Preliminary study on marine associated bacteria-marine invertebrate relationship: observation of valinomycin from Streptomyces in Stichopus vastus

We isolated valinomycin and its analogs from Streptomyces sp. SV 21 obtained from sea cucumber Stichopus vastus. Besides its antibacterial capacity, past studies on valinomycin also showed a broad-spectrum antiviral activity. From an ecological perspective, valinomycin showed interesting bioactivities in host-microbes relationships, such as protection against pathogenic fungi in leafcutter ant Acromymex echinatior and suppression of large patch disease in zoysia grass Zoysia japonica. However, valinomycin's ecological role remains unclear in the marine environment. For that reason, we observed a trace of valinomycin in S. vastus. We extracted S.vastus with MeOH. Unlike the extract of Streptomyces sp. SV 21, the extract of S. vastus showed no activity when tested against environmental bacteria using disc-diffusion assays. The crude extract was fractionated with n-hexane, DCM, BuOH, and water. The samples were then analyzed with UHPLC-MS. The MS spectra showed valinomycin was not detected in the MeOH extract. However, some mass fragments of valinomycin were observed in the mass spectra of the DCM and BuOH fractions. These results could pave the way for further studies on the observation of valinomycin in the parts of sea cucumber and/or its habitat and valinomycin's role for marine organisms, especially sea cucumbers.