**Tatyana Makarieva \*, Larisa Shubina, Valeria Kurilenko, Marina Isaeva, Nadezhda Chernysheva, Roman Popov, Evgeniya Bystritskaya, Pavel Dmitrenok and Valentin Stonik**

G.B. Elyakov Pacific Institute of Bioorganic Chemistry (PIBOC), Russian Academy of Sciences, Prospect 100 let Vladivostoku, 159, 690022 Vladivostok, Russia; shubina@piboc.dvo.ru (L.S.); valerie@piboc.dvo.ru (V.K.); issaeva@piboc.dvo.ru (M.I.); chernysheva.nadezhda@gmail.com (N.C.); prs\_90@mail.ru (R.P.); belyjane@gmail.com (E.B.); paveldmt@piboc.dvo.ru (P.D.); stonik@piboc.dvo.ru (V.S.) **\*** Correspondence: makarieva@piboc.dvo.ru; Tel.: +7-950-295-66-25

Received: 6 February 2019; Accepted: 2 April 2019; Published: 4 April 2019

**Abstract:** Twenty-three bacterial strains were isolated from the secreted mucus trapping net of the marine polychaete *Chaetopterus variopedatus* (phylum Annelida) and twenty strains were identified using 16S rRNA gene analysis. Strain CB1-14 was recognized as a new species of the genus *Vibrio* using the eight-gene multilocus sequence analysis (MLSA) and genome sequences of nineteen type *Vibrio* strains. This *Vibrio* sp. was cultured, and 6-*epi*-monanchorin (**2**), previously isolated from the polychaete and two sponge species, was found in the cells and culture broth. The presence of the 6-*epi*-monanchorin was confirmed by its isolation followed by 1H NMR and HRESIMS analysis. These results showed the microbial origin of the bicyclic guanidine alkaloid **2** in *C. variopedatus*.

**Keywords:** guanidine alkaloids; 6-*epi*-monanchorin; HRESI MS; 1H NMR spectra; marine bacteria; *Vibrio* sp.; polychaete; *Chaetopterus variopedatus*; 16S rRNA gene analysis; phylogenetic reconstruction
