Isolation of germicidins and analysis of their biosynthetic pathways in Streptomyces ardesiacus SCSIO LO23, a marine-derived actinomycete from Onchidium sp.

Abstract:

Marine epiphytic actinomycetes are potential sources of natural bioactive products with unique structures. [Objective] To isolate and identify the secondary metabolites of Streptomyces ardesiacus SCSIO LO23 which was derived from marine Onchidium sp. (Mollusca), and analyze their biosynthetic gene clusters and biosynthetic pathways. [Methods] A variety of media were used to optimize the fermentation of the strain. Further large-scale fermentation and extraction were performed to yield the germicidins. The structures of the germicidins were characterized by spectroscopy and single-crystal X-Ray diffraction. The whole genome of the strain was sequenced by Illumina HiSeq. antiSMASH and BLAST were combined for gene function annotation and biosynthetic pathway analysis of germicidins in the strain. The biosynthetic gene was further verified by heterologous expression. [Results] Six germicidins were isolated and identified from the fermentation products of AM3 medium, which were germicidin A (1), germicidin B (2), germicidin D (3), germicidin H (4), isogermicidin A (5), and isogermicidin B (6). Compounds 2 and 6 showed excitatory effect on zebrafish neurobehavior at the concentration of 30 μmol/L. The biosynthetic gene was verified by bioinformatic analysis and heterologous expression, and the biosynthetic pathways of compounds 1-6 were deduced. [Conclusion] The structures, bioactivity, and the biosynthetic genes of germicidins from S.ardesiacus SCSIO LO23 are clarified, which lays a solid foundation for the study of this type of compounds.

Key words:germicidin;biosynthesis;type Ⅲ polyketide synthase;Streptomyces ardesiacus;marine epiphytic actinomycetes