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

Lukuan Hou,Yanhong Qiu,Wenli Li,Huayue Li,Jianhua Ju,Huiming Huang

doi:10.1186/s12934-016-0515-6

Abstract

BackgroundActinomycete 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 wblAso gene was probed and set as the target to activate cryptic gene clusters in deepsea-derived Streptomyces somaliensis SCSIO ZH66.ResultswblAso from deepsea-derived S. somaliensis SCSIO ZH66 was inactivated, leading to significant changes of secondary metabolites production in the ΔwblAso 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 wblAso in morphological differentiation and secondary metabolism of S. somaliensis SCSIO ZH66.ConclusionswblA 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0515-6) contains supplementary material, which is available to authorized users.

Highlights

Actinomycete genome sequencing has disclosed a large number of cryptic secondary metabolite biosynthetic gene clusters
Inactivation of wblAso led to significant enhancement of violapyrone B (VLP B) production As wblA and its orthologous genes were reported to be down-regulators for secondary metabolism in Streptomyces strains [11, 12, 24, 25], the orthologous gene designated wblAso was probed from S. somaliensis SCSIO ZH66 and was set as a target for activating cryptic gene clusters
Gene inactivation was performed to detect its impact on production of secondary metabolites in S. somaliensis SCSIO ZH66

Summary

Introduction

Actinomycete genome sequencing has disclosed a large number of cryptic secondary metabolite biosynthetic gene clusters. 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 the wblAso gene was probed and set as the target to activate cryptic gene clusters in deepsea-derived Streptomyces somaliensis SCSIO ZH66. The control of antibiotic biosynthesis involves complex regulatory cascades and intertwined networks, and many of them are coordinately regulated together with the morphological differentiation [5, 7]. The whiB-like (wbl) regulatory genes have received much attention due to their diverse biological roles, such as in morphological differentiation and secondary metabolism [8, 9]. WblA and its homologues have been reported to serve as global regulators for the biosynthesis of various antibiotics, mostly in a negative manner (such as for actinorhodin [8], tautomycetin [11] and doxorubicin [12]); it was found to exert dual function in antibiotic biosynthesis in Streptomyces chattanoogensis L10 [13] and Streptomyces ansochromogenes 7100 [14] as well

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