Wenzhi Song

Advisor: Dr. Monica Chander

Biology Department


Identifying the Physiological Activator of SoxR in Streptomyces coelicolor

The Streptomyces coelicolor bacterium produces several secondary metabolites, including actinorhodin (Act), a blue-pigmented redox-active antibiotic. Previous work in the lab has shown that the redox-sensing transcription factor SoxR regulates gene expression when the bacterium is producing Act, which suggests that Act or a redox-active precursor of Act is the physiological activator of SoxR. SoxR-regulated genes include an ABC transporter and several enzymes that are homologous to Act-biosynthetic enzymes. Interestingly, a SoxR null mutant overproduces Act. Based on these observations, we propose that SoxR senses an intermediate in the Act pathway and turns on an Act-detoxification mechanism whereby harmful redox-active pathway intermediates are processed and exported.

This project aims to determine the Act-intermediate that SoxR senses in S. coelicolor. One potential candidate is the quinone, dihydrokalafungin (DHK), which is produced from oxygenation of 6-deoxy-dihydrokalafungin (DDHK) by the enzymes ActVA-ORF5 and ActVA-ORF6. Our strategy is to delete the genes encoding these two enzymes to prevent the formation of DHK. If DHK is the physiological activator of SoxR, then we should expect to see no SoxR-regulated gene expression in this mutant background (SoxR regulon expression will be monitored via quantitative real-time PCR). If, however, we do observe SoxR regulon expression in this background, this would indicate that SoxR senses a downstream intermediate in the Act pathway.