, the availability of the vio gene cluster has enriched the diversity of type III PKSs, providing new opportunities to expand the chemical space of polyketides through biosynthetic engineering.

Extreme environments: microbiology leading to specialized metabolites

“…Five new α‐pyrone derivatives, violapyrone A–C, J and H ( 136 – 140 ), which showed anti‐MRSA activity were isolated from a Streptomyces somaliensis strain isolated from a deep‐sea sediment (Huang et al ). Extensive chemical profiling of the Antarctic deep‐sea fungus Penicillium crustosum PRB‐2 resulted in the identification of penilactones A and B ( 141 , 142 ), two novel polyketides with unusual highly oxygenated structures, along with known phenolic metabolites (Wu et al ).…”

A New Dioic Acid from a wbl Gene Mutant of Deepsea-Derived Streptomyces somaliensis SCSIO ZH66

“…The ΔwblA so mutant of S. somaliensis SCSIO ZH66 was constructed in our previous study [12]. The fermentation broths of the wild-type and the ΔwblA so mutant strains were extracted with EtOAc, respectively, and were subsequently subjected to high-performance liquid chromatography (HPLC) analysis (Figure 2), in which we observed three significantly enhanced peaks ( 1 – 3 ) in the ΔwblA so mutant compared with those in the wild-type strain at wavelengths of 200 nm.…”

“…9492) was isolated from the deep-sea sediment collected at a depth of 3536 m in the South China Sea (120°0.250′ E; 20°22.971′ N) [17]. The ΔwblA so mutant was obtained as described previously [12]. The strains were grown at 30 °C on a MS (mannitol-soy flour) medium for sporulation.…”

“…The antibacterial activity against five multi-drug resistant (MDR) strains ( S. aureus CCARM 3090, E. coli CCARM 1009, E. faecalis CCARM 5172, E. faecium CCARM 5203, and S. typhimurium CCARM 8250) was tested by the radial diffusion assay as previously described [12]. …”

“…In the previous study, we obtained a series of anti-MRSA (methicillin-resistant Staphylococcus aureus ) α-pyrone compounds (violapyrones A–C, H, and J) from the deepsea-derived S. somaliensis SCSIO ZH66 by disruption of the negative global regulatory gene wblA so [12]. In our continuous search for significantly enhanced compounds in the ΔwblA so mutant strain, one new dioic acid ( 1 ) together with two known butenolides ( 2 and 3 ) were isolated (Figure 1).…”