Abstract
The marine environment is a rich source of biodiversity, including microorganisms that have proven to be prolific producers of bioactive secondary metabolites. Arctic seas are less explored than warmer, more accessible areas, providing a promising starting point to search for novel bioactive compounds. In the present work, an Arctic marine Pseudomonas sp. belonging to the Pseudomonas (P.) fluorescence group was cultivated in four different media in an attempt to activate biosynthetic pathways leading to the production of antibacterial and anticancer compounds. Culture extracts were pre-fractionated and screened for antibacterial and anticancer activities. One fraction from three of the four growth conditions showed inhibitory activity towards bacteria and cancer cells. The active fractions were dereplicated using molecular networking based on MS/MS fragmentation data, indicating the presence of a cluster of related rhamnolipids. Six compounds were isolated using HPLC and mass-guided fractionation, and by interpreting data from NMR and high-resolution MS/MS analysis; the structures of the compounds were determined to be five mono-rhamnolipids and the lipid moiety of one of the rhamnolipids. Molecular networking proved to be a valuable tool for dereplication of these related compounds, and for the first time, five mono-rhamnolipids from a bacterium within the P. fluorescence group were characterized, including one new mono-rhamnolipid.
Highlights
It is estimated that only a small percentage of the existing marine bacterial diversity has been cultivated to date
The bacterium isolate M10B774 was isolated from an Atlantic halibut in the Norwegian Sea on a medium containing Difco Marine Broth 15 g/L, peptone 5 g/L, 300 mL filtered seawater and 700 mL
This newly isolated Pseudomonas sp. strain strain was was cultured cultured in four different different media, and the culture extracts were subsequently fractionated into six fractions each prior to bioactivity screening
Summary
It is estimated that only a small percentage of the existing marine bacterial diversity has been cultivated to date. There is a strong likelihood to isolate previously uncultured bacterial strains and some of these will produce new secondary metabolites (SMs) [1]. It is likely to find novel SMs from already cultivated bacteria by applying the OSMAC (one strain many compounds) approach [2]. The concept behind this approach is that some metabolic pathways remain silent during standard cultivation conditions and the corresponding SMs are not synthesized. Introducing small changes into the cultivation conditions can activate different metabolic pathways which may lead to the production of numerous SMs from a single strain [2].
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