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Unfixed fruiting bodies of myxobacters have been viewed in great detail with a scanning electron microscope. Specimens of species of the genera Myxococcus, Chondrococcus, Archangium, Stelangium, Melittangium, Cystobacter, Polyangium, Stigmatella, and Chondromyces were examined. The desirability of using the scanning electron microscope for the study of the gross morphology of myxobacter structures has been clearly demonstrated.

SUMMARY: The life cycle in Sporocytophaga closely resembles that of the non-sporing eubacteria. The haploid microcyst germinates, the resulting cell containing two paired chromosomes reproducing vegetatively. An autogamous fusion and subsequent reduction division precede the maturation of the microcyst. Sporocytophaga differs from Myxococcus by the absence of fruiting body formation, and in the details of its nuclear cycle. These bacteria may possibly be regarded as the ancestors of the higher myxobacteria.

SUMMARY: The life cycle of Myxococcus fulvus consists of the following stages: germinating microcysts, young vegetative cells, intermediate cells, mature cells and resting microcysts. Germination takes place by simple elongation, or germ-tube formation. The nucleus of the germinating microcyst is a single oval or elongate body. The young vegetative cell should probably be referred to as multinucleate because the nucleus consists of a string of lobate bodies. In intermediate and mature cells the nucleus is either bi-lobed or oval, with the presence of entire edges. Details of the electron micrographs suggest a nuclear membrane. Microcysts normally have a single nucleus, and possibly possess nucleoli. Resting microcysts consist of a thin outer shell, a thick inner shell, cytoplasm and a nucleus.

Dworkin, Martin (Indiana University Medical Center, Indianapolis, Ind.). Nutritional requirements for vegetative growth of Myxococcus xanthus . J. Bacteriol. 84: 250–257. 1962.—This investigation was part of a program to clarify the environmental regulation of fruiting-body formation in a fruiting myxobacterium. By use of a dispersed-growing strain of Myxococcus xanthus , the nutritional requirements for vegetative growth have been defined. Exponential growth will take place on a medium containing 17 amino acids and salts. The generation time is 8 to 10 hr. Various optima have been established. There are no requirements for exogenous vitamins, and, with the exception of glycogen, a variety of organic materials do not significantly stimulate growth.

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.

Es wird uber die Bildung von Kriechspuren von Myxococcus rubescens auf Agarhangetropfen berichtet. Die Spuren werden als Rinnen gedeutet, die beim Kriechen der Zellen auf alteren Hangetropfenpraparaten entstehen und sich nicht mit der Vorstellung einer Fortbewegung der Zellen durch Schleimabsonderung vereinbaren lassen. Es wird in Erwagung gezogen, das Kontraktionsbewegungen der aktiv biegsamen Zelle zur Erklarung der Bewegungsart dienen konnten; damit steht auch das elastikotaktische Verhalten in Einklang. Die Zellteilung wird an lebendem Material im Agarhangetropfen beobachtet. Die von den meisten Untersuchern behauptete teigige Einschnurung und Ausziehung war unter diesen Bedingungen nicht festzustellen.

Norén, Börge (University of Wisconsin, Madison) and Kenneth B. Raper . Antibiotic activity of myxobacteria in relation to their bacteriolytic capacity. J. Bacteriol. 84: 157–162. 1962— Myxococcus virescens, M. fulvus, M. stipitatus, M. lacteus, Chondrococcus blasticus , and Chondromyces crocatus were tested for antibacterial activity, and all were found to secrete products that inhibited the growth of gram-positive eubacteria. The amount of inhibition varied with the myxobacterium employed and with the eubacterium used as a test organism. The growth of gram-negative eubacteria was in no case visibly affected by the antibiotic products. The experiments performed failed to indicate any positive relationship between the antibacterial activity and the bacteriolytic capacity of the six myxobacteria investigated.

Fruiting bodies of representative genera of the order Myxobacterales Jahn 1915 were examined by using a “Stereoscan” electron microscope (Cambridge Instrument Co.). Speciesof Myxococcus. Chondrococcus. Melittangium. Chondromyces, Archangium, and Stigmatella were examined. The instrument was found to be of value in studying the detail of fruiting bodies.

Es wird uber die Entwicklungsphysiologie von Myxobakterienfruchtkorpern berichtet. Fur die Entstehung und Differenzierung derselben sind Substrateinflusse weitgehend bestimmend. Durch einseitige Ernahrung mit Futterbakterien wurde bei Chondromyces apiculatus eine starke, bleibende Formveranderung erzielt. Zur Frage der Fortbewegung der Myxobakterienzellen werden Befunde mitgeteilt, die eindeutig fur eine Beteiligung des abgeschiedenen Schleims am Zustandekommen der Bewegung sprechen.

Although flagella are the best-understood means of locomotion in bacteria [1], other bacterial motility mechanisms must exist as many diverse groups of bacteria move without the aid of flagella [2–4]. One unusual structure that may contribute to motility is the type IV pilus [5,6]. Genetic evidence indicates that type IV pili are required for social gliding motility (S-motility) in Myxococcus, and twitching motility in Pseudomonas and Neisseria[6,7]. It is thought that type IV pili may retract or rotate to bring about cellular motility [6,8], but there is no direct evidence for the role of pili in cell movements. Here, using a tethering assay, we obtained evidence that the type IV pilus of Myxococcus xanthus functions as a motility apparatus. Pili were required for M. xanthus cells to adhere to solid surfaces and to generate cellular movement using S-motility. Tethered cells were released from the surface at intervals corresponding to the reversal frequency of wild-type cells when gliding on a solid surface. Mutants defective in the control of directional movements and cellular reversals (frz mutants) showed altered patterns of adherence that correlate reversal frequencies with tethering. The behavior of the tethered cells was consistent with a model in which the pili are extruded from one cell pole, adhere to a surface, and then retract, pulling the cell in the direction of the adhering pili. Cellular reversals would result from the sites of pili extrusion switching from one cell pole to another and are controlled by the frz chemosensory system.

Myxobacters were found to be common inhabitants of the arid soils from the Monterrey, Nuevo Leon, Mexico, area. Thirteen species of the genera Myxococcus, Archangium, Cystobacter, Stigmatella, Polyangium , and Chondromyces were isolated on a mineral salts agar supplemented with bakers' yeast and filter paper. Greater species diversity per soil sample was found in the region receiving 400 to 800 mm of annual rainfall as compared with soils from an area having only 200 to 400 mm of rainfall.

SummaryProgrammed cell death is of ultimate importance in embryonic development of animals. Now, programmed cell death has been shown to be an integral part of a multicellular developmental program in the bacterium Myxococcus xanthus.

Insertions of transposon Tn5 were used to examine the genetics of motility mutants in Myxococcus . Fifteen independent insertions of Tn5 were isolated that were linked to seven different loci that govern motility. Among the motility mutants that can be stimulated to move transiently by contanct with other cells, a one-to-one correspondence was confirmed between specificity of stimulation and genetic locus. There are six different specificities and six corresponding loci, as if each locus governs a different protein required for gliding motility.

SUMMARY: Chloramphenicol-resistant Myxococcus virescens were obtained by infecting myxococci with Escherichia coli specialized transducing phage P1CM. The drug-resistant myxococci were phenotypically unstable. They contained more than one type of plasmid; these plasmids were not found in the parent strain. Chloramphenicol-resistant E. coli were obtained by transformation with either a fraction of myxococcal DNA containing the plasmids or with P1CM prophage DNA. These transformants contained plasmids. Escherichia coli transformed by DNA from the myxococci contained both P1CM and myxococcal genes. Individual transformant clones differed in the genetic make-up of their plasmids. Among the myxococcal genes expressed in these plasmid-harbouring E. coli strains were a capacity for self-transmissibility and a pattern of phage sensitivity characteristic of R factor incompatibility group W. Escherichia coli transformed with P1CM prophage contained incomplete P1CM genomes; none of the chloramphenicol-resistant transformants produced P1CM phage particles. The significance of these findings for an understanding of mechanisms for the generation of R factors is discussed.

A promoterless trp-lac fusion fragment was inserted near one end of the bacterial transposon Tn5 in the correct orientation to fuse lacZ gene expression to promoters outside Tn5. The resulting transposon, Tn5 lac, retains the kanamycin-resistance gene of Tn5 and transposes in Escherichia coli at 6% the frequency of Tn5 to many different sites in a bacteriophage lambda target. Expression of beta-galactosidase, the product of the lacZ gene, from Tn5 lac insertions in phage lambda depends both on insertion into a transcription unit in the correct orientation and on the regulation of the promoter of the transcription unit, verifying that by transposition Tn5 lac can fuse lacZ expression to outside promoters. An insertion of Tn5 lac in bacteriophage P1 was isolated and used to introduce Tn5 lac into Myxococcus xanthus, a bacterium that undergoes multicellular development. Stable kanamycin-resistant transductants are obtained that contain no P1 DNA sequences but have Tn5 lac inserted at different sites in the Myxococcus chromosome. Individual transductants express different levels of beta-galactosidase. A chromogenic substrate of beta-galactosidase, 5-bromo-4-chloro-3-indolyl beta-D-galactoside, is toxic in Myxococcus when cleaved in large amounts. In principle, Tn5 lac could be used to assay transcription in any bacterium in which Tn5 can transpose and beta-galactosidase can be measured.

In 1892 Thaxter described the myxobacteria as “possessing a power of slow locomotion ... a distinctly visible movement characterizes the active rods and consists in a sliding locomotion in conjunction with lateral bending.” Almost one century later there are still conflicting ideas about the mechanism of gliding. At a genomic level it is evident that Myxococcus gliding is a complex phenomenon (Chapter 8). Elucidation of the enigma of gliding motility has been much slower than that for swimming motility of flagellated bacteria, since myxobacteria (and other gliders) have no obvious organelles of motility protruding from their cell envelopes. Indeed, gliding has recently been described as a “backwater” in the motility field (Allen 1981).

1. Myxococcus xanthus B and M. virescens V2 were compared with a view to establishing the control of their morphogenetic cycles. Both organisms are typical myxococci and on solid media with low concentrations of nutrient they form fruiting bodies, within which vegetative cells convert to myxospores. Ultrathin sections of vegetative M. virescens resembled those of M. xanthus and contained prominent heavily stained bodies, presumed to be polyphosphate granules. Shadowed preparations showed fimbriae associated with M. xanthus but not with M. virescens. 2. M. xanthus B converted to myxospores in liquid medium in response to certain alcohols. M. virescens V2 produced phase-refractile spheres, which were not viable and had an unusual ultrastructure. 3. The distributions of fruiting bodies on solid media containing 0.02% Casitone were recorded for the two species and were compared with a Poisson distribution. Cells responded to differences in cell density in a manner suggestive of a response to a chemotactic attractant. Cells growing vegetatively and also cells forming fruiting bodies produced 3′,5′-cyclic adenosine monophosphate (cAMP) as measured by the incorporation of exogeneous [3H] adenosine into cAMP. 4. The significance of these findings for theories of fruiting body formation are discussed.

CELL INTERACTIONS . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 539 OVERVIEW OF D/CTYOSTELIUM AND MYXOCOCCUS DEVELOPMENT . . . . . . . . . . 540 Dictyostelium . . . . . . . . . . . . . . . . . . . . . . ....... '" . . . . . . . . . . . . . . . . . . . ......... 541 Myxococcus.. . . . .. . . . . . . .... . . . . . . . . . . . . . . . . . . . ....... . . . . . . . . . . . . . . . . . . . . . . ....... . . . . . . . . .. . . . . . . 541 Common qualities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 541 INITIATION-D/CTYOSTELIUM . . . . . ... .... .. . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542 INITIATION-MYXOCOCCUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . 543 INTERCELLULAR SIGNALLING-D/CTYOSTEUUM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543 INTERCELLULAR SIGNALLING-MYXOCOCCUS.. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545 AGGREGA TION-DICTYOSTELIUM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 548 AGGREGA TION-MYXOCOCCUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . 550 PLEIOTROPY-D/CTYOSTELIUM . . . . . ........ . . . . . . . . .... . . . . . . . . . . . . . . .. 55 1 PLEIOTROPY-MYXOCOCCUS . . . . . . . . . . . . . . . . .. . . . . . . ...... 553 Sporulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 553 Developmental Markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...... . . .. . . . . . . . . . . 554 PAUCITY OF ESSENTIAL DEVELOPMENTAL FUNCTIONS .. ........ . . . . . . . . . ........ 555 EVOLUTION OF MULTICELLULARITy. . .. ..... . . .. . . ....... ........ . . . 556 CONCLUSIONS . . .. . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . .. . . .... . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . .. . . . . . 559

Sporopollenin, a resistance material previously found only in algae, fungi, pollen grains, and in some plant spores, has been found in four species of Myxococcus. Sporopollenin was isolated from vegetative cells and myxospores of the myxobacteria tested but it was not detected in any of the other bacteria tested.

Silicified flake conglomerates andin situstratiform stromatolites of the Upper Proterozoic (c.700–800 Ma) Limestone-Dolomite ‘Series’, central East Greenland, contain well preserved microfossils. Five stratigraphic horizons within the 1200 m succession contain microbial mat assemblages, providing a broad palaeontological representation of late Proterozoic peritidal mat communities. Comparison of assemblages demonstrates that the taxonomy and diversity of mat builder, dweller, and allochthonous populations all vary considerably within and among horizons. The primary mat builder in most assemblages isSiphonophycus inornatum, a sheath-forming prokaryote of probable but not unequivocally established cyanobacterial affinities. An unusual low diversity unit in Bed 17 is dominated by a different builder,Tenuofilum septatum, while a thin cryptalgal horizon in Bed 18 is built almost exclusively bySiphonophycus kestron.Although variable taphonomic histories contribute to observed assemblage variation, most differences within and among horizons appear to reflect the differential success or failure of individual microbial populations in colonizing different tidal flat microenvironments. Twenty-two taxa are recognized, of which two are described as new:Myxococcoides stragulescensn.sp. andScissilisphaera gradatan. sp.

We have shown that the blood anticoagulant activity (BAA) secreted by Myxococcus xanthus (designated myxaline) is a heat-stable molecule; a high-molecular-mass extracellular fraction also with an apparent BAA is a thermolabile protease. This property allowed us to assay the BAA content in crude boiled culture supernatants and to study the conditions under which it is produced. Heat-stable BAA is strictly extracellular and its production is restricted to vegetative growth in M. xanthus. Unlike the other extracellular proteins, its production is not affected by mutations that regulate secretion; mutations that modify the extracellular proteolytic activity do not modulate the amount of myxaline produced either. Several other species of Myxococcus and one other myxobacterial species produce a heat-stable BAA during vegetative growth.

Myxococcus xanthus, an organism whose motility involves cell interactions, normally bears pili. Myxococcal pili are found only at cell poles, are less than 10 nm in diameter, and may be longer than a cell. Myxococcus has two basic patterns of cell movement, adventurous (A-motility) and social (S-motility). Pili are found to be completely correlated with the presence of S-motility. (The S-motility pattern has many groups of cells, almost no single cells, and is governed by a set of genes called system S.) On the other hand, A-motility is in dependent of piliation. (The A-motility pattern has many single, isolated cells and it is governed by a second set of genes called system A.) Electron microscopic examination of more than 40 genetically different strains shows that all A+S+ (wild-type) and A-S+ strains have pili, but A+S- and A-S- strains lack them. Mutations in four different loci belonging to system S were tested and were found to stop productions of pili: the loci sg1A, sg1B, sg1G, and tg1. When brought into contact with tg1+ cells, cells of a tg1- strain, which lack pili, become phenotypically S+, produce pili, and become S-motile. Both motility and the production of pili are transient when initiated in this way. Thus it appears that pili permit cells that are close to one another to move.

THE Myxobacteriaceae are unique among prokaryotes in their development cycle. Vegetative cells are Gram-negative bacilli which undergo binary fission as in other prokaryotes; alternatively, the cells can aggregate on solid surfaces to form fruiting bodies in which the bacteria undergo conversion to myxospores. In Myxococcus xanthus and related species a simple fruiting body is formed in which spherical myxospores are surrounded by extracellular polysaccharide slime1. In at least one strain of M. xanthus, synchronous myxospore formation can be obtained in liquid culture through induction with glycerol and other agents2. The entire bacillus undergoes conversion to the myxospore form; there is no apparent loss of cell material such as is observed in the morphogenesis of Gram-positive bacilli to endospores at the expense of cell wall and surface material shed on emergence of the mature spore. The fate of the Myxococcus surface polymers is thus of particular interest.

Induced by starvation, the development of fruiting bodies by Myxococcus xanthus on glass and plastic surfaces under a layer of liquid was followed microscopically. Calcium ions and a neutral pH were required for development of a Myxococcus strain that grew dispersed in liquid culture. Initially asymmetric aggregates later became round, and sporulation followed aggregation.

SUMMARY: An investigation has been made of the sequence of morphological events involved in the processes of microcyst formation and germination in the fruiting myxobacterium Myxococcus xanthus. By using time-lapse photo-micrographs and phase-contrast microscopy of living cells, microcyst formation is shown to involve a shortening and thickening of the entire vegetative cell with a subsequent increase of refractility. Germination is preceded by the casting off of a sheath followed by the gradual elongation and loss of refractility of the cell. Vegetative rods will readily form spheroplasts when exposed to a variety of conditions including sulphydryl compounds. The necessity for distinguishing between spheroplasts and microcysts is pointed out.

Association of a Steroid and a Pigment with a Diffusible Fruiting Factor in Myxococcus virescens

ALTHOUGH great interest has been taken in recent years in isolating antibiotics from various groups of micro-organisms, Myxobacteria have received so far very little attention. Several workers have reported the lysis of bacteria (Eubacteria) by species of Myxobaeteria; but no satisfactory evidence has been produced that living cells are attacked. It has been shown by Singh1, who used a large number of strains of bacteria, that certain species of Myxococcaceae undoubtedly cause lysis of both Gram-positive and Gram-negative living bacteria upon solid media. Oxford and Singh2 and Oxford3 have shown that a strain of Myxococcus virescens growing on cell-free medium is able to produce two substances, an exo-cellular lytic (proteolytic) enzyme and an antibiotic. Noren4 has confirmed and extended this work to other species of Myxobacteria and has devised more suitable media for the production of the proteolytic enzyme and the antibiotic. The present work deals with the lysis of human pathogenic bacteria by two species of Myxococcus.

THE genus Chondromyces was named and illustrated, but not described, by Berkeley and Curtis in 1857 in Berkeley's1 “Introduction to Cryptogamic Botany”. It was apparently next seen by Thaxter2, who reported that he grew it in pure culture. In 1913, this species was stated by Pinoy3 to grow only in the presence of Micrococcus. Beebe4 reported the presence of C. crocatus; but attempts to purify the organism failed completely though it grew readily with various bacteria in mixed culture. Kuhlwein5 stated that C. crocatus could not be grown in pure culture and that it was a symbiotic form. Oetker6, recently, has shown that several species in the genera Myxococcus and Podangium can grow upon yeast and algae.

Three novel compounds, namely, phenoxan, phenalamide A1, and thiangazole, were found to suppress HIV-1 replication in cell cultures. The compounds were discovered by screening crude extracts from myxobacteria and were isolated from two strains of Polyangium sp. and a strain of Myxococcus stipitatus. Their structures have been elucidated. The cytotoxic concentrations for MT-4 cells were 6.6 μM for phenoxan, 102 μM for phenalamide A1, and 4.7 μM for thiangazole. Phenoxan inhibited the HIV-1-dependent cell death at concentrations of as low as 6.6 nM. Phenalamide A1 could prevent the HIV-1 infection of MT-4 cells even at concentrations of 1.02nM, and thiangazole at 4.7 pM. In our assay thiangazole is at least 100 times more active than AZT. The compounds could not prevent syncythia formation induced by HIV-1. However, like HEPT (Baba et al., 1989; Miyasaka et al., 1989) and TIBO (Pauwels et al., 1990) derivatives they are highly specific since they could not interfere with HIV-2ben dependent MT-4 cell death. HIV-1 RT activity was inhibited by 50% by 376 μM phenoxan, 386 μM phenalamid A1, or 263 μM thiangazole. Since these concentrations are approximately 50000 times higher than their minimum concentrations active in cell cultures, RT-inhibition does not appear to be the major mechanism of HIV-inhibition of the new agents.

Myxococcus xanthus is a bacterial model in microbial developmental biology and social evolution. Here, I present the 57.0-kb circular genomic sequence of the wild-type Myxococcus phage Mx4, with a GC content of 70.1%. Annotation predicted 97 protein-coding genes. Head-neck-tail protein classification assigns Mx4 to the tailed, Mu-like members of the family Myoviridae of type 1 (cluster 8).

From the culture broth of the myxobacterium, Corallococcus (Myxococcus) coralloides, three new antibiotics have been isolated: corallopyronin A, B and C. The compounds, which are chemically related to the recently discovered myxopyronins, act mainly on Gram-positive bacteria, with MIC values between 0.1 and 10 micrograms/ml, and only exceptionally or at much higher concentrations (MIC values; 100 and more micrograms/ml) on Gram-negatives. They do not inhibit eukaryotic organisms and show no toxicity for mice (sc). The corallopyronins appear to block specifically eubacterial RNA polymerase.

Myxococcus xanthus is a bacterium with an interest for studies of development because it has an organized multicellular phase in its life cycle. Bacteriophage Pl can adsorb to M. xanthus and inject its DNA into this organism despite the wide taxonomic gap separating myxococcus from Escherichia coli, the source of Pl. A specialized transducing derivative of Pl, called PlCM, can carry a gene for chloramphenicol resistance from E. coli into M. xanthus and generate unstable drug-resistant strains.

Autoplaquing has been observed in Myxococcus strains freshly isolated from soil. Initial observations suggest that this phenomenon is not induced by elevated temperature or visible light; we suggest that it may be the result of a derangement in the developmental autolytic mechanism within the cell.