Fatty Acids With Antibacterial Activity From The Cyanobacterium

Journal of Applied Phycology 15: 263–267, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands.

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Fatty acids with antibacterial activity from the cyanobacterium Oscillatoria redekei HUB 051
Sabine Mundt 1,*, Susann Kreitlow 1 and Rolf Jansen 2
Institute of Pharmacy, Department of Pharmaceutical Biology, Ernst-Moritz-Arndt-University, Friedrich-Ludwig-Jahnstr. 17,Greifswald, 17487, Germany; 2Department of Natural Product Chemistry, German Research Centre for Biotechnology, Braunschweig, Germany; *Author for correspondence (e-mail: smundt@uni-greifswald.de)
Received 1 July 2002; accepted in revised form 13 January 2003
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Key words: -dimorphecolic acid, Agar plate diffusion test, Antibacterial activity, Coriolic acid, Cyanobacteria, Hydroxy fatty acids,Limnothrix redekei, Minimal inhibition concentration, Oscillatoria redekei Abstract Bioassay-guided fractionation of the n-hexane extract prepared from the biomass of the cyanobacterium Oscillatoria redekei syn. Limnothrix redekei HUB 051 by silica gel and RP-18 column chromatography followed by HPLC resulted in the isolation of a mixture of two unsaturated hydroxy fatty acids. Their further separationusing normal phase HPLC resulted in the identification of -dimorphecolic acid, a 9-hydroxy-10E, 12Z-octadecadienoic acid (9-HODE) and of coriolic acid, a 13-hydroxy-9Z, 11E-octadecadienoic acid (13-HODE). In agar plate diffusion test these fatty acids inhibited the growth of the Gram-positive bacteria Bacillus subtilis SBUG 14, Micrococcus flavus SBUG 16 and Staphylococcus aureus SBUG 11 and ATCC25923, but no activity was observed against multiresistant Staphylococcus aureus strains. This is the first report about antibacterial activity of these hydroxylated unsaturated fatty acids and about the occurrence of coriolic acid in cyanobacteria. Cyanobacteria (blue-green algae) showing remarkable ecological and morphological diversity, but so far only a very few species are used inbiotechnological processes such as the production of biomass for health food such as Spirulina (Arthrospira) (Belay et al. 1993). Natural products of Nostoc that are effective against secondary fungal infections in AIDS patients have been patented (Potts 2000). However, during the last decade cyanobacteria have increasingly been shown to provide an excellent source of natural metabolites with antibacterial,antiviral, antifungal and cytotoxic/cytostatic activity. According to their chemical structure most of the isolated compounds belong to polyketides, amides, alkaloids, lactones, peptides and lipopeptides (Falch 1996; Kleinkauf and von Döhren 1997; Hooper et al. 1998; Singh et al. 1999). It seems likely that biosynthesis of such active substances often confers an important selective advantage forcyanobacteria in nature. A pronounced reduction of gram-positive bacteria in lakes during the occurrence of cyanobacterial waterblooms was reported by Chrost (1975)) and the production of antibacterial substances may be one reason for this phenomenon. Today infectious diseases are the main cause of death in developing countries and world wide they hold the second position after heart diseases. Becauseof the growing bacterial resistance against commercial standard and reserve antibiotics the search for new active substances with antibacterial activity against hospital-based multiresistant Staphylococcus aureus (MRSA-strains) is of increasing importance (Service 1995). In a screening programme we investigated extracts from cyanobacterial biomass with solvents of different polarity for theirbiological activity in various in- vitro test systems (Kreitlow et al. 1999; Mundt et al. 2001). Tests for antibacterial activity revealed that the n-hexane extract prepared from the biomass of the laboratory-cultivated cyanobacterium Oscillatoria redekei syn. Limnothrix redekei HUB

264 051, isolated from the Müggelsee, a freshwater lake in Germany, was active against different strains of...