The myxobacteria are single cell bacteria that display a remarkable cooperative multicellular behavior during their life cycle(1). Myxobacteria are gram-negative and move by gliding and form diffusive spreading colonies or so-called "swarms"(2,3). Their cells are appear in two basic shapes : either slender with tapering ends, or cylindrical with blunt, rounded ends(4). They form characteristic fruiting bodies and microcysts under certain conditions. Starvation initiates a sequence of developmental stages culminating after several hours in the formation of multicellular fruiting body. Shortly before the nascent fruiting body aggregates start forming the surface of the colony often displays an elaborate pattern of propagating waves, called 'ripples'(5,6). These waves reflect the local bacterial density, with dense crests appearing much darker than the more sparsely populated troughs(7,8).
In general, the isolation of myxobacteria of all types can be a time-consuming and often tedious process. They are usually obtained from herbivore dung, decaying plant material and bark of living and dead trees by placing samples of these materials in a moist chamber and observing them frequently for the development of characteristic fruiting bodies(9).
The number of strain named to date is small compared to other bacteria.
Therefore, fundamental studies of the myxobacteria are rather limited in certain species, and are restricted to morphology.
In 1892 Thaxter reported on the morphology and classification of the myxobacteria(10). MCCURDY(11-15) group paid attention to the isolation and classification of this group of bacteria, and proposed a classification system based on the morphology of fruiting bodies and microcysts. MASUDA(16) published morphological study of fruiting bodies of a myxobacterium, and Abe et al.(17) reported isolation and purification methods and described their properties. However, little is known about the ecology of myxobacteria, and information about their physiology, biochemistry, chemotaxonomy, and phylogeny is limited. The practical importance of myxobacteria has not been fully determined. However, recent studies have shown this group of microorganisms to be useful sources for producing secondary metabolites(18,19).
Myxobacteria are prolific producers of a variety of bioactive secondary metabolites including antibacterial, antifungal, antiviral and antitumor compounds. Remarkably, Reichenbach found that 60-80% of the myxobacteria tested had antibacterial or antifungal activity(9).
The isolation methods we have used are the placing soil on bacterial smears, the filter paper method, and the agar medium method. Placing soil on bacterial smears was easy to manage.
In the course of a screening for biologically active metabolites from myxobacteria, Chondromyces apiculatus strain JW480 was found to produce apicularen A and cyclo-leucylproryl(20). These compounds were finally purified by diode array detected HPLC. The structure of these compounds were elucidated by spectroscopic analyses.
Apicularen A demonstrated potent cytotoxicity against cultivated human cells. A cometabolite of apicularen A, the cyclo-leucylproryl was not cytotoxic, and showed weak antioxidant activity. None of the tested bacteria and yeast were inhibited.
Apicularen A is a novel macrolide with a unique unsaturated amide side chain(21). Apicularen A shows a remarkable structural similarity to Salicylihalamide A , a compound isolated from marine sponge Haliclona sp., but has much less cytotoxicity. There is also a structural relationship to the Lobatamides A and B, novel cytotoxic macrolides, isolated from the tunicate Aplidium lobatum(22).