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PubMed1999

Diffusion through agar blocks of finite dimensions: a theoretical analysis of three systems of practical significance in microbiology.

A number of experimental methods in biology depend on the kinetics of diffusion of a substance through a gel. This paper reviews the diffusion equations, gives the experimental limitations for some useful cases, and presents computer simulations for cases that cannot be treated analytically. While double diffusion is not considered, three single-diffusion situations are treated. (1) Systems for the study of chemotaxis in the gliding bacterium Myxococcus xanthus. Experimental designs used for this in many cases in the literature were inappropriate and mathematical analysis of these is presented. (2) The development of gradient plates. The time necessary for vertical diffusion to become substantially complete and before diffusion in the direction of the original slant has proceeded significantly is calculated. (3) The application to antimicrobial disk susceptibility tests. The basis of the measurement of antibiotic sensitivities with disks containing antimicrobial agents, as routinely used in clinical microbiological and testing laboratories, is analysed and the limitations are assessed and improvements suggested.

Agar↗
PubMed1993

Spatial restriction of cellular differentiation.

Myxococcus xanthus cells differentiate into myxospores within a fruiting body, an aggregate of approximately 10(5) cells. Previous work had discerned an inner and outer domain within the fruiting body differentiated by cell density and cell alignment. To test whether the two domains might play different roles in spore differentiation, developmentally regulated gene fusions were screened for expression restricted to one domain or the other. Transcriptional lacZ fusions to 80 developmentally regulated genes were examined and eight fusions were found that restricted expression to the inner domain, while one fusion, omega 7621, showed initial expression in the outer domain. Initial omega 7621 expression coincided with patches of spore precursors evident in bright-field microscopy. Later in development, both omega 7621 expression and the patches expanded inward, eventually filling both the inner and outer domains. Previous work had also shown that high cell density and cell alignment are required for transmission of the C-signal, which is needed to initiate spore differentiation. Evidence is presented for a novel morphogenetic mechanism in which C-signaling in the outer (high density) domain initiates spore differentiation. It is proposed that spore precursors are passively transported from the outer to the inner domain by the movements of undifferentiated rod cells. Reconstruction experiments showed that developing rod cells move with sufficient force to displace spores. Spore precursors thus accumulate in the inner domain where they express spore-specific genes at high levels and account for inner domain specific expression.

Biological Transport↗
PubMed2003

Interplay of chemotaxis and chemokinesis mechanisms in bacterial dynamics.

Motivated by observations of the dynamics of Myxococcus xanthus, we present a self-interacting random walk model that describes the competition between chemokinesis and chemotaxis. Cells are constrained to move in one dimension, but release a chemical chemoattractant at a steady state. The bacteria sense the chemical that they produce. The probability of direction reversals is modeled as a function of both the absolute level of chemoattractant sensed directly under each cell as well as the gradient sensed across the length of the cell. If the chemical does not degrade or diffuse rapidly, the one-dimensional trajectory depends on the entire past history of the trajectory. We derive the corresponding Fokker-Planck equations, use an iterative mean-field approach that we solve numerically for short times, and perform extensive Monte Carlo simulations of the model. Cell positional distributions and the associated moments are computed in this feedback system. Average drift and mean squared displacements are found. Crossover behaviors among different diffusion regimes are found.

Bacterial Physiological Phenomena↗
PubMed2005

A novel bacterial signalling system with a combination of a Ser/Thr kinase cascade and a His/Asp two-component system.

Prokaryotes and eukaryotes have long been thought to use very different types of kinases (the His kinases of the 'bacterial' two-component systems versus the 'eukaryotic' Ser/Thr/Tyr kinases) to carry out signal transduction. This paradigm no longer holds true, because both systems are now found together in an increasing number of prokaryotic organisms and 'two-component' His kinase are present in eukaryotes. Pioneering work on bacterial protein serine threonine kinases (PSTKs) has been performed in Myxococcus xanthus, a soil bacterium with a complex life cycle that possesses orthologues of signalling-related kinases 'typical' of both the prokaryotic and the eukaryotic kingdoms. In the work reported in this volume of Molecular Microbiology, Nariya and Inouye describe a PSTK cascade that modulates the biochemical activity of MrpC, a CRP-like transcriptional regulator for essential developmental signalling pathways in M. xanthus whose transcription is under the control of a two-component system. This is the first report of both a functional PSTK cascade in bacteria and the use of both PSTK and two-component systems to control a single complex bacterial signalling event.

Aspartate Kinase↗
PubMed2006

Secretins take shape.

Secretins are a unique class of bacterial multimeric outer membrane proteins that probably differ considerably from other, less complex outer membrane proteins in their overall structure and organization, and in their requirements for outer membrane targeting and assembly factors. In this MicroCommentary, we discuss these differences with respect to the role of a specific class of lipoproteins, often referred to as pilotins, in secretin complex assembly. We compare them with other lipoproteins that play a role in Omp85/YaeT-mediated assembly of more classical outer membrane proteins. One of the examples we have chosen is the Myxococcus Xanthus lipoprotein Tgl. Coculture of cells with and without Tgl allows secretin assembly (and, hence, type IV pilus assembly) in the cells without Tgl, indicating that it can act by cell-to-cell contact or can transfer between cells.

Bacterial Outer Membrane Proteins↗
PubMed2006

Phospholipid directed motility of surface-motile bacteria.

Myxococcus xanthus is a surface-motile bacterium that has adapted at least one chemosensory system to allow directed movement towards the slowly diffusible lipid phosphatidylethanolamine (PE). The Dif chemosensory pathway is remarkable because it has at least three inputs coupled to outputs that control extracellular matrix (ECM) production and lipid chemotaxis. The methyl-accepting chemotaxis protein, DifA, has two different sensor inputs that have been localized by mutagenesis. The Dif chemosensory pathway employs a novel protein that slows adaptation. Lipid chemotaxis may play important roles in the M. xanthus life cycle where prey-specific and development-specific attractants have been identified. Lipid chemotaxis may also be an important mechanism for locating nutrients by lung pathogens such as Pseudomonas aeruginosa.

Bacterial Proteins↗
PubMed2006

Gliding motility and polarized slime secretion.

Myxococcus leaves a trail of slime on agar as it moves. A filament of slime can be seen attached to the end of a cell, but it is seen only at one end at any particular moment. To identify genes essential for A motility, transposon insertion mutations with defective A motility were studied. Fifteen of the 33 mutants had totally lost A motility. All these mutant cells had filaments of slime emerging from both ends, indicating that bipolar secretion prevents A motility. The remaining 18 A motility mutants, also produced by gene knockout, secreted slime only from one pole, but they swarmed at a lower rate than A(+) and are called 'partial' gliding mutants, or pgl. For each pgl mutant, the reduction in swarm expansion rate was directly proportional to the reduction in the coefficient of elasticotaxis. The pgl mutants have a normal reversal frequency and normal gliding speed when they move. But their probability of movement per unit time is lower than pgl(+) cells. Many of the pgl mutants are produced by transposon insertions in glycosyltransferase genes. It is proposed that these glycosyltransferases carry out the synthesis of a repeat unit polysaccharide that constitutes the slime.

Bacterial Proteins↗
PubMed1993

Isoprenoid biosynthesis in bacteria: two different pathways?

The biosynthesis of isopentenylpyrophosphate, a central intermediate of isoprenoid formation, was investigated in six different bacterial organisms. Cell-free extracts of Myxococcus fulvus, Staphylococcus carnosus, Lactobacillus plantarum and Halobacterium cutirubrum converted [14C]acetyl-CoA or [14C]hydroxymethylglutaryl-CoA to [14C]mevalonic acid. Furthermore, [14C]mevalonic acid, [14C]mevalonate-5-phosphate and [14C]mevalonate-5-pyrophosphate were metabolized to [14C]isopentenylpyrophosphate. These data demonstrated the in vitro operation of acetoacetate pathway for the formation of isopentenylpyrophosphate in bacteria. In contrast, no intermediates of this reaction sequence could be detected using cell-free extracts of Zymomonas mobilis and Escherichia coli. These results indicate that at least two different pathways for the biosynthesis of isopentenylpyrophosphate are present in bacteria.

Acetyl Coenzyme A↗
PubMed1999

Conservation of the pyrrolnitrin biosynthetic gene cluster among six pyrrolnitrin-producing strains.

The prnABCD gene cluster from Pseudomonas fluorescens encodes the biosynthetic pathway for pyrrolnitrin, a secondary metabolite derived from tryptophan which has strong anti-fungal activity. We used the prn genes from P. fluorescens strain BL915 as a probe to clone and sequence homologous genes from three other Pseudomonas strains, Burkholderia cepacia and Myxococcus fulvus. With the exception of the prnA gene from M. fulvus59% similar among the strains, indicating that the biochemical pathway for pyrrolnitrin biosynthesis is highly conserved. The prnA gene from M. fulvus is about 45% similar to prnA from the other strains and contains regions which are highly conserved among all six strains.

Antifungal Agents↗
PubMed2005

Cell-to-cell transfer of bacterial outer membrane lipoproteins.

Myxococcus xanthus cells can glide forward by retracting type IV pili. Tgl, an outer membrane lipoprotein, is necessary to assemble pili. Tgl mutants can be transiently "stimulated" if brought into end-to-end contact with tgl+ donor cells. By separating the stimulated recipient cells from donor cells, we found that Tgl protein was transferred from the donors to the rescued recipient cells. Mutants lacking CglB lipoprotein, which is part of a second gliding engine, could also be stimulated, and CglB protein was transferred from donor to recipient cells. The high transfer efficiency of Tgl and CglB proteins suggests that donor and recipient cells briefly fuse their outer membranes.

Antigens, Bacterial↗
PubMed1992

Cell surface modifications induced by calcium ion in the myxobacterium Stigmatella aurantiaca.

Calcium ion induces in the myxobacterium Stigmatella aurantiaca the ability to glide on solid surfaces and to become cohesive (D. F. Gilmore and D. White, J. Bacteriol. 161:113-117, 1985; B. J. Womack, D. F. Gilmore, and D. White, J. Bacteriol. 171:6093-6096, 1989). The addition of calcium ion to the growth medium resulted in the formation of extracellular fibrils, the appearance in the membrane fractions of a 30-kDa protein, and the accumulation in a low-speed centrifugal pellet of 10 polypeptides that cross-reacted with affinity-purified antibody to one of the polypeptides. One of the polypeptides, a 55-kDa protein, was present in the membrane fraction of control cells not incubated with calcium ion and was apparently translocated to the extracellular matrix during incubation in medium containing calcium ion. The 55-kDa protein was immunologically related to a 65-kDa protein located on the fibrils of another myxobacterium, Myxococcus xanthus.

Bacterial Proteins↗
PubMed1996

Use of PCR to isolate genes encoding sigma54-dependent activators from diverse bacteria.

Degenerate PCR probes were used to amplify gene fragments encoding the catalytic domain of sigma54-dependent transcription activators. The procedure should be widely applicable, as it recovered both known and novel gene fragments: 5 from Rhizobium meliloti, 13 from Myxococcus xanthus, and 3 from Bacillus subtilis. No fragments were obtained from Synechococcus sp. strain PCC 7002 or Saccharomyces cerevisiae.

Amino Acid Sequence↗
PubMed1962

Antibiotic activity of myxobacteria in relation to their bacteriolytic capacity.

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.

Anti-Bacterial Agents↗
PubMed2001

Bacterial gliding motility: multiple mechanisms for cell movement over surfaces.

The mechanisms responsible for bacterial gliding motility have been a mystery for almost 200 years. Gliding bacteria move actively over surfaces by a process that does not involve flagella. Gliding bacteria are phylogenetically diverse and are abundant in many environments. Recent results indicate that more than one mechanism is needed to explain all forms of bacterial gliding motility. Myxococcus xanthus "social gliding motility" and Synechocystis gliding are similar to bacterial "twitching motility" and rely on type IV pilus extension and retraction for cell movement. In contrast, gliding of filamentous cyanobacteria, mycoplasmas, members of the Cytophaga-Flavobacterium group, and "adventurous gliding" of M. xanthus do not appear to involve pili. The mechanisms of movement employed by these bacteria are still a matter of speculation. Genetic, biochemical, ultrastructural, and behavioral studies are providing insight into the machineries employed by these diverse bacteria that enable them to glide over surfaces.

Bacterial Physiological Phenomena↗
PubMed2004

Signaling in myxobacteria.

Myxobacteria use soluble and cell-contact signals during their starvation-induced formation of fruiting bodies. These signals coordinate developmental gene expression with the cell movements that build fruiting bodies. Early in development, the quorum-sensing A-signal in Myxococcus xanthus helps to assess starvation and induce the first stage of aggregation. Later, the morphogenetic C-signal helps to pattern cell movement and shape the fruiting body. C-signal is a 17-kDa cell surface protein that signals by contact between the ends of two cells. The number of C-signal molecules per cell rises 100-fold from the beginning of fruiting body development to the end, when spores are formed. Traveling waves, streams, and sporulation have increasing thresholds for C-signal activity, and this progression ensures that spores form inside fruiting bodies.

Myxococcus xanthus↗
PubMed2005

Exploitative and hierarchical antagonism in a cooperative bacterium.

Social organisms that cooperate with some members of their own species, such as close relatives, may fail to cooperate with other genotypes of the same species. Such noncooperation may take the form of outright antagonism or social exploitation. Myxococcus xanthus is a highly social prokaryote that cooperatively develops into spore-bearing, multicellular fruiting bodies in response to starvation. Here we have characterized the nature of social interactions among nine developmentally proficient strains of M. xanthus isolated from spatially distant locations. Strains were competed against one another in all possible pairwise combinations during starvation-induced development. In most pairings, at least one competitor exhibited strong antagonism toward its partner and a majority of mixes showed bidirectional antagonism that decreased total spore production, even to the point of driving whole populations to extinction. Differential response to mixing was the primary determinant of competitive superiority rather than the sporulation efficiencies of unmixed populations. In some competitive pairings, the dominant partner sporulated more efficiently in mixed populations than in clonal isolation. This finding represents a novel form of exploitation in bacteria carried out by socially competent genotypes and is the first documentation of social exploitation among natural bacterial isolates. Patterns of antagonistic superiority among these strains form a highly linear dominance hierarchy. At least some competition pairs construct chimeric, rather than segregated, fruiting bodies. The cooperative prokaryote M. xanthus has diverged into a large number of distinct social types that cooperate with clone-mates but exhibit intense antagonism toward distinct social types of the same species. Most lengthy migration events in nature may thus result in strong antagonism between migratory and resident populations, and this antagonism may have large effects on local population sizes and dynamics. Intense mutual antagonism appears to be more prevalent in this prokaryotic social species than has been observed in the eukaryotic social slime mold Dictyostelium discoideum, which also exhibits multicellular development. The finding of several cases of facultative social exploitation among these natural isolates suggests that such exploitation may occur frequently in nature in many prokaryotes with cooperative traits.

Animals↗
PubMed1992

A new bioactive molecule for improving vascular graft patency: exploratory trials in dogs.

Myxalin is a new bioactive molecule that we have isolated from the culture medium of Myxococcus xanthus, a non-pathogenic Gram negative bacterium. This glycopeptide possesses an antithrombotic effect in vivo and has been shown to promote human endothelial cell growth in vitro. With the object of exploring its ability to improve vascular graft healing and patency, myxalin was immobilized on 6 mm diameter knitted polyester prostheses using gelatin as a carrier, and the prosthesis was then implanted as an infrarenal abdominal arterial substitute in dogs for a period of 2 weeks. Two additional series of implantations were conducted for control purposes: one with gelatin-coated prostheses without myxalin, the other following normal preclotting of the polyester grafts. In order to select adequate sterilization conditions which can preserve the biological activity of myxalin, the prostheses were sterilized according to 3 different sterilization processes (gamma radiation and ethylene oxide either at 63 degrees C or 37 degrees C). At the sacrifice, all grafts were patent. The myxalin treated prostheses exhibited improved blood compatibility in terms of fewer thrombotic deposits and significant inhibition of platelet and fibrinogen uptake on their luminal surfaces. In addition, the development of a thin collagenous internal capsule with endothelial cells secreting high levels of prostacyclin was observed at both anastomoses of the myxalin-treated grafts sterilized by gamma radiation.

6-Ketoprostaglandin F1 alpha↗
PubMed1996

Sequence and analysis of a 33 kb fragment from the right arm of chromosome XV of the yeast Saccharomyces cerevisiae.

We have determined the nucleotide sequence of a cosmid (pEOA423) from chromosome XV of Saccharomyces cerevisiae. Analysis of the 33,173 bp sequence reveals the presence of 20 putative open reading frames (ORFs). Five of them correspond to previously known genes (MGM1, STE4, CDC44, STE13, RPB8). The previously published nucleotide sequences are in perfect agreement with our sequence except for STE4 and MGM1. In the latter case, 59 amino acids were truncated from the published protein at its N-terminal end due to a frameshift. The putative translation products of six other ORFs exhibit significant homology with protein sequences in public databases: O50 03 and O50 17 products are homologs of the ANC1 and MIP1 proteins of S. cerevisiae, respectively; O50 05 product is similar to that of a protein of unknown function from Myxococcus xanthus; O50 12 product is probably a new ATP/ADP carrier; O50 13 product shows homology with group II tRNA synthetases; and the O50 16 product exhibits strong similarity with the N-terminal domain of the NifU proteins from several prokaryotes. The remaining nine ORFs show no significant similarity. Among these, two contiguous ORFs (O50 19 and O50 20) are very similar to each other, suggesting an ancient tandem duplication.

Amino Acid Sequence↗