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There are several instances of cellular differentiation in prokaryotes, including the formation of spores in Bacillus, the fruiting bodies of Myxococcus, and the stalked cells of Caulobacter. The vegetative cells of particular filamentous cyanobacteria can differentiate into three different cell types: N(2)-fixing heterocysts, spore-like akinetes, and motile hormogonia. Heterocysts are crucial for the ability of these photosynthetic bacteria to fix N(2) because they keep the oxygen-labile nitrogenase away from the photosynthetically produced O(2). Heterocysts are morphologically and functionally distinct from vegetative cells in the filament. Their differentiation relies on sophisticated intercellular communication and is tightly regulated. Analyzed by classical mutagenesis for decades, heterocyst differentiation is now being approached by large-scale methodologies, leading to the identification of new elements that might be important in the process.

Bacteria producing secondary metabolites are an important source of natural products with highly diverse structures and biological activities. Developing methods to efficiently mine procaryotic secondary metabolomes for the presence of potentially novel natural products is therefore of considerable interest. Modern mass spectrometry-coupled liquid chromatography can effectively capture microbial metabolic diversity with ever improving sensitivity and accuracy. In addition, computational and statistical tools increasingly enable the targeted analysis and exploration of information-rich LC-MS datasets. In this article, we describe the use of such techniques for the characterization of myxobacterial secondary metabolomes. Using accurate mass data from high-resolution ESI-TOF measurements, target screening has facilitated the rapid identification of known myxobacterial metabolites in extracts from nine Myxococcus species. Furthermore, principal component analysis (PCA), implementing an advanced compound-based bucketing approach, readily revealed the presence of further compounds which contribute to variation among the metabolite profiles under investigation. The generation of molecular formulae for putative novel compounds with high confidence due to evaluation of both exact mass position and isotopic pattern, is exemplified as an important key for de-replication and prioritization of candidates for further characterization.

SummaryIn prokaryotes, the toxin-antitoxin systems are thought to play important roles in growth regulation under stress conditions. In the E. coli MazE-MazF system, MazF toxin functions as an mRNA interferase cleaving mRNAs at ACA sequences to inhibit protein synthesis leading to cell growth arrest. Myxococcus xanthus is a bacterium displaying multicellular fruiting body development during which approximately 80% of cells undergo obligatory cell lysis. Here, we demonstrate that M. xanthus has a solitary mazF gene that lacks a cotranscribed antitoxin gene. The mazF deletion results in elimination of the obligatory cell death during development causing dramatic reduction in spore formation. Surprisingly, MrpC, a key developmental regulator, functions as a MazF antitoxin and a mazF transcription activator. Transcription of mrpC and mazF is negatively regulated via MrpC phosphorylation by a Ser/Thr kinase cascade. These findings reveal the regulated deployment of a toxin gene for developmental programmed cell death in bacteria.

Background Many microorganisms, including myxobacteria, cyanobacteria, and flexibacteria, move by gliding. Although gliding always describes a slow surface-associated translocation in the direction of the cell's long axis, it can result from two very different propulsion mechanisms: social (S) motility and adventurous (A) motility. The force for S motility is generated by retraction of type 4 pili. A motility may be associated with the extrusion of slime, but evidence has been lacking, and how force might be generated has remained an enigma. Recently, nozzle-like structures were discovered in cyanobacteria from which slime emanated at the same rate at which the bacteria moved. This strongly implicates slime extrusion as a propulsion mechanism for gliding. Results Here we show that similar but smaller nozzle-like structures are found in Myxococcus xanthus and that they are clustered at both cell poles, where one might expect propulsive organelles. Furthermore, light and electron microscopical observations show that slime is secreted in ribbons from the ends of cells. To test whether the slime propulsion hypothesis is physically reasonable, we construct a mathematical model of the slime nozzle to see if it can generate a force sufficient to propel M. xanthus at the observed velocities. The model assumes that the hydration of slime, a cationic polyelectrolyte, is the force-generating mechanism. Conclusions The discovery of nozzle-like organelles in various gliding bacteria suggests their role in prokaryotic gliding. Our calculations and our observations of slime trails demonstrate that slime extrusion from such nozzles can account for most of the observed properties of A motile gliding.

It is an already well established and experimentally proven fact that bacterial structures can participate in extra or intracellular accumulation of inorganic material. Myxoccocus coralloides and M. xanthus cells from cultures of 48 h or more presented signs of globular deformities. Further study of these deformities through transmission electron microscopy indicated that small crystalline forms of struvite were present but were sometimes destroyed by the mere impact of the electron beam.

We studied the possibility of struvite formation using killed cells of Myxococcus xanthus. Cells were killed by heat, UV light and sonication. In all cases, we show that struvite crystallization occurs and we propose that the dead cells or cell debris can act by themselves as heterogeneous crystallization nuclei. We also show that the slime, produced by Myxococcus in a large quantities, is not involved in this process.

Cell communication governs differentiation and morphogenesis in fruiting body formation by Myxococcus xanthus. Transmission of a small short-range intercellular signal by a protein called C factor directs multicellular pattern formation and coordinates the timing of major developmental events.

Nucleoside diphosphate (NDP) kinase catalyzes the transfer of the γ-phosphate from a nucleoside triphosphate to a nucleoside diphosphate. Human and rodent forms of this enzyme have been shown to be suppressors of metastasis. Crystals that diffract X-rays to high resolution have been obtained for the recombinant Myxococcus xanthus NDP kinase expressed in and purified from Escherichia coli. Two crystal forms have been obtained. Both forms are orthorhombic, space group I222 (or I212121) with a = 267·1 A , b = 74·0 A and c = 75·1 A for form I and a = 53·5 A , b = 74·0 A and c = 75·1 A for form II. Form I appears to have five molecules in the asymmetric unit approximately related to each other by a translation of 0·2 along the a axis. Diffraction data have been recorded to 1·9 A for form I and to 2·2 A for form II.

Summary Monoclonal antibodies (MCA) have been develped against cell surface antigens (CSA) of Myxococcus xanthus undergoing fruiting body formation. Three of these antibodies are directed against CSA which increase during development, six against CSA which decrease and three against CSA which show no change during development. Western-type immunoblots have been done to determine the molecular weights of the CSA to which the various MCA bind. Various applications of these MCA to the study of myxobacterial cell interactions are discussed.

Structural genes for the five major pectate lyases of Erwinia chrysanthemi, pelA, pelB, pelC, pelD and pelE, have been transferred and expressed in Myxococcus xanthus. These proteins, which are secreted by their original host, are also produced, mainly into the medium, by Myxococcus. These results are discussed in the context of current knowledge about secretion in bacteria.

Tn 5 lac is a transposon that fuses the transcription of lacZ to exogenous promoters. We generated 2374 Tn 5 lac insertion-containing strains of Myxococcus xanthus , a soil bacterium that undergoes multicellular development which culminates in the formation of spores. Thirty-six strains were identified that specifically increase β-galactosidase expression at some particular time during development and these expression times range from minutes after starvation initiates development to 24 hr, when sporulation begins. Different maximum levels of β-galactosidase expression were also observed and the maximum for many strains that begin β-galactosidase expression late in development was observed only if spores were disrupted. Seven of the 36 strains display mild to severe defects in aggregation and/or sporulation, as did an additional five strains whose β-galactosidase expression was not devlopmentally regulated. Restriction maps of the DNA adjacent to the Tn 5 lac insertions that are developmentally regulated and/or cause developmental defects show that most of the 41 insertions are in different regions of the Myxococcus genome. The developmentally regulated Tn 5 lac insertions described here provide a set of at least 29 new developmental markers for Myxococcus .

The calcium carbonate precipitation by several species of Myxococcus was investigated. The crystals were identified by x-ray diffraction as calcite and/or vaterite depending on the culture conditions employed.

The vegetative cell of Myxococcus xanthus has a wall about 250 A thick. Walls can be isolated from these cells by digesting heated or ethanol-treated cells with trypsin or chymotrypsin. Walls in the shape of spheres are obtained from heated cells while ethanol-treated cells yield rod-shaped walls. Walls isolated from heated cells are pigmented and are about 50% lipid, 5% nitrogen and 5% carbohydrate. Walls from ethanol-extracted cells are colorless and are lower in lipid and higher in nitrogen and carbohydrate components. Seventeen amino acids were identified in isolated walls of M. xanthus. Constituent sugars in the walls were: glucose, galactose, rhamnose and a hexosamine.