Modulation of multiple gene clusters expression by a single PAS-LuxR transcriptional regulator

Abstract

PAS-LuxR transcriptional regulators are highly conserved enzymes governing polyene macrolide antifungal biosynthesis. PteF is one of such regulators, situated in the polyene macrolide filipin gene cluster from Streptomyces avermitilis. Its mutation leads to a drastic filipin production decline, but also to a severe loss of oligomycin production, an ATP-synthase inhibitor of macrolide structure, and a delay in sporulation, thus it has been considered as a transcriptional activator. Transcriptomic analyses were carried out in S. avermitilis {Delta}pteF and its parental strain S. avermitilis NRRL 8165 as control. Both strains were grown in YEME medium without sucrose, and samples were taken in the exponential and stationary growth phases. 257 genes showed altered expression in the PteF-deleted mutant, most of them in the exponential phase of growth. Surprisingly, despite PteF being an activator of filipin biosynthesis, a majority of the genes affected upon mutation showed overexpression thus suggesting a negative modulation of those genes. Genes affected were related to various metabolic processes, including genetic information processing; DNA, energy, carbohydrate, and lipid metabolism; morphological differentiation; and transcriptional regulation; among others, but particularly to secondary metabolite biosynthesis. Notably, ten secondary metabolite gene clusters out of 38 encoded by the genome, some of them encoding cryptic compounds, showed altered expression profiles in the mutant, suggesting a regulatory role for PteF wider than expected. Transcriptomic results were validated by quantitative reverse transcription polymerase chain reaction. These findings provide important clues to understand the intertwined regulatory machinery that modulates antibiotic biosynthesis in Streptomyces.