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PubMed1985

Immunomodulation by myxospores of Myxococcus xanthus.

Glycerol-induced myxospores of Myxococcus xanthus caused non-specific modulation of humoral and cellular immune responses in laboratory animals. The number of cells which formed specific haemolysins in spleens of mice immunized with sheep erythrocytes was increased when 0.5 X 10(8) myxospores were inoculated 2 d after the erythrocytes, and decreased when myxospores were injected 2 d before or at the same time as the erythrocytes. Both the IgG primary response and the secondary response to erythrocytes were decreased in rabbits after pretreatment with 2 X 10(8) myxospores per rabbit. Delayed-type hypersensitivity to sheep erythrocytes was also suppressed in mice after intraperitoneal (i.p.) injection of 0.3 X 10(8) myxospores. One day after i.p. injection of myxospores, neither an inflammatory response nor bone marrow cell depletion was observed in mice. These results support the idea that M. xanthus myxospores possess diverse immunomodulation properties apparently due to factors different from the classical LPS of Gram-negative bacteria.

Animals↗
PubMed1976

Extrachromosomal DNA in chloramphenicol resistant myxococcus strains.

The presence of extrachromosomal DNA in strains of Myxococcus xanthus and M fulvus was examined by rate-zonal centrifugation of radioactively-labelled DNA in 'cleared lysates'. All the strains examined contained extrachromosomal DNA, with the exception of M. xanthus FBt. Chloramphenicol resistance is inducible in M. xanthus FBt. A peak of extrachromosomal DNA, containing covalently closed molecules, was found in one of the induced strains, implying that induction of chloramphenicol resistance is associated with the production of a plasmid. By incubating R+ strains of Escherichia coli with myxococci, R factor-mediated chloramphenicol resistance can be introduced into the latter. Evidence of extra chromosomal DNA in a derivative of M. xanthus with chloramphenicol resistance from R factor RI. 19 unique to the chloramphenicol strain, was obtained. By using a double-labelling technique, several chloramphenicol-resistant strains of M. fulvus M were examined. Evidence for a peak, unique for the chloramphenicol-resistant strain, was found in a strain with resistance derived from the R factor, S-a, but not from comparable strains with resistance derived from R factors R57b, R1. 19 and R478.

Chloramphenicol↗
PubMed1990

Cell motility is required for the transmission of C-factor, an intercellular signal that coordinates fruiting body morphogenesis of Myxococcus xanthus.

There are striking similarities between the developmental phenotypes of two different mutant classes of Myxococcus xanthus. The first class, mglA mutants, are nonmotile under all conditions tested. The second class, csgA mutants, are motile but belong to a class of signal-defective developmental mutants that cannot develop alone but will develop when mixed with intact wild-type cells. Nevertheless, both csgA and mglA mutants fail to aggregate properly or to sporulate when induced to form fruiting bodies. An mglA mutation and a csgA mutation affect expression of a panel of lacZ fusions to developmental genes in the same way, indicating that nonmotile cells and csgA cells arrest development at a similar stage. One explanation for the similarity of developmental phenotypes between these mutants is that motility is required for the csgA-mediated cell interaction. In support of this hypothesis, we report that C-factor, a protein purified from nascent wild-type fruiting bodies based on its ability to rescue csgA mutant fruiting body development, also rescues sporulation and expression of beta-galactosidase from developmentally controlled lacZ fusions in mglA strains, apparently without restoring their motility. Wild-type levels of active C-factor can be purified from mglA cells, yet intact mglA cells do not rescue csgA cells upon cell-cell mixing. Intact wild-type cells are unable to restore the sporulation and beta-galactosidase expression of mglA mutants. These results support the hypothesis that donor and responder cell motility is required for C-factor transmission between cells during development.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Proteins↗
PubMed1990

Development-specific sigma-factor essential for late-stage differentiation of Myxococcus xanthus.

The gene for a developmentally expressed sigma-factor, sigB, has been isolated from Myxococcus xanthus by use of the sigA gene (formerly rpoD) of the vegetative sigma-factor as a probe. The sequence of sigB has been determined, and an open reading frame of 193 amino acid residues (Mr = 21,551) was identified. The amino-terminal region of SigB contains 69 residues, of which 35 are identical (50% identity) to the region of SigA required for core RNA polymerase binding and initiation of RNA polymerization. SigB also possesses many features commonly found in other prokaryotic sigma-factors. Analysis of an M. xanthus strain carrying a sigB-lacZ fusion gene revealed that sigB is expressed from a middle to late stage of differentiation corresponding to the period from the onset of sporulation to late development. A sigB deletion mutant displayed normal mound formation and sporulation; however, production of the ops gene product in myxospores of the delta sigB strain was shown to be blocked. Myxospores from the sigB deletion strain also exhibited severe defects in stability and viability during late development. Our data indicate that sigB encodes a sigma-factor essential for the maturation of myxospores at a late stage of M. xanthus differentiation. Our results also suggest that differentiation of M. xanthus is regulated by development-specific sigma-factors.

Amino Acid Sequence↗
PubMed1984

Production and properties of a bacteriocin from Myxococcus coralloides D.

Myxococcus coralloides D was found to produce a substance with a narrow range of antibacterial activity. This substance was produced during the exponential growth phase and was not inducible by ultraviolet light or mitomycin C treatment. The bacteriocin was precipitable by ammonium sulphate, and showed resistance to heat (100 degrees C for 10 min), trypsin, lysozyme, beta-glucuronidase, DNase, RNase, acetone, ethyl ether, urea and mercaptoethanol; it was partially destroyed by pronase and inactivated at extreme pH values. Electron microscopy did not reveal any phage-like particles associated with bacteriocin activity.

Bacteria↗
PubMed1994

Characterization of a Pseudomonas aeruginosa gene cluster involved in pilus biosynthesis and twitching motility: sequence similarity to the chemotaxis proteins of enterics and the gliding bacterium Myxococcus xanthus.

The type 4 pili of Pseudomonas aeruginosa are important cell-associated virulence factors that play a crucial role in mediating (i) bacterial adherence to, and colonization of, mucosal surfaces, (ii) a novel mode of flagella-independent surface translocation known as 'twitching motility', and (iii) the initial stages of the infection process for a number of bacteriophages. A new set of loci involved in pilus biogenesis and twitching motility was identified based on the ability of DNA sequences downstream of the pilG gene to complement the non-piliated (pil) strain, PAO6609. Sequence analysis of a 3.2 kb region directly downstream of pilG revealed the presence of three genes, which have been designated pilH, pilI, and pilJ. The predicted translation product of the pilH gene (13,272 Da), like PilG, exhibits significant amino acid identity with the enteric single-domain response regulator CheY. The putative PilI protein (19,933 Da) is 28% identical to the FrzA protein, a CheW homologue of the gliding bacterium Myxococcus xanthus, and the PilJ protein (72,523 Da) is 26% identical to the enteric methyl-accepting chemotaxis protein (MCP) Tsr. Mutants containing insertions in pilI and pilJ were severely impaired in their ability to produce pili and did not translocate across solid surfaces. The pilH mutant remained capable of pilus production and twitching motility, but displayed an altered motility pattern characterized by the presence of many doughnut-shaped swirls. Each of these pil mutants, however, produced zones that were at least as large as the parent in flagellar-mediated swarm assays. The sequence similarities between the putative pilG, H, I and J gene products and several established chemotaxis proteins, therefore, lend strong support to the hypothesis that these proteins are part of a signal-transduction network that controls P. aeruginosa pilus biosynthesis and twitching motility.

Amino Acid Sequence↗
PubMed1976

Nuclear activity and cell division in the microcysts of Myxococcus fulvus demonstrated by electron micrography of sections.

Electron micrographs of sectioned fruiting bodies confirm that, in Myxococcus fulvus, approximately 10% of mature microcysts show appearances interpretable as typical bacterial nuclear activity and cell division. This suggests a simple mechanism for fruiting body development, and its existence bears upon the validity of the classical descriptions of microcyst maturation in myxobacteria.

Cell Division↗
PubMed1975

On the utilization in vivo of lycopene and phytoene as precursors for the formation of carotenoid glucoside ester and on the regulation of carotenoid biosynthesis in Myxococcus fulvus.

During th logarithmic phase of growth of the myxobacterium Myxococcus fulvus the specific carotenoid content and the molar ratio of the two main carotenoids keto-torulene (3',4'-didehydro-beta,psi-caroten-4-one, 15%) and myxobacton ester (1'-glucosyloxy-3',4'-didehydro-1',2'-dihydro-beta,psi-caroten-4-one ester, 80%) are highly constant. When the formation of these carotenoids was prevented by an inhibitory block at the level of phytoene desaturation, the normal specific content is rapidly reached after release of this block by a two-three-fold enhanced rate of synthesis. The experimentally accumulated phytoene molecules however, are not used as a precursor pool for the formation of the coloured carotenoids. The absolute amount of phytoene does not decrease, although a considerable molecule exchange between this pool and the pathway occurs. Furthermore, experimentally accumulated lycopene is only converted into myxobacton ester when the carotenogenic pathway is blocked at an earlier step, at the level of phytoene desaturation. Without this blockage the lycopene pool remains unaffected. The results are discussed in terms of arrangement of the carotenogenic enzymes in a sort of assembly line in association with the cytoplasmic membrane. Four sites of control are suggested in this pathway.

Carotenoids↗
PubMed1990

Cell alignment required in differentiation of Myxococcus xanthus.

During fruiting body morphogenesis of Myxococcus xanthus, cell movement is required for transmission of C-factor, a short range intercellular signaling protein necessary for sporulation and developmental gene expression. Nonmotile cells fail to sporulate and to express C-factor-dependent genes, but both defects were rescued by a simple manipulation of cell position that oriented the cells in aligned, parallel groups. A similar pattern of aligned cells normally results from coordinated recruitment of wildtype cells into multicellular aggregates, which later form mature fruiting bodies. It is proposed that directed cell movement establishes critical contacts between adjacent cells, which are required for efficient intercellular C-factor transmission.

Bacterial Proteins↗
PubMed1985

Transposon tagging to detect a latent virus in Myxococcus xanthus.

Transposon mutagenesis of the bacterium Myxococcus xanthus with the transposon Tn5 revealed a special class of bacterial mutants that transduced the transposon through culture supernatant fluids. Virus-like particles copurified with transducing activity. Transposon tagging for detecting these virus-like particles may be generally useful in isolating endogenous viral agents capable of transferring genetic information between cells.

Bacteriophages↗
PubMed1973

Bactericidal action of an antibiotic produced by Myxococcus xanthus.

Myxococcus xanthus produced an antibiotic during the end of its exponential growth phase which was capable of inhibiting growth of several gram-positive and gram-negative bacteria. The antibiotic was bactericidal to growing cultures only; chloramphenicol inhibited the bactericidal action of the antibiotic. Upon addition of the antibiotic to Escherichia coli B, deoxyribonucleic acid and ribonucleic acid as well as turbidity of the culture continued to increase even after the viable count decreased; the culture lysed about 60 min after addition of sufficient concentrations of the antibiotic. Spheroplasts could be prepared if the antibiotic was added to a culture growing in the presence of high concentrations of sucrose and MgSO(4). Mutants of M. xanthus FB which are incapable of fruiting body formation or glycerol-induced myxospore formation also produced the antibiotic. A mutant of E. coli resistant to the purified antibiotic was isolated in order to study the role of the antibiotic in the predatory behavior of myxococci.

Anti-Bacterial Agents↗
PubMed1975

Chloramphenicol resistance in Myxococcus xanthus.

Derivatives of Myxococcus xanthus FB(t) resistant to chloramphenicol (25 mug/ml) arose spontaneously with a frequency of approximately 10(-7). One of these organisms (FB(t)Cam(1) (r)) was characterized. FB(t)Cam(1) (r) showed a unique type of phenotypic instability. After transfer from medium containing chloramphenicol to medium lacking the drug, resistance was lost after approximately one generation. The loss resulted in a sharp drop in the total number of chloramphenicol-resistant organisms and was not due to segregation of chloramphenicol-susceptible organisms during growth. Cell-free extracts of strain FB(t)Cam(1) (r) converted chloramphenicol to acetyl chloramphenicols in a fashion implicating activity of chloramphenicol acetyltransferase. This activity was lost simultaneously with the loss of chloramphenicol resistance after removal of the drug from cultures. Organisms with a similar phenotype to FB(t)Cam(1) (r) could be produced at high frequencies when strain FB(t) was exposed to low concentrations of chloramphenicol (2 to 5 mug/ml), to 3-acetylchloramphenicol (25 mug/ml), or to 1,3-diacetylchloramphenicol (25 mug/ml). Since strain FB(t) is capable of deacetylating acetyl chloramphenicols, these effects are probably all due to low concentrations of chloramphenicol. In the presence of chloramphenicol, FB(t)Cam(1) (r) produced fruiting bodies and myxospores on fruiting agar; however, glycerol-induced myxospore formation was inhibited. In the absence of the antibiotic, chloramphenicol resistance was maintained by glycerol-induced myxospores.

Chloramphenicol↗
PubMed1970

Stable messenger ribonucleic acid and germination of Myxococcus xanthus microcysts.

We have examined germination, protein synthesis and ribonucleic acid (RNA) synthesis by microcysts of the fruiting myxobacterium Myxococcus xanthus. The morphological aspects of microcyst formation were completed at about 2 hr after induction had begun. In such microcysts, germination, RNA synthesis, and protein synthesis were inhibited by actinomycin D (Act D). At 6 hr after induction, germination and protein synthesis had become relatively resistant to Act D, whereas RNA synthesis was inhibited by about 95%. Experiments with (3)H-Act D indicated that the deoxyribonucleic acids of both young and old microcysts bind Act D equally. Resistance of germination to Act D was acquired 4 to 5 hr after induction of microcyst formation, and was due to an Act D-sensitive synthesis at that time. Vegetative cells and microcysts were pulsed with uridine-5-(3)H and chased for 60 min; the RNA was extracted and analyzed by means of sucrose density gradient centrifugation and gel electrophoresis. Both microcysts and vegetative cells were found to contain grossly the same types of RNA in the same proportions. RNA pulse-labeled in microcysts was more stable than that in vegetative cells. No particular portions of the microcyst pulse-labeled RNA were selectively stabilized. These data indicate that a stable messenger RNA required for synthesis of germination proteins was synthesized during microcyst formation. This may be the same as the RNA synthesized 4 to 5 hr after initiation of microcyst formation. We suggest that the existence of such stable messenger RNA in microcysts is consistent with the limited biosynthetic activities of such cells.

Bacteria↗
PubMed1970

Induction of morphogenesis by methionine starvation in Myxococcus xanthus: polyamine control.

The induction of mycrocyst formation by methionine starvation was demonstrated in Myxococcus xanthus by several methods. Growing in a defined medium (M(1)), M. xanthus had a doubling time of 6.5 hr. Four amino acids-leucine, isoleucine, valine, and glycine-were required for growth under these conditions. When the concentration of several amino acids in the medium was reduced (M(2)), the doubling time increased to 10 to 12 hr, and a requirement for methionine was observed. Methionine starvation led to a slow conversion of the population to microcysts. Under conditions of methionine prototrophy (M(1)), microcyst formation could still be triggered in exponentially growing cells by the addition of either 5 mm ethionine or 0.1 m isoleucine plus 0.1 m threonine, feedback inhibitors of methionine biosynthesis. Vegetative growth in the absence of methionine was obtained in medium M(2) if the leucine concentration was raised to its level in medium M(1). Thus, methionine biosynthesis is controlled by the exogenous concentration of the required amino acid, leucine. During an examination of the effects of methionine metabolites on microcyst formation, the involvement of polyamines in morphogenesis was uncovered. Putrescine (0.05 m) induced the formation of microcysts; spermidine (2 to 5 mm) inhibited induction by methionine starvation, ethionine, or high isoleucine-threonine. Spermidine was the only polyamine detected in M. xanthus (16.0 mug/10(9) cells). Its concentration decreased by more than 50% shortly after microcyst induction by high isoleucine-threonine. It is postulated that spermidine is an inhibitor of microcyst induction; when spermidine formation is blocked by methionine starvation, morphogenesis is induced.

Amines↗
PubMed1970

Ribonucleic acid synthesis during microcyst formation in Myxococcus xanthus: characterization by deoxyribonucleic acid-ribonucleic acid hybridization.

The technique of deoxyribonucleic acid-ribonucleic acid (RNA) hybridization was used to compare the RNA synthesized during vegetative growth and microcyst formation in Myxococcus xanthus. All classes of RNA, including ribosomal RNA, were synthesized during microcyst formation. The results indicate that the ribosomal RNA synthesized during microcyst formation was indistinguishable from that made during vegetative growth. Hybridization competition experiments demonstrated that certain messenger RNA species are synthesized only during vegetative growth, whereas others are synthesized only during microcyst formation. The synthesis of a new species of RNA polymerase does not appear to be responsible for differential transcription during morphogenesis in M. xanthus since the rifampicin sensitivity of transcription was conserved during microcyst formation.

Bacteria↗
PubMed1970

Potassium uptake during microcyst formation in Myxococcus xanthus.

The kinetics of (42)K uptake by Myxococcus xanthus during vegetative growth and microcyst formation were determined. In the medium studied, growing cells concentrated potassium about 100-fold, yielding an intracellular concentration of 147 mm. The influx of K(+) in growing cells was 17 +/- 3 pmoles of K(+)/cm(2) min. About 5 hr after induction of vegetative cells to microcysts, the K(+) influx decreased and the intracellular concentration fell. By 18 hr after induction, there was no measurable influx of K(+), and the intracellular concentration of potassium was less than 29 mm. There was, however, considerable binding of K(+) to the "surface" of microcysts. It is postulated that the greatly reduced intracellular concentration of potassium helps to maintain the microcyst in its dormant state and protects it against enzymatic break-down.

Bacteria↗
PubMed1970

Gliding motility mutants of Myxococcus xanthus.

Two gliding motility mutants of Myxococcus xanthus are described. The semimotile mutant (SM) originated by high-frequency segregation from the motile FB(t) strain. Segregation was enhanced by acridine dye treatment. SM cells glide only when apposed to other cells in a swarm. The nonmotile strain (NM) originated by mutation from SM. NM cells neither glide individually nor cooperatively. FB(t), SM, and NM are indistinguishable with respect to fine structure, vegetative growth rate, glycerol-induced microcyst formation, spheroplasting, bacteriophage sensitivity, and responses to light. The motility mutants are more resistant to penicillin and more sensitive to actinomycin D than is the gliding wild type. The NM mutant is also a morphogenetic mutant; it is unable to form fruiting bodies.

Acridines↗
PubMed1971

Division cycle of Myxococcus xanthus. II. Kinetics of stable and unstable ribonucleic acid synthesis.

The kinetics of stable and unstable ribonucleic acid (RNA) synthesis during the division cycle of Myxococcus xanthus growing in a defined medium was determined. Under these conditions, M. xanthus contains one chromosome which is replicated during 80% of the cell cycle. Stable RNA synthesis was measured by pulselabeling an exponential-phase culture with radioactive uridine and then preparing the cells for quantitative autoradiography. By measuring the size of individual cells as well as the number of grains, the rate of stable RNA synthesis as a function of cell size was determined. Unstable RNA synthesis during the division cycle was determined by correlating the data for stable RNA synthesis with the relative amounts of stable and unstable RNA labeled during the short pulse. The data reported here demonstrate that: (i) cells synthesize both stable and unstable RNA throughout the division cycle; (ii) the rate of stable RNA synthesis increases in two discrete steps, corresponding to average ages of 0.15 and 0.75 generations; (iii) the rate of unstable RNA synthesis exhibits an initial rise, followed by a relatively constant rate of synthesis, and finally, a burst of unstable RNA synthesis prior to septum formation. The half-life of unstable RNA of M. xanthus, generation time of 390 min at 30 C, was 4 min. Comparison of the rates of stable and unstable RNA synthesis indicates noncoordinate RNA synthesis within the normal division cycle.

Autoradiography↗