Abstract
Streptomyces sp. GET02.ST and Achromobacter sp. GET02.AC were isolated together from the gut of the wharf roach, Ligia exotica, inhabiting the intertidal zone of the west coast of Korea. The co-cultivation of these two strains significantly induced the production of two new metabolites, ligiamycins A (1) and B (2), which were barely detected in the single culture of Streptomyces sp. GET02.ST. The planar structures of ligiamycins A (1) and B (2) were elucidated as new decalins coupled with amino-maleimides by the analysis of various spectroscopic data, including nuclear magnetic resonance (NMR), ultraviolet (UV), and mass (MS) data. The assignment of two nitrogen atoms in amino-maleimide in 1 was accomplished based on 1H-15N heteroatom single quantum coherence spectroscopy (HSQC) NMR experiments. The relative configurations of the ligiamycins were determined using rotating frame Overhauser effect spectroscopy (ROESY) NMR data, and their absolute configurations were deduced by comparing their experimental and calculated optical rotations. Ligiamycin A (1) displayed antibacterial effects against Staphylococcus aureus and Salmonella enterica, while ligiamycin B (2) exhibited mild cell cytotoxicity against human colorectal cancer cells.
Highlights
Marine microorganisms physically and chemically interact with neighboring microbes. These interactions are regarded as a driving force to produce bioactive secondary metabolites with pharmaceutical potential [1]. Even though mimicking such complex microbial interactions is challenging, co-culturing two microbial strains in a single culture vessel has been continuously utilized to induce the production of previously unreported bioactive natural products, which has contributed to increasing the chemical diversity of marine microbial compounds [2]
The production level was minuscule, and this compound was barely identified by the liquid chromatography (LC)/mass spectrometry (MS) analysis
An additional derivative of 1, ligiamycin B (2), which was hardly detected in the pure cultured medium of GET02.ST, was identified in the LC/MS profile of the co-cultured
Summary
Marine microorganisms physically and chemically interact with neighboring microbes These interactions are regarded as a driving force to produce bioactive secondary metabolites with pharmaceutical potential [1]. From a marine green alga and the marine bacterium Salinispora arenicola [5] These early co-culture experiments among marine microbes did not consider ecological relevance much and randomly mixed two different strains. Recently, it has been realized that co-culturing symbiotic or ecologically relevant microbes more efficiently induces the production of new metabolites that are not produced in single cultures. Among marine invertebrates, which have been considered to harbor microbes potentially producing bioactive metabolites [11], wharf roaches belonging to order Isopoda in the subphylum Crustacea, have not been chemically explored in much detail. We report the isolation, structure determination, and bioactivities of these compounds, ligiamycins A (1) and B (2), from the co-culture of the gut strains of Ligia exotica
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