Abstract

Streptomyces coelicolor M145 (SC) is a model strain characterised by its highly active oxidative metabolism. This results in high levels of oxidative stress and the production of actinorhodin (ACT), a blue polyketide pigment with antioxidant properties. To determine whether oxidative stress triggers ACT biosynthesis in SC, we assessed the effect of adding five nitro-flavone (NF) derivatives to the growth medium. As NF molecules are well-known antioxidants, we hypothesized that their presence in the medium would moderate ACT production. The antioxidant efficiency of NF derivatives depends on their ability to donate electrons. This ability is linked to the nature of their 4’-substituent. The Quantitative Structure–Activity Relationship (QSAR) approach and Hammett constants predict the following order: OH > OCH3 > F > H > NO2. The results obtained demonstrate a clear dose–response relationship between the reduction in ACT production by SC and the antioxidant efficiency of these molecules. Therefore, these results strongly suggest that oxidative stress plays a pivotal role in initiating ACT biosynthesis. Furthermore, these results suggest that the direct spectrophotometric assay of ACT production by SC is a rapid, reliable, and inexpensive method of evaluating the in vivo antioxidant activity of any molecule, as predicted by the QSAR approach.

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