Identification of butenolide regulatory system controlling secondary metabolism in Streptomyces albus J1074

Abstract

A large majority of genome-encrypted chemical diversity in actinobacteria remains to be discovered, which is related to the low level of secondary metabolism genes expression. Here, we report the application of a reporter-guided screening strategy to activate cryptic polycyclic tetramate macrolactam gene clusters in Streptomyces albus J1074. The analysis of the S. albus transcriptome revealed an overall low level of secondary metabolism genes transcription. Combined with transposon mutagenesis, reporter-guided screening resulted in the selection of two S. albus strains with altered secondary metabolites production. Transposon insertion in the most prominent strain, S. albus ATGSal2P2::TN14, was mapped to the XNR_3174 gene encoding an unclassified transcriptional regulator. The mutant strain was found to produce the avenolide-like compound butenolide 4. The deletion of the gene encoding a putative acyl-CoA oxidase, an orthologue of the Streptomyces avermitilis avenolide biosynthesis enzyme, in the S. albus XNR_3174 mutant caused silencing of secondary metabolism. The homologues of XNR_3174 and the butenolide biosynthesis genes were found in the genomes of multiple Streptomyces species. This result leads us to believe that the discovered regulatory elements comprise a new condition-dependent system that controls secondary metabolism in actinobacteria and can be manipulated to activate cryptic biosynthetic pathways.

Regulation of Antibiotic Production by Signaling Molecules in Streptomyces

“…In a BLAST survey, we found one to three afsAlike genes in each of nine Streptomyces genomes (Niu et al, 2016). In another study, BLAST search for homologs of AfsA from S. griseus within the actinobacteria genomes available from public databases showed that AfsA-like proteins are present in most actinomycetes (Ahmed et al, 2017). The widespread distribution of GBLs was further confirmed by using VB-and IM-2-deficient strains as indicators to examine VB and IM-2 distribution.…”

Butenolides from Streptomyces albus J1074 Act as External Signals To Stimulate Avermectin Production in Streptomyces avermitilis

“…Similar to the case of compound 5, these three butenolides have also been isolated from marine-derived Streptomyces strains (17)(18)(19). In addition, compound 4 was recently identified in a genetically modified S. albus strain (20). However, compounds 2, 3, and 5 have never been isolated from S. albus J1074.…”

“…However, the in vivo function of compounds 2 to 5 in the original producer, S. albus J1074, still remains obscure, because no metabolite changes, other than those of compounds 2 to 5, were observed in the aco disruptant ( Fig. 3), although compound 4 was identified from a disruptant of a putative transcriptional regulatory gene (XNR_3174) and is probably involved in the production of tetramate macrolactams, candicidins, and antimycins A (20). These findings suggest that compound 2 and the other butenolide compounds, 3 to 5, are new members of the butenolide-type Streptomyces hormones and are likely to be "one-way" interspecies signaling molecules from S. albus J1074 to S. avermitilis, unlike in the case of SCB3.…”

“…Recently, Ahmed et al (20) demonstrated that the S. albus aco gene is involved in the biosynthesis of compound 4. On the other hand, we showed that the disruption of the S. albus aco gene abolishes the production of compounds 2 to 5.…”

“…Together with Cyp17, which is involved in generation of the C-10 hydroxy group, the pair of aco and cyp17 genes seems to be an important component for the biosynthesis of avenolide-type compounds. The aco and cyp17 homologs are widely spread throughout the streptomycetes, and they are frequently localized in the same locus (20), suggesting that butenolide-type Streptomyces hormones function as a general class of signaling molecules in regulation of Streptomyces secondary metabolism and also in communicating with each other among different streptomycetes.…”