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A method has been found for inducing the rapid, quantitative, and relatively synchronous conversion of vegetative rods of a fruiting myxobacterium to microcysts. The conversion is induced by the addition of 0.5M glycerol to a dispersed, growing, liquid culture of Myxococcus xanthus. The vegetative rods are converted to microcysts in about 120 minutes.

A unique selective enrichment procedure has resulted in the isolation and identification of two new genera of marine-derived actinobacteria. Approximately 90% of the microorganisms cultured by using the presented method were from the prospective new genera, a result indicative of its high selectivity. In this study, 102 actinomycetes were isolated from subtidal marine sediments collected from the Bismarck Sea and the Solomon Sea off the coast of Papua New Guinea. A combination of physiological parameters, chemotaxonomic characteristics, distinguishing 16S rRNA gene sequences, and phylogenetic analysis based on 16S rRNA genes provided strong evidence for the two new genera (represented by strains of the PNG1 clade and strain UMM518) within the family Micromonosporaceae. Biological activity testing of fermentation products from the new marine-derived actinomycetes revealed that several had activities against multidrug-resistant grampositive pathogens, malignant cells, and vaccinia virus replication.The order Actinomycetales is composed of approximately 80 genera, nearly all from terrestrial soils, where they live primarily as saprophytes (30,36). All members of the order are characterized in part by their high GϩC DNA content, and most exhibit a highly differentiated developmental life cycle (30). Several recent systematic reevaluations of the order reflected more closely the integration of molecular data (16S rRNA gene sequences). This reorganization resulted in the placement of the two most prolific producers of secondary metabolites, Streptomyces and Micromonospora, in the families Streptomycetaceae and Micromonosporaceae, respectively (30).The diversity of actinomycete secondary metabolites is unrivaled and unmatched in medical significance. Structurally and functionally diverse bioactive compounds have also been isolated from other prokaryotes, including members of the myxobacteria (e.g., Sorangium) and cyanobacteria (e.g., Nostoc), as antibiotics with antimicrobial, antiviral, and antitumor activities (16,21,24,25). Recently, the rate of discovery of new compounds from existing genera obtained from terrestrial sources has decreased, while the rate of reisolation of known compounds has increased. Moreover, the rise in the number of drug-resistant pathogens and the limited success of strategies such as combinatorial chemistry in providing new agents indicate an uncertain forecast for future antimicrobial therapy (17, 18). Thus, it is critical that new groups of microbes from unexplored habitats be pursued as sources of novel antibiotics and other small-molecule therapeutic agents (3).The oceans cover more than 70% of the earth's surface, and little is known about the microbial diversity of marine sediments. As with terrestrial soils, marine sediments contain limited amounts of readily available organic matter, with most sources of carbon being present in complex forms (i.e., cellulose and chitin). However, culture-independent methods have demonstrated that marine sediments contain a wide range of unique microo...

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It is characteristic of myxobacteria to produce large amounts of extracellular material. This report demonstrates that this material in Myxococcus xanthus is fibrillar and describes the structure and chemical composition of the fibrils. The extracellular matrix fibrils are the mediators of cell-cell cohesion in M. xanthus. As such, the fibrils play an important role in the cell-cell interactions that form the basis for the social and developmental lifestyle of this organism. The fibrils are composed of protein and carbohydrate in a 1.0:1.2 ratio. Combined, the two fractions accounted for greater than 85% of the mass of isolated fibrils, and the fibrils were found to compose up to 10% of the dry weight of cells grown at high density on a solid surface. The polysaccharide portion of the fibrils was shown to be composed of five different monosaccharides: galactose, glucosamine, glucose, rhamnose, and xylose. Glucosamine, one of the component monosaccharides of the fibrils and a known morphogen for M. xanthus, inhibited cohesion to a level near that of Congo red (the positive control for cohesion inhibition). Glucose and xylose also inhibited cohesion but less than did glucosamine.Analysis of the morphology of the fibrils, the periodicities within the distribution of fibril diameters observed by field emission scanning electron microscopy, and the observation of fibrils on hydrated cells strongly suggested that the extracellular matrix of M. xanthus was indeed arranged as fibrils. Furthermore, results suggested that the fibrils were constructed as carbohydrate structures with associated proteins.