Abstract
Regulators of the WhiB-like (wbl) family are playing important role in the complex regulation of metabolic and morphological differentiation in Streptomyces. In this study, we investigated the role of wblI, a member of this family, in the regulation of secondary metabolite production in Streptomyces lividans. The over-expression of wblI was correlated with an enhanced biosynthesis of undecylprodigiosin and actinorhodin and with a reduction of the biosynthesis of yCPK and of the grey spore pigment encoded by the whiE locus. Five regulatory targets of WblI were identified using in vitro formaldehyde crosslinking and confirmed by EMSA and qRT-PCR. These included the promoter regions of wblI itself, two genes of the ACT cluster (actVA3 and the intergenic region between the divergently orientated genes actII-1 and actII-2) and that of wblA, another member of the Wbl family. Quantitative RT-PCR analysis indicated that the expression of actVA3 encoding a protein of unknown function as well as that of actII-1, a TetR regulator repressing the expression of actII-2, encoding the ACT transporter, were down regulated in the WblI over-expressing strain. Consistently the expression of the transporter actII-2 was up-regulated. The expression of WblA, that is known to have a negative impact on ACT biosynthesis, was strongly down regulated in the WblI over-expressing strain. These data are consistent with the positive impact that WblI over-expression has on ACT biosynthesis. The latter might result from direct activation of ACT biosynthesis and export and from repression of the expression of WblA, a likely indirect, repressor of ACT biosynthesis.
Highlights
Streptomyces are Gram-positive, filamentous soil bacteria of considerable biotechnological importance
We demonstrated that the over-expression of the homologue of WblI in S. lividans TK24, greatly enhanced the weak ability of this strain to synthetize undecylprodigiosin (RED) and actinorhodin (ACT), peptidyl and polyketide secondary metabolites, respectively whereas it had a negative impact on the biosynthesis of yCPK, a type I polyketide as well as of the grey spore polyketide pigment encoded by the whiE locus
The deletion of wblI had little impact on the already weak production of these antibiotics in S. lividans TK24 (Fig 1). These results demonstrated the positive regulatory effect of WblI on ACT and RED biosynthesis in S. lividans TK24
Summary
Streptomyces are Gram-positive, filamentous soil bacteria of considerable biotechnological importance This genus produces two thirds of all known antibiotics as well as other bio-active molecules, including antitumor agents, immune-suppressants, apoptosis inducers and antifungals, herbicides, insecticides etc. The tip ends of the aerial hyphae differentiate into uni-genomic spores and the production of a grey pigment encoded by the whiE locus accompanied the complete differentiation process [2,3]. This complex morphological development is mainly under the control of the bld and whi genes, that are required for the formation of aerial mycelium and spores, respectively [2,3]
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