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Iso‐maleimycin, a previously unknown constitutional isomer of the antibiotic maleimycin, has been detected in an extract of Streptomyces sp. QL37. Chemical synthesis of both maleimycin (20 % yield over seven steps) and iso‐maleimycin, (15 % yield over six steps) allowed access to reference materials for identification. Gas Chromatography coupled Mass Spectrometry (GC‐MS) analysis demonstrated that of the two isomers, only iso‐maleimycin was present in the extract. This finding supports our hypothesis that iso‐maleimycin is a biosynthetic intermediate of lugdunomycin. Iso‐maleimycin displays low antibiotic activity, with a Minimum Inhibitory Concentration (MIC) value on both E. coli and B. subtilis of 250 µg/mL. [ABSTRACT FROM AUTHOR]

Actinobacteria are a rich source of bioactive molecules, and genome sequencing has shown that the vast majority of their biosynthetic potential has yet to be explored. However, many of their biosynthetic gene clusters (BGCs) are poorly expressed in the laboratory, which prevents discovery of their cognate natural products. To exploit their full biosynthetic potential, better understanding of the signals that promote the expression of BGCs is needed. Here, we show that the human stress hormone epinephrine (adrenaline) elicits siderophore production by Actinobacteria. Catechol was established as the likely eliciting moiety, since similar responses were seen for catechol and for the catechol-containing molecules dopamine and catechin but not for related molecules. Exploration of the catechol-responsive strain Streptomyces sp. MBT84 using mass spectral networking revealed elicitation of a BGC that produces the angucycline glycosides aquayamycin, urdamycinone B and galtamycin C. Heterologous expression of the catechol-cleaving enzymes catechol 1,2-dioxygenase or catechol 2,3-dioxygenase counteracted the eliciting effect of catechol. Thus, our work identifies the ubiquitous catechol moiety as a novel elicitor of the expression of BGCs for specialized metabolites. The biosynthetic gene clusters of Actinobacteria are poorly expressed in the laboratory, necessitating a better understanding of the signals that promote their expression in order to exploit their full biosynthetic potential. Here, the authors show that the stress hormone epinephrine elicits the expression of biosynthetic gene clusters and influences the metabolism of Streptomyces, with the catechol moiety proving key to this response. [ABSTRACT FROM AUTHOR]