Investigation of Secondary Metabolites of North Sea Bacteria: Fermentation, Isolation, Structure Elucidation and Bioactivity

Abstract

In this work 39 bacterial strains from the North Sea were submitted to the chemical and biological screening and due to the results four strains were examined thoroughly for interesting secondary metabolites. Various biotechnical methods were used to promote the yields of secondary metabolites up to 6 mg/L. This resulted in the chromatographic isolation of tropodithietic acid (11) and other eight new natural products (12, 34, 35, 36, 37, 44, 46, 51). The biological activities of them were tested against bacteria, fungi, different tumour cell lines, saline shrimps, nematode and ion channel. 11 showed inhibition activities in all assays except for the ion channel. In total 24 structures were elucidated with spectroscopic methods and X-ray analysis. In addition one bacterial strain (H260) was cultured with OSMAC method to activate its biosynthetic ability of producing peptides. Four of diketopiperazines (54 - 57) and their isomers were identified with HPLC-ESIMS-MS. The primary assignment of a bioactive peptide has proved the result of the NRPS-screening that this strain contains NRPS.