Secondary Metabolites And Bioactivity Of Three Microorganisms Associated With Ascidians

Ascidians are one of the major marine animals from which many kinds of marine natural products were isolated. By now, over 1000 metabolites have been isolated from ascidians, including alkaloids, cyclic peptides, polyketides,macrocyclic lactone and many other types. Many of them have significant bioactivities, such as antitumor, antibacterial, antiviral activities and so on. Thus,ascidians metabolites has become a hotspot in the field of natural products chemistry.In recent years, direct and indirect evidences show that some of the bioactive compounds isolated from ascidians were not produced by the ascidian themselves,but actually by their symbiotic microorganisms. In this study, the isolation,structural elucidation and bioactivity determination of microorganisms associated with ascidians provid the research foundation for the development of marine microbial resource and the discovery of novel marine natural products.In this study, the actinomycete HQA809 isolated from the ascidian Styela clava,the actinomycete HQA404 isolated from Botryllus schlosseri, and the fungus HQF059 isolated from Ciona intestinalis were selected as the objective strains for the isolation of metabolites. Separation techniques of natural products were applied to isolate compounds from the crude extracts of their fermentation broth. Compound structures were elucidated by comprehensive analysis of 1D and 2D NMR data, and mass spectrometry. The isolated compounds were tested for their antibacterial activity, toxicity against Artemia salina, α-glucosidase inhibitory activity and cytotoxic activity.A total of six compounds were isolated from these three microorganisms associated with ascidians. Two known α-pyrone compounds, elucidated as(2-butyl)-3-ethy-(2-butyl)-3-ethyl-4-hyd-roxy-2-pyrone(1) and 6-isopropyl group-3-ethyl-4-hydroxy-2-pyrone(2), as well as one novel alkaloid(3) were isolated from HQA809. A known phenol derivative 2-(acetylamino)-phenol(4), and a known phenazine alkaloid 1-hydroxy-6-methoxyphenazine-N5, N10-dioxide(5) were isolated from HQA404. Meantime, a known cyclic peptide(6) was isolated from HQF059.Five known compounds above showed some activities. Compound(5) had a moderate antibacterial activities against Vibrio anguillarum and Vibrio parahaemolyticus with MIC values of 50 μmol·L-1 and 25 μmol·L-1 separately.Compound(1),(2) and(4) had strong lethality against Artemia salina with their LC50 as 33.16 μg·mL-1, 14.36 μg·mL-1 and 9.34 μg·mL-1 separately. The combination of compound(1) and(2), as well as compound(4) and(5) showedlower toxicities and lethal rate. While in α-glucosidase activity inhibition model,only compound(5) had a weak activity. Meantime, compound(1),(2),(4),(5) and(6) had no cytotoxic activity when tested independently, but the combination of compound(4) and(5) had a significant cytotoxic activity.Our results suggest that the metabolites of microorganisms associated with ascidians have novel sturctures or good bioactivities and can be potential resource for developing new natural products.