Unique secondary metabolites of a Streptomyces strain isolated from extreme salty wetland show antioxidant and antibacterial activities

Aims: To identify and assess the biological activities of the crude extract of a Streptomyces isolate from a salty wetland, an extreme environment likely to induce secondary metabolism of micro-organisms.

Methods and results: The crude extract from the isolate Streptomyces lanatus strain AR2 displayed antibacterial activity against Gram-positive bacteria (MICs ranging from 5 to 50 μg ml^-1 ) and antioxidant activity as revealed in DPPH (2,2-diphenyl-1-picrylhydrazyl) assay (IC₅₀ of 0·74 mg ml^-1 ), ferric reducing antioxidant power (IC₅₀ of 1·12 mg ml^-1 ) and metal-chelating power (IC₅₀ of 1·84 mg ml^-1 ) assays. Accordingly, the extract attenuated the H₂ O₂ -induced oxidative stress in the eukaryotic cell model Saccharomyces cerevisiae, assessed by flow cytometry. The profiling of secondary metabolites by HPLC-PDA-ESI-MS/MS revealed the presence of 17 compounds, some of which reported in Streptomyces for the first time to the best of our knowledge: genistein-7-O-glucuronide, naringenin-7-O-rutinoside and resveratrol.

Conclusions: Streptomyces lanatus AR2 produced unique polyketides and phenolic compounds with noticeable bioactivities, allowing adaptation to the extreme environment.

Significance and impact of the study: Sabkhat Seijoumi salty wetland represents a potential niche for Streptomyces yielding useful natural products for biotechnological, pharmaceutical and medical applications.