Morphogenetic movements and multicellular development in the fruiting Myxobacterium, Stigmatella aurantiaca.

Stigmatella aurantiaca, strain DW-4, is a bacterium that grows as single cells in liquid culture but will synchronously aggregate and construct multicellular fruiting bodies when starved on an agar surface. The fruiting body consists of a stalk and several sporangia housing differentiated myxospores. Fruiting body development is stimulated by exposure of the aggregating cells to incandescent light.     

Pheromone produced by the myxobacterium Stigmatella aurantiaca.

An extracellular, diffusible signaling molecule (pheromone) was produced by Stigmatella aurantiaca during fruiting body formation. The pheromone decreased the aggregation period in both the light and the dark and substituted for light in stimulating the maturation of aggregates into fruiting bodies. The cells were more sensitive to lower concentrations of pheromone in the light than in the dark, possibly explaining the stimulation of aggregation and fruiting body formation by light. The pheromone also interacted cooperatively with GMP to shorten the aggregation period. The pheromone behaved chemically as a low-molecular-weight lipid.     

Effects of specific cations on aggregation and fruiting body morphology in the myxobacterium Stigmatella aurantiaca.

The cation requirements for fruiting body formation in the myxobacterium Stigmatella aurantiaca on agarose were determined. Calcium alone caused the cells to aggregate into interconnecting ridges. Under these conditions, stalk formation was severely depressed but sporangia frequently formed. The combination of magnesium and manganese was necessary for optimal formation of discrete aggregates (rather than ridges) and stalks. Manganese inhibited sporangium development. The inclusion of calcium into the magnesium-manganese medium overcame the inhibition by manganese and stimulated the production of multiple sporangia.     

Development of Stigmatella aurantiaca: effects of light and gene expression.

Stigmatella aurantiaca, a gliding, gram-negative bacterium, exhibits complex developmental changes upon starvation. In the light the cells aggregate and develop multicellular fruiting bodies with stalks and sporangia within 20 h. Between 23 and 27 h, sonication-resistant myxospores are synchronously formed inside the sporangia. On the other hand, in the dark, the cells aggregate and differentiate into myxospores between 13 and 27 h without forming stalks and sporangia. The pattern of protein synthesis during development in the light as well as in the dark was investigated. Three periods of synthesis, characterized by sharp increases and decreases in the rate of isotope incorporation into certain proteins, were distinguished. In the light these periods corresponded approximately to an early stage before the formation of aggregates, a middle period during which aggregates appeared and developed into fruiting bodies, and a late stage that corresponded to the appearance of myxospores. The pattern of protein synthesis in the dark could also be divided into three stages, but the middle stage was considerably shorter than in the light and showed diminished synthesis of certain proteins that were actively synthesized in the light. In particular, the synthesis of one protein was detected only in samples that developed in the light.     

Light and electron microscope studies on the fruiting bodies of Chondromyces crocatus

Summary The fruiting bodies of Chondromyces crocatus have been examined by both light and electron microscopy. The cysts are bounded by a discrete layer of dense slime enclosing a material of lesser density in which the closely packed resting cells are embedded. The latter, in contrast to the microcysts of other myxobacters, are not enclosed in individual slime capsules. Young resting cells commonly contain numerous mesosomes while older resting cells are characterized by what appear to be large lipid granules.The slime stalk consists largely of a system of vertical, parallel empty tubules through which the cells have migrated during fruiting body development.Supported by grant number A 1022 from the National Research Council of Canada.     

The developmental capacity of various stages of a macrocyst-forming strain of the cellular slime mold, Dictyostelium mucoroides.

Vegetative cells of certain strains of Dictyostelium mucoroides form fruiting bodies on an agar surface and macrocysts when placed under saline. This study sought to determine whether the aggregation and pseudoplasmodial stages of fruiting body formation could be induced to form macrocysts when placed under saline. Likewise, different stages in macrocyst formation were put on an agar surface to determine their potential to switch to fruiting body formation. It was found that 78% of the aggregates and 21% of the pseudoplasmodia placed under saline formed macrocysts indicating that as fruiting body development proceeds, there is a restriction of the capability of cells to respond to environmental conditions favoring macrocyst formation. Stages in macrocyst development prior to the formation of precysts always formed fruiting bodies when put on agar. Once precysts had formed, surrounded by their acellular sheath, they always developed as macrocysts on agar. Peripheral cells isolated from precysts and put on agar quickly aggregated; the aggregates became surounded by a sheath and developed as macrocysts. If isolated peripheral cells were allowed to proliferate on the agar surface, the resulting cells aggregated and formed fruiting bodies.     

Morphogenetic effects of light and guanine derivatives on the fruiting myxobacterium Stigmatella aurantiaca.

When low cell densities of the myxobacterium Stigmatella aurantiaca were starved on an inorganic salts and agar medium, cell aggregation and fruiting body formation showed a striking dependency upon the presence of light. This dependency was not manifested when sufficient amounts of guanosine or guanine nucleotides were added to the medium. Light interacted cooperatively with suboptimal concentrations of guanine compounds to promote development. None of the other purine or pyrimidine derivatives, with the exception of adenine, stimulated development. However, aggregates that formed in the presence of adenine did not mature into fruiting bodies and instead disaggregated.     

Cell patterning in branched and unbranched fruiting bodies of the cellular slime mold Polysphondylium pallidum

Cell patterning, the percentage of spores and stalk cells, was measured in branched and unbranched asexual fruiting bodies of Polysphondylium pallidum. Unlike D. discoideum, where small and large fruiting bodies are more stalky than average-sized fruiting bodies, the overall cell patterning was the same in branched and unbranched fruiting bodies of all sizes in P. pallidum. Light greatly increased the numbers of fruiting bodies in P. pallidum per unit area (or decreased aggregation territory size) so that most fruiting bodies formed in the light were small and unbranched. By contrast, light had little effect on the cell patterning of P. pallidum, although there was a slight increase in the percentage of stalk cells in the light compared to the dark. This indicates that the mechanisms governing light sensitivity of aggregation territory size and cell patterning have different components in P. pallidum. The accuracy of cell patterning of individual branches of branched fruiting bodies was so imprecise as to leave doubt that patterning is occurring at the branch level. Individual whorls of branched fruiting bodies had a greater percentage spores (90%) than whole fruiting bodies (78%) and the cell patterning was relatively imprecise. Only in whole fruiting bodies was the spore:stalk ratio highly correlated. These findings are consistent with cell pattern determination operating at the whole aggregate level, rather than at the individual whorl or branch level in P. pallidum.     

粘细菌生态多样性的初步研究

通过对河北,云南,青藏高原不同地区的粘细菌进行生态多样的研究,从42个样品中分离得到了10个属（Archangium,Myxococcus,Cystobacter,Corallococcus,Melittangium,Sorangium,Polyangium,Chondromyces,Angiococccus,Stigmatella)的150余株粘细菌,其中包括一些尚未有描述的菌株,有待鉴定,根据这些菌株的子实体结构,菌落形态,营养细胞,粘孢子形态等特征将它们初步鉴定到属,对这些特有自然生态环境的粘细菌按不同地点,植被,营养基质进行统计比较,结果表明,粘细菌生态分布极为广泛,具有丰富的生态多样性,以上结果为粘细菌生物资源的有效开发利用奠定了基础。     

Localization of the stress protein SP21 in indole-induced spores, fruiting bodies, and heat-shocked cells of Stigmatella aurantiaca.

The localization and distribution of the stress protein SP21 in indole-induced vegetative cells, fruiting bodies, and heat shocked cells of Stigmatella aurantiaca were determined by immunoelectron microscopy. SP21 was found at the cell periphery in heat-shocked cells and either at the cell periphery or within the cytoplasm in indole-induced cells, often concentrated in clusters. In fruiting-body-derived spores, SP21 was located mainly at the cell wall, preferentially at the outer periphery. Furthermore, SP21 antigen was associated with cellular remnants within the stalk and within the peripheral horizon next to the fruiting body.     

Autofluorescence and Ultrastructure in the Myxomycete Diachea leucopodia (Physarales)

Autofluorescence is reported for the first time in Myxomycete fruiting bodies. Ultrastructure of stalked sporangia of Diachea leucopodia (Didymiaceae, Physarales) was studied using scanning and transmission electron microscopy, energy-dispersive X-ray microanalysis, and fluorescence microscopy. External and internal properties of the peridium that surround the spores and capillitium exhibit autofluorescence. The stalk is composed of calcareous granules and energy-dispersive X-ray microanalysis demonstrates that the elemental composition of the peridium, capillitium, and stalk has varying concentrations of calcium.     

Fine Structure of Fruiting Bodies of Stigmatella aurantiaca (Myxobacterales)

The fruiting body of Stigmatella aurantiaca consists of a thick stalk supporting a number of individual cysts. The stalk is made of discontinuous tubules, of dimensions known for vegetative cells, which are oriented parallel to the longitudinal axis of the stalk. The red-brown cysts contain numerous, randomly oriented myxospores which are surrounded by thick, fibrous capsules. Their cell walls are wavy or ruffled and exhibit fewer budlike infoldings than reported for myxospores induced in liquid. We suggest that the extended time period available for metabolic and regulatory adjustments by the cell during morphogenesis within cysts accounts for the presence of considerably fewer deep cell wall infoldings than in glycerol-induced myxospores.     

Morphogenesis of Stigmatella aurantiaca fruiting bodies.

Scanning electron micrographs of intermediate stages of fruiting body formation in the myxobacterium Stigmatella aurantiaca suggest that fruiting body formation can be divided into several stages distinguishable on the basis of the motile behavior of the cells. Aggregates formed at sites where cells glide as groups in circles or spirals. Thus, each aggregate was surrounded by a wide band of cells. Several streams of cells were pointed toward and connected to the wide band of cells at the base of the aggregate, suggesting directed cell movement toward the aggregate. The pattern of cells at the base of taller, more mature aggregates suggested that groups of cells enter the aggregate from the surrounding band of cells by changing the pitch of their movement, thus creating an ascending spiral. Stalk formation was characterized by a distinctly different pattern, which suggested that single cells emerge from the band of cells and move toward the aggregate, under it, and then vertically to create the stalk. At this stage, the aggregate appeared to be torn from the substrate as it was lifted off the surface. The cells in the completed stalks were well separated, and most had their long axes pointed in a vertical direction. A great deal of the stalk material appeared to be slime in which the cells were embedded and through which they were presumably moving in the live material. Some suggestions regarding factors that may direct the observed morphogenetic movements are discussed.     

Loss of the beta-catenin homologue aardvark causes ectopic stalk formation in Dictyostelium

Aardvark (Aar) is a Dictyostelium beta-catenin homologue with both cytoskeletal and signal transduction roles during development. Here, we show that loss of aar causes a novel phenotype where multiple stalks appear during late development. Ectopic stalks are preceded by misexpression of the stalk marker ST-lacZ in the surrounding tissue. This process does not involve the kinase GSK-3. Mixing experiments show that ectopic ST-lacZ expression and stalk formation are cell non-autonomous. The protein-cellulose matrix surrounding the stalk of aar mutant fruiting bodies is defective, and damage to the stalk of wild-type fruiting bodies leads to ectopic ST-lacZ expression. We postulate that poor synthesis of the stalk tube matrix allows diffusion of a stalk cell-inducing factor into the surrounding tissue.     

Cell Patterning During Slug Migration and Early Culmination in Dictyostelium discoideum

Abstract. The effects of migration and culmination on patterning of presumptive (prespore and prestalk) cells and mature (spore and stalk) cells of D. discoideum were investigated. The ratio of prespore to total cells, as determined by staining with fluorescein-conjugated antispore globulin, was constant (77%) up until 8 h of slug migration, but then decreased to a level (64%) which thereafter remained unchanged during migration. Cells which lost prespore antigen during migration were located in the posterior (prespore) part next to the agar surface.
Upon induction of culmination, however, the ratio of prespore cells quickly increased to the normal level (77%) within 1–2 h. During the transition between migration and culmination prestalk and prespore cells were considerably intermixed within the cell mass, before the normal prestalk-prespore pattern was reestablished at the preculmination (Mexican hat) stage. Spore: stalk ratios within fruiting bodies were normal irrespective of the lengths of slug migration.     

Multicellular development in Myxococcus xanthus is stimulated by predator-prey interactions

Myxococcus xanthus is a predatory bacterium that exhibits complex social behavior. The most pronounced behavior is the aggregation of cells into raised fruiting body structures in which cells differentiate into stress-resistant spores. In the laboratory, monocultures of M. xanthus at a very high density will reproducibly induce hundreds of randomly localized fruiting bodies when exposed to low nutrient availability and a solid surface. In this report, we analyze how M. xanthus fruiting body development proceeds in a coculture with suitable prey. Our analysis indicates that when prey bacteria are provided as a nutrient source, fruiting body aggregation is more organized, such that fruiting bodies form specifically after a step-down or loss of prey availability, whereas a step-up in prey availability inhibits fruiting body formation. This localization of aggregates occurs independently of the basal nutrient levels tested, indicating that starvation is not required for this process. Analysis of early developmental signaling relA and asgD mutants indicates that they are capable of forming fruiting body aggregates in the presence of prey, demonstrating that the stringent response and A-signal production are surprisingly not required for the initiation of fruiting behavior. However, these strains are still defective in differentiating to spores. We conclude that fruiting body formation does not occur exclusively in response to starvation and propose an alternative model in which multicellular development is driven by the interactions between M. xanthus cells and their cognate prey.     

Territorial interactions between two Myxococcus Species.

It is unusual to find fruiting bodies of different myxobacteria occupying the same territory on natural samples. We were thus interested in determining whether myxobacteria establish territorial dominance and, if so, what the mechanism of that interaction is. We had previously observed that vegetative swarms of Myxococcus xanthus and Stigmatella aurantiaca placed close to each other on an agar surface initially merged but eventually separated. Further studies indicated that these two species also formed separate fruiting bodies when mixed together on developmental agar (unpublished observation). We examined the interactions between two more closely related myxobacteria, M. xanthus and M. virescens, in greater detail. When mixtures of a kanamycin-resistant strain of M. xanthus and a kanamycin-sensitive strain of M. virescens were placed together under developmental conditions, the cells sorted themselves out and established separate fruiting body territories. In addition, differential viable counts of a mixture of the two species during development indicated that each strain was producing an extracellular component that inhibited the growth and development of the other. Nevertheless, finally, M. virescens invariably outcompeted M. xanthus at all input ratios of M. xanthus/M. virescens tested. This is consistent with the observation that M. virescens is by far the more commonly encountered of the two species. The properties of the inhibitory substance from M. virescens are consistent with the possibility that it is a bacteriocin. Our working hypothesis is that the bacteriocin plays a role in the establishment of myxobacterial territoriality. If so, this is an example of an ecological function of bacteriocins.     

Synthesis of several membrane proteins during developmental aggregation in Myxococcus xanthus

We have examined the pattern of synthesis of several membrane proteins during the aggregation phase of development in Myxococcus xanthus. Development was initiated by plating vegetative cells on polycarbonate filters placed on top of an agar medium that supported fruiting body formation. At various times during aggregation a filter was removed, the cells were pulse-labeled with [35S]methionine, and the membrane proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The rate of synthesis of numerous individual proteins changed during aggregation; we concentrated on six whose pattern of synthesis was greatly altered during aggregation. The rate of synthesis of five of the six proteins increased considerably during aggregation; that of the remaining protein was curtailed and appeared to be regulated by nutrient conditions. Three of the five major membrane proteins that increased during aggregation had a unique pattern of synthesis that was displayed only under conditions that are are required for development - high cell density, nutrient depletion, and a solid (agar) surface. The remaining two proteins were not unique to development; the appearance of one protein could be induced under conditions of high cell density, whereas the other could be induced by placing the cells on a solid agar surface. All of the five major proteins that appeared during development did so during the preaggregation stage, and the synthesis of four of the five proteins appeared to be curtailed late in aggregation. The synthesis of the remaining protein continued throughout aggregation.     

The Possible Involvement of Cyclic AMP and Volatile Substance (s) in the Development of a Macrocyst-Forming Strain of Dictyostelium mucoroides

A mutant MF1 previously isolated from Dictyostelium mucoroides -7 (Dm7) formed macrocysts with or without light when plated on agar at high cell dinsities. At lower cell densities, however, the MF1 cells formed only fruiting bodies. This failure to form macrocysts was shown to be due to the subthreshfold concentration of a volatile substance(s) required for macrocyst formation. Although ammonia is a volatile substance produced by both the Dm7 and MF1 cells, no evidence of its involvement in macrocyst formation was obtained. Mixing the Dm7 and MF1 in a one-to-one ratio resulted only in fruiting body formation suggesting that the Dm7 cells produced a factor which allowed MF1 cells to form fruiting bodies. This factor may be cyclic AMP (cAMP) since addition of cAMP to the medium directed development of MF1 cells to fruiting body formation. The effect of cAMP was exhibited most conspicuously when MF1 cells were exposed at the aggregation stage. Based on these results it is suggested that developmental pathway of the D. mucoroides macrocystforming strain Dm7 and its mutant MF1 may be determined by the relative concentrations of the volatile, macrocyst-inducing substance(s) and cAMP at the aggregation stage.