**1. Introduction**

Various guanidine-containing natural products, isolated from different marine invertebrates, demonstrate antifungal, antibacterial, antiviral, and antitumor properties [1] and are suitable compounds for drug development due to high levels of their bioactivities and water solubility. Moreover, some natural guanidine-containing compounds, such as streptomycin, have already been introduced in the clinic.

Most of the marine guanidine alkaloids found in marine sponges are polycyclic, and two bicyclic representatives of this group, namely monanchorin (**1**) and 6-*epi*-monanchorin (**2**), are known. These compounds were isolated from representatives of two phylogenetically distant taxa, namely marine sponges *Monanchora ungiculata* and *Halichondria panicea* (phylum Porifera) [2,3], and marine polychaete *Chaetopterus variopedatus* (phylum Annelida) [4]. Previously it has been reported that the compound **1** shows weak cytotoxic activity against IC2 murine mast cells [2], while compounds **1** and **2** (Figure 1) are able to inhibit the migration and colony formation of cisplatin-resistant cancer NCCIT-R cells [4].

**Figure 1.** Structures of natural compounds **1** and **2**.

The presence of the alkaloids **1** and **2** in such different taxa could indicate that a common unidentified marine microorganism(s), accumulated in both sponges and the polychaete is a genuine producer of these secondary metabolites of unknown biogenesis. Really, the presence of the same secondary metabolites in distantly related animal taxa sometimes point to potential symbiotic or dietary sources of the corresponding substances. However, experimental evidences of their microbial origin were rarely obtained. Recently, we compared levels of these alkaloid content in different body parts of the polychaete *C. variopedatus* [5,6]. Both alkaloids were predominant into the food net parts of the animals and the content of 6-epi-monanchorin (**2**) was very high (5.0% of dry weight) [4]. These findings prompted us to undertake the present study. We have tried to identify the biogenetic origin of the above mentioned polychaete metabolites.

#### **2. Results and Discussion**

#### *2.1. Isolation of Microorganisms*

The secreted mucous net of the polychaete was pre-rinsed in sterile sea water. Pieces of tissue were aseptically removed and homogenized in sterile sea water. Bacterial strains were isolated by plating samples of tissue homogenates onto medium plates containing the modified MN medium [7]. The plates were incubated aerobically at 20 ◦C for 7 days. The bacterial colonies that grew on the DifcoTMMarine Agar 2216 Becton, Dickinson and Company (BD) with that medium were picked up and classified morphologically and biochemically. Twenty-three bacterial strains were isolated in pure cultures and then analyzed by MALDI MS.
