Myxobacrteria are single cell bacteria that display remarkable cooperative multicellular behavior during their life cycle. Myxobacteria are gram-negative and move by gliding and form diffusive spreading colonies or so-called "swarms". Using exoenzymes, they analyse different biological macromolecules as well as whole microorganisms such as bacteria and yeast. These organisms form characteristic fruiting bodies which are not produced by other bacteria.
The search for novel compounds strongly depends upon the availability of novel strains. Especially, myxobacterium Sorangium strains have proved to be extremely versatile producers of biologically active secondary metabolites. However, they are not obtained by routine method for culturing bacteria and thus require a special technique for their isolation and culture.
By using filter paper method and different purification methods, a number of Sorangium strains have been isolated as pure cultures from soil at different regions of Korea. Our collection increased last year by 96 strains. In the course of our screening for bioactive compounds from our culture collection, two Sorangium strains were chosen for isolation of their secondary metabolites on the basis of bioassay-guided fractionation.
An ethyl acetate extract of the culture of Sorangium cellulosum KM1045 showed cytotoxic activity when tested in vitro against human cancer cells. Systematic fractionation of the extract led to isolation and characterization of chivosazole F(1) as a cytotoxic principle. Chivosazole F demonstrated potent cytotoxicity against human cancer cells, having ED50 values ranging from 0.1 to 13.7ng/mL. Against human cancer cells such as SK-OV-3, the activity of chivosazole F was more than 90 times stronger than that of doxorubicin in terms of ED50. It also showed moderate antifungal activity against Candida albicans.
An antifungal activity was detected in the culture broth of S. cellulosum KM1033. Guided by the results of antifungal test, the organic extracts from the culture broth were separated by silica and RP-18 column chromatographies followed by silica HPLC to yield an active compound, as a colorless oil. The 1H NMR spectrum of this compound in comparison with that of coriolide(2) isolated from Monnina emarginata seed oil reported by Phillips, B. E. et al(1970) indicated similar chemical shift, leading to the conclusion that both compounds were identical. As much as 1000μg/mL this compound was found to be active against C. albicans, causing a 26.4mm inhibition zone.