Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Myxococcus”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16Linked to original sources
PubMed1993

The lonD gene is homologous to the lon gene encoding an ATP-dependent protease and is essential for the development of Myxococcus xanthus.

Myxococcus xanthus contains two genes (lonV and lonD) homologous to the Escherichia coli lon gene for an ATP-dependent protease. We found that the lonD gene encodes a 90-kDa protein consisting of 827 amino acid residues. The lonD gene product shows 49, 48, and 52% sequence identity to the products of the M. xanthus lonV, E. coli lon, and Bacillus brevis lon genes, respectively. When a lonD-lacZ fusion was used, lonD was expressed during both vegetative growth and development. However, while lonD-disrupted strains were able to grow normally vegetatively, the development of M. xanthus was found to be arrested at an early stage in these strains. The mutant strains were able to form neither fruiting bodies nor myxospores.

ATP-Dependent Proteases↗
PubMed1993

Oar, a 115-kilodalton membrane protein required for development of Myxococcus xanthus.

Myxococcus xanthus is a developmental gram-negative bacterium which forms multicellular fruiting bodies upon nutrient starvation. This bacterium was found to contain a 115-kDa membrane protein which separated with the inner membrane fraction by sucrose density gradient centrifugation. The gene for this protein was cloned, and its DNA sequence was determined. The deduced amino acid sequence consists of 1,061 residues. This protein contains a putative signal sequence and many short segments, found scattered throughout the entire protein, that have sequence similarities with OmpA, a major outer membrane protein of Escherichia coli. Thus, the gene was designated oar (OmpA-related protein). A second open reading frame was found 36 bases downstream of the oar termination codon. This open reading frame encodes a protein of 236 residues and contains a putative lipoprotein signal sequence. An aor disruption mutation (delta oar) showed no effect on vegetative growth but caused abnormal morphogenesis during development and reduced myxospore formation. When examined with a light microscope, delta oar cells were unable to aggregate on developmental agar, indicating that Oar is required for cellular adhesiveness during development.

Amino Acid Sequence↗
PubMed1993

FrzCD, a methyl-accepting taxis protein from Myxococcus xanthus, shows modulated methylation during fruiting body formation.

The frizzy (frz) genes of Myxococcus xanthus are required to control directed motility during vegetative growth and fruiting body formation. FrzCD, a protein homologous to the methyl-accepting chemotaxis proteins from enteric bacteria, is modified by methylation in response to environmental conditions. Transfer of cells from rich medium to fruiting medium initially caused rapid demethylation of FrzCD. Subsequently, the amount of FrzCD increased, but most remained unmethylated. At about the time of mound formation (9 h), most of the FrzCD was converted to methylated forms. Dispersal of developing cells (10 h) in buffer led to the demethylation of FrzCD, whereas concentration of these cells caused methylation of FrzCD. Some mutants which were unable to form fruiting bodies still modified their FrzCD during incubation under conditions of starvation on a surface.

Bacterial Proteins↗
PubMed1993

devRS, an autoregulated and essential genetic locus for fruiting body development in Myxococcus xanthus.

Two Tn5 lac insertions into the Myxococcus genome at sites omega 4414 and omega 4473, which are separated by 550 nucleotides, inactivate fruiting body development. Sporulation is decreased 100- to 10,000-fold. At least two genes, devR and devS, are transcribed in this region, probably as an operon. Expression of devR begins by 6 h after starvation has initiated development. On the basis of their nucleotide sequences, devR and devS are expected to encode proteins of 302 and 214 amino acids, respectively. Dev+ function can be restored by a segment of 7.8 kb cloned from the devRS region of wild-type cells. Two experiments show that devR expression is under strong negative autoregulation. beta-Galactosidase is expressed at a higher level from a transcriptional devR::lacZ fusion when the fused operon is in a dev strain than when it is in the dev/dev+ genetic background of a partial diploid. There is more mRNA accumulation from the devRS region in the dev strain than in a rescued dev/dev+ tandem duplication strain. Sporulation rescue is correlated with some degree of negative autoregulation, even though sporulation is not inversely proportional to beta-galactosidase expression from omega 4414. A second level of regulation is suggested by complementation of dev by dev+ in duplication strains. The expression of devRS, measured by sporulation levels, differs 1,000-fold when devRS+ is moved from a distance of 20 kb to 3 Mb from the mutant devRS locus. Expression of devR is also dependent on the cell density at which development is initiated, a third level of regulation. Multiple levels of regulation suggest that devRS is a switch required to activate completion of aggregation and sporulation.

Amino Acid Sequence↗
PubMed1993

Identification of esg, a genetic locus involved in cell-cell signaling during Myxococcus xanthus development.

JD258, a Tn5 insertion mutant of Myxococcus xanthus, was shown to have major defects in three development-associated properties: expression of the developmentally regulated tps gene, spore formation, and production of multicellular fruiting bodies. The defects in tps gene expression and sporulation could be substantially corrected, at the phenotypic level, by mixing JD258 with wild-type cells (extracellular complementation). By this criterion, JD258 appeared to be a new member of a group of conditional developmental mutants that were previously characterized and placed in four extracellular complementation groups (A to D) based on the ability of mutants in one group to stimulate development in mutants belonging to a different group (D. C. Hagen, A. P. Bretscher, and D. Kaiser, Dev. Biol. 64:284-296, 1978). Mutants from groups A, B, C, and D all displayed extracellular complementation activity when mixed with JD258. These results, and other aspects of the phenotype of JD258, indicate that this mutant defines a fifth extracellular complementation group, group E. The M. xanthus esg locus identified by the Tn5 insertion in JD258 was cloned in Escherichia coli and used for further genetic analysis of the locus. These studies indicated that the esg locus resides within a 2.5-kb region of the M. xanthus chromosome and that the locus contains at least two genetic complementation groups. Our results are consistent with a model in which the esg locus controls the production of a previously unrecognized extracellular signal that must be transmitted between cells for the completion of M. xanthus development.

Cell Communication↗
PubMed1993

Autophosphorylation of nucleoside diphosphate kinase from Myxococcus xanthus.

The nucleoside diphosphate kinase (NDP kinase) from Myxococcus xanthus has been purified to homogeneity and crystallized (J. Munoz-Dorado, M. Inouye, and S. Inouye, J. Biol. Chem. 265:2702-2706, 1990). In the presence of ATP, the NDP kinase was autophosphorylated. Phosphoamino acid analysis was carried out after acid and base hydrolyses of phosphorylated NDP kinase. It was found that the protein was phosphorylated not only at a histidine residue but also at a serine residue. Replacement of histidine 117 with a glutamine residue completely abolished the autophosphorylation and nucleotide-binding activity of the NDP kinase. Since histidine 117 is the only histidine residue that is conserved in all known NDP kinases so far characterized, the results suggest that the phosphohistidine intermediate is formed at this residue during the transphosphorylation reaction from nucleoside triphosphates to nucleoside diphosphates. Preliminary mutational analysis of putative ATP-binding sites is also presented.

Adenosine Triphosphate↗
PubMed1993

Cloning and nucleotide sequence of the Myxococcus xanthus lon gene: indispensability of lon for vegetative growth.

The lon gene of Escherichia coli is known to encode protease La, an ATP-dependent protease associated with cellular protein degradation. A lon gene homolog from Myxococcus xanthus, a soil bacterium which differentiates to form fruiting bodies upon nutrient starvation, was cloned and characterized by use of the lon gene of E. coli as a probe. The nucleotide sequence of the M. xanthus lon gene was determined. It contains an open reading frame that encodes a 92-kDa protein consisting of 817 amino acid residues. The deduced amino acid sequence of the M. xanthus lon gene product showed 60 and 56% identity with those of the E. coli and Bacillus brevis lon gene products, respectively. Analysis of an M. xanthus strain carrying a lon-lacZ operon fusion suggested that the lon gene is similarly expressed during vegetative growth and development in M. xanthus. In contrast to that of E. coli, the M. xanthus lon gene was shown to be essential for cell growth, since a null mutant could not be isolated.

ATP-Dependent Proteases↗
PubMed1994

Use of a phase variation-specific promoter of Myxococcus xanthus in a strategy for isolating a phase-locked mutant.

The bacterium Myxococcus xanthus alternates between two colony types distinguished by colony morphology and pigmentation. Because the two phases are interconvertible, this phenomenon has been termed phase variation. In one phase, the colonies are bright yellow, rough, and swarming. In the alternate phase, the colonies are tan and mucoid with smooth edges. During exponential vegetative growth, the populations within a colony reach an equilibrium of approximately 99% yellow and 1% tan cells. Neither the biological function nor the genetic mechanism of phase variation is currently understood. To investigate phase variation, a yellow-phase-specific promoter was identified by Tn5lac mutagenesis. A tan-phase-locked mutant was isolated by a strategy, described in this study, which involved introducing a selectable marker expressed under phase-regulated expression. This was accomplished by a fusion of the cloned yellow-phase-specific promoter to a promoterless kanamycin resistance gene. The defect in the phase-locked mutant, given the designation var-683, caused the rate of switching from the tan to yellow phase to be reduced by at least 10(3)-fold below the wild-type rate of switching. This strain will provide a stable tan population for genetic and biological analysis. Evidence is presented for the existence of a transcriptional regulator which controls the expression of phase-regulated promoters.

Cloning, Molecular↗
PubMed1994

Biochemical and structural analyses of the extracellular matrix fibrils of Myxococcus xanthus.

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.

Bacterial Adhesion↗
PubMed1994

Integral proteins of the extracellular matrix fibrils of Myxococcus xanthus.

The extracellular matrix fibrils of Myxococcus xanthus are mediators of cell-cell cohesion and as such are required for the maintenance of the social lifestyle characteristic of these prokaryotes. The fibrils have also been implicated as factors involved in contact-mediated cell interactions and in signal exchange. The fibrils are extracellular carbohydrate structures with associated proteins. All of the major proteins associated with the fibrils react with monoclonal antibody 2105 and can be removed from the fibrils only by boiling with sodium dodecyl sulfate (SDS) and beta-mercaptoethanol. For consistency with their integral association with the fibrils, we have designated this class of proteins as integral fibrillar proteins class 1 (IFP-1). IFP-1 comprises five major proteins whose molecular sizes range from 66 to 14 kDa. All of the proteins in IFP-1 have been purified from isolated fibrils by electroelution after size separation on SDS-PAGE gels. Analysis of the purified proteins suggested that the forms with different molecular sizes result from the aggregation of a single small-molecular-size subunit. Fingerprint analysis and amino acid composition profiles confirmed the identity among the different members of IFP-1. The sequence of the 31 amino-terminal amino acids of the 31-kDa form of IFP-1 (IFP-1:31) was determined. There was no significant homology to other known protein sequences. During development there is a dramatic shift in the banding pattern of IFP-1 proteins without any apparent overall loss of total protein.

Amino Acid Sequence↗
PubMed1994

Isolated fibrils rescue cohesion and development in the Dsp mutant of Myxococcus xanthus.

Extracellular fibrils are involved in cell cohesion and cell development in Myxococcus xanthus. One group of social motility mutants, Dsp, is unable to produce extracellular fibrils; these mutants also lose the abilities to cohere and to develop. Extracellular fibrils isolated from vegetative wild-type cells and added to Dsp cells fully restored the abilities of these cells to cohere and to undergo normal morphological development. The fibrils thus mimic the ability of intact, wild-type cells to carry out the same rescue. Optimal cohesion rescue by fibrils required calcium and magnesium ions, did not require protein synthesis, but was energy dependent, i.e., sodium azide and sodium cyanide blocked rescue. Cohesion rescue was also blocked by the diazo dye Congo red. Cohesion rescue is genus specific, i.e., isolated fibrils did not cause the cohesion of Pseudomonas aeruginosa, Bacillus subtilis, Proteus mirabilis, Escherichia coli, or the related myxobacterium Stigmatella aurantiaca. Developmental rescue of Dsp by isolated fibrils included aggregation, fruiting body formation, and myxospore morphogenesis. Developmental gene expression in the Dsp mutant was only partially rescued by the isolated fibrils.

Bacterial Adhesion↗
PubMed1994

Isolation and phenotypic characterization of Myxococcus xanthus mutants which are defective in sensing negative stimuli.

Myxococcus xanthus is a gram-negative gliding bacterium that exhibits a complex life cycle. Exposure of M. xanthus to chemicals like dimethyl sulfoxide (DMSO) at nondeleterious concentrations or the depletion of nutrients caused several negative responses by the cells. DMSO (> 0.1 M) or nutrient depletion triggered a repellent response: cell swarming was inhibited and FrzCD (a methyl-accepting chemotaxis protein) was demethylated; higher concentrations of DMSO (> 0.3 M) or prolonged starvation induced an additional response which involved cellular morphogenesis: DMSO caused cells to convert from rod-shaped vegetative cells to spherical, environmentally resistant "DMSO spores," and starvation induced myxospore formation in the fruiting bodies. In order to investigate the nature of these responses, we isolated a number of mutants defective in negative chemotaxis and/or sporulation. Characterization of these mutants indicated that negative chemotaxis plays an important role in colony swarming and in developmental aggregation. In addition, the results revealed some of the major interrelationships between the signal transduction pathways which respond to negative stimuli: (i) DMSO exposure and starvation were initially sensed by different systems, the neg system for DMSO and the stv system for starvation; (ii) the repellent response signals triggered by DMSO or starvation were then relayed by the frz signal transduction system; mutants defective in these responses showed altered FrzCD methylation patterns; and (iii) the morphogenesis signals in response to DMSO or starvation utilize a group of genes involved in sporulation (spo).

Bacterial Proteins↗
PubMed1994

The dsg gene of Myxococcus xanthus encodes a protein similar to translation initiation factor IF3.

The dsg mutants of Myxococcus xanthus are defective in fruiting body development and sporulation, yet they grow normally. The deduced amino acid sequence of the dsg gene product is 50 and 51% identical to the amino acid sequence of translation initiation factor IF3 of both Escherichia coli and Bacillus stearothermophilus, respectively. However, the Dsg protein has a carboxy-terminal extension of 66 amino acids, which are absent from its E. coli and B. stearothermophilus homologs. The Shine-Dalgarno sequence GGAGG and 5 bases further upstream are identical in M. xanthus and several enteric bacteria, despite the wide phylogenetic gap between these species. The infC gene, which encodes IF3 in enteric bacteria, starts with the atypical translation initiation codon AUU, which is known to be important for regulating the cellular level of IF3 in E. coli. Translation of the Dsg protein overexpressed from the M. xanthus dsg gene in E. coli cells initiates at an AUC codon, an atypical initiation codon in the AUU class. The dsg mutants DK429 and DK439 carry the same missense mutation that changes Gly-134 to Glu in a region of amino acid identity.

Amino Acid Sequence↗
PubMed1994

The Myxococcus xanthus dsg gene product performs functions of translation initiation factor IF3 in vivo.

The amino acid sequence of the Dsg protein is 50% identical to that of translation initiation factor IF3 of Escherichia coli, the product of its infC gene. Anti-E. coli IF3 antibodies cross-react with the Dsg protein. Tn5 insertion mutations in dsg are lethal. When ample nutrients are available, however, certain dsg point mutant strains grow at the same rate as wild-type cells. Under the starvation conditions that induce fruiting body development, these dsg mutants begin to aggregate but fail to develop further. The level of Dsg antigen, as a fraction of total cell protein, does not change detectably during growth and development, as expected for a factor essential for protein synthesis. The amount of IF3 protein in E. coli is known to be autoregulated at the translational level. This autoregulation is lost in an E. coli infC362 missense mutant. The dsg+ gene from Myxococcus xanthus restores normal autoregulation to the infC362 mutant strain. Dsg is distinguished from IF3 of E. coli, other enteric bacteria, and Bacillus stearothermophilus by having a C-terminal tail of 66 amino acids. Partial and complete deletion of this tail showed that it is needed for certain vegetative and developmental functions but not for viability.

Amino Acid Sequence↗
PubMed1994

Sensory adaptation during negative chemotaxis in Myxococcus xanthus.

Myxococcus xanthus exhibits many tactic movements that require the frz signal transduction system, such as colony swarming and cellular aggregation during fruiting body formation. Previously we demonstrated that the Frz proteins control the chemotactic movements of M. xanthus (W. Shi, T. Köhler, and D. R. Zusman, Mol. Microbiol. 9:601-611, 1993). However it was unclear from that study how chemotaxis might be achieved at the cellular level. In this study, we showed that M. xanthus cells not only modulate the reversal frequency of cell movement in response to repellent stimuli but also exhibit sensory adaptation in response to the continuous presence of nonsaturating repellent stimuli. The sensory adaptation behavior requires FrzF (a putative methyltransferase) and is correlated with the methylation-demethylation of FrzCD, a methyl-accepting chemotaxis protein. These results indicate that negative chemotaxis in M. xanthus is achieved by chemokinesis plus sensory adaptation in a manner analogous to that of the free-swimming enteric bacteria.

Acclimatization↗
PubMed1994

Evidence that asgB encodes a DNA-binding protein essential for growth and development of Myxococcus xanthus.

The asg mutants of Myxococcus xanthus are defective in production of extracellular A-signal, which serves as a cell density signal for fruiting-body development. The DNA sequence of asgB, one of the three asg genes, was determined. The deduced amino acid sequence of AsgB contains a DNA-binding helix-turn-helix motif near the C terminus. This putative helix-turn-helix is highly similar to the helix-turn-helix in region 4.2 of major sigma factors, which is the region that recognizes and interacts with -35 sequences of promoters. We propose that AsgB is a transcription factor that binds to DNA sequences similar to the -35 hexamer, TTGACA. Analyses of asgB RNA levels and expression of an asgB-lacZ translational fusion indicate that expression of asgB remains fairly constant during the transition from growth into early development. The mutation within the asgB480 allele was identified as an A-to-G transition that results in a threonine-to-alanine substitution in the predicted protein product. Attempts to replace the wild-type copy of asgB with a null allele failed, indicating that asgB may be essential for growth.

Amino Acid Sequence↗
PubMed1994

Cloning and characterization of the socA locus which restores development to Myxococcus xanthus C-signaling mutants.

The csgA gene produces an intercellular signal during fruiting body formation of the myxobacterium Myxococcus xanthus. Sporulating pseudorevertants were isolated to allow us to understand the mechanism by which CsgA is perceived by cells and used to regulate developmental gene expression. Two strains, LS559 and LS560, which have closely linked transposon insertions, soc-559 (formerly csp-559) and soc-560 (formerly csp-560), respectively, regained all the developmental behaviors lost by the csgA mutation including the ability to ripple, form fruiting bodies, and sporulate. The sequence analysis of the socA locus revealed that there are three putative protein-coding regions, designated socA1, socA2, and socA3. The deduced amino acid sequence of socA1 exhibits characteristics of the short-chain alcohol dehydrogenase family. The deduced amino acid sequence of socA2 shares 48% identity with the frdD gene product of the frd operon in Proteus vulgaris which anchors fumarate reductase to the membrane. The deduced amino acid sequence of socA3 does not show homology to any known proteins. Genotypic complementation, Northern (RNA) blotting, DNA sequence analysis, and the pattern of gene expression all suggest that these three genes are polycistronic. Since the socA mutations effectively bypass CsgA, the question of why csgA is maintained in M. xanthus was examined by studying the long-term stability of socA spores. Unlike the wild type, socA mutant spores germinated on starvation agar. Transmission electron micrographs of spore thin sections revealed that germination is not due to an obvious structural deficiency of the socA spores. These results suggest that the ability of socA myxospores to survive long periods under unfavorable environmental conditions is severely comprised. Therefore, soxA appears to be essential for the development of M. xanthus.

Amino Acid Sequence↗
PubMed1995

Using a phase-locked mutant of Myxococcus xanthus to study the role of phase variation in development.

The bacterium Myxococcus xanthus undergoes a primitive developmental cycle in response to nutrient deprivation. The cells aggregate to form fruiting bodies in which a portion of the cells differentiate into environmentally resistant myxospores. During the growth portion of the M. xanthus life cycle, the organism also undergoes a phase variation, in which cells alternate between yellow and tan colony-forming variants. Phase variation occurs in our laboratory strain (M102, a derivative of DK1622) at a frequency high enough that a single colony of either the yellow or the tan phase already contains cells of the alternate phase. In this study we demonstrate that tan cells within a predominantly yellow population of phase variation-proficient cells are preferentially recovered as heat- and sonication-resistant spores. To further investigate the possibility of a differential role of tan and yellow cells during development, a tan-phase-locked mutant was used to compare the developmental phenotypes of a pure tan population with a predominantly yellow, phase variation-proficient population. Pure tan-phase populations did not produce fruiting bodies or mature spores under conditions in which predominantly yellow wild-type populations did so efficiently. Pure populations of tan-phase cells responded to developmental induction by changing from vegetative rod-shaped cells to round forms but were unable to complete the maturation to heat- and sonication-resistant, refractile spores. The developmental defect of a tan-phase-locked mutant was rescued by the addition of phase variation-proficient cells from a predominantly yellow culture. In such mixtures the tan-phase-locked mutant not only completed the process of forming spores but also was again preferentially represented among the viable spores. These findings suggest the intriguing possibility that the tan-phase cells within the vegetative population entering development are the progenitors of spores and implicate a requirement for yellow-phase cells in spore maturation.

Bacterial Adhesion↗