A NEW ANTIBACTERIAL POLYKETIDE FROM THE MARINE ALGA-DERIVED ENDOPHITIC Streptomyces sundarbansensis WR1L1S8

With the aim of finding novel marine actinobacteria strains able to produce bioactive metabolites, twentytwo algae-derived actinomycetales were isolated in Bejaia coastline, Algeria. The crude EtOAc extract from Streptomyces sp. WR1L1S8, obtained from brown algae Fucus sp. and identified as Streptomyces sundarbansensis by 16S rRNA analysis, showed the most promising inhibition on the growth of a series of Gram positive and Gram negative bacteria. The known phaechromicin B, C and E were isolated, together with the new chiral polyketide 1, bearing an unusual propyl chain. The 2-hydroxy-γ-pyrone form was established based on the comparison of the experimental FT-IR spectrum to the DFT calculated spectra for both the 2-hydroxy-γ-pyrone and 4-hydroxy-α-pyrone forms and to standard compounds. Metabolite 1 stood out as the most active among the products isolated from Streptomyces sp. WR1L1S8, showing a selective activity against the pathogenic methicillin-resistant S. aureus (MRSA), with a MIC value = 6 μΜ. A further study was designed in order to investigate whether culture conditions (media, seawater concentration and pH values), could induce S. sundarbansensis to produce compound 1. It resulted the major metabolite from starch casein agar (SCA) medium in 50% seawater at pH 7. Metabolite profiles obtained under different culture condition were efficiently evaluated through the analysis on the corresponding crude extracts by online HPLC-DAD/ESI-MS technique.