RESUMO
In response to pathogen infection, gasdermin (GSDM) proteins form membrane pores that induce a host cell death process called pyroptosis1-3. Studies of human and mouse GSDM pores have revealed the functions and architectures of assemblies comprising 24 to 33 protomers4-9, but the mechanism and evolutionary origin of membrane targeting and GSDM pore formation remain unknown. Here we determine a structure of a bacterial GSDM (bGSDM) pore and define a conserved mechanism of pore assembly. Engineering a panel of bGSDMs for site-specific proteolytic activation, we demonstrate that diverse bGSDMs form distinct pore sizes that range from smaller mammalian-like assemblies to exceptionally large pores containing more than 50 protomers. We determine a cryo-electron microscopy structure of a Vitiosangium bGSDM in an active 'slinky'-like oligomeric conformation and analyse bGSDM pores in a native lipid environment to create an atomic-level model of a full 52-mer bGSDM pore. Combining our structural analysis with molecular dynamics simulations and cellular assays, our results support a stepwise model of GSDM pore assembly and suggest that a covalently bound palmitoyl can leave a hydrophobic sheath and insert into the membrane before formation of the membrane-spanning ß-strand regions. These results reveal the diversity of GSDM pores found in nature and explain the function of an ancient post-translational modification in enabling programmed host cell death.
Assuntos
Gasderminas , Myxococcales , Microscopia Crioeletrônica , Gasderminas/química , Gasderminas/metabolismo , Gasderminas/ultraestrutura , Interações Hidrofóbicas e Hidrofílicas , Lipídeos de Membrana/química , Lipídeos de Membrana/metabolismo , Simulação de Dinâmica Molecular , Myxococcales/química , Myxococcales/citologia , Myxococcales/ultraestrutura , Estrutura Quaternária de Proteína , Subunidades Proteicas/química , Subunidades Proteicas/metabolismo , Proteólise , PiroptoseRESUMO
In recent years, extracellular vesicles (EVs) and outer membrane vesicles (OMVs) have become an extensive and diverse field of research. They hold potential as diagnostic markers, therapeutics and for fundamental biological understanding. Despite ongoing studies, numerous information regarding function, content and stability of EVs remains unclear. If EVs and OMVs ought to be used as therapeutics and in clinical environments, their stability is one of the most important factors to be considered. Especially for formulation development, EVs and OMVs need to be stable at higher temperatures. To the best of our knowledge, very little work has been published regarding heat stability of neither EVs nor OMVs. In the present study, we investigated B lymphoblastoid cell-derived EVs and OMVs derived from myxobacterial species Sorangiineae as model vesicles. We exposed the vesicles to 37 °C, 50 °C, 70 °C and 100 °C for 1 h, 6 h and 24 h, and also autoclaved them. Interestingly, physico-chemical analyses such as size, particle concentration and protein concentration showed minor alterations, particularly at 37 °C. Flow cytometry analysis emphasised these results suggesting that after heat impact, EVs and OMVs were still able to be taken up by macrophage-like dTHP-1 cells. These data indicate that both mammalian and bacterial vesicles show intrinsic stability at physiological temperature. Our findings are important to consider for vesicle formulation and for advanced bioengineering approaches.
Assuntos
Membrana Externa Bacteriana/química , Bioengenharia , Vesículas Extracelulares/química , Temperatura Alta/efeitos adversos , Membrana Externa Bacteriana/ultraestrutura , Linhagem Celular , Microscopia Crioeletrônica , Vesículas Extracelulares/ultraestrutura , Humanos , Linfócitos/citologia , Myxococcales/citologiaRESUMO
For decades, myxobacteria have been spotlighted as exemplars of social "wolf-pack" predation, communally secreting antimicrobial substances into the shared public milieu. This behavior has been described as cooperative, becoming more efficient if performed by more cells. However, laboratory evidence for cooperativity is limited and of little relevance to predation in a natural setting. In contrast, there is accumulating evidence for predatory mechanisms promoting "selfish" behavior during predation, which together with conflicting definitions of cooperativity, casts doubt on whether microbial "wolf-pack" predation really is cooperative. Here, it is hypothesized that public-goods-mediated predation is not cooperative, and it is argued that a holistic model of microbial predation is needed, accounting for predator and prey relatedness, social phenotypes, spatial organization, activity/specificity/transport of secreted toxins, and prey resistance mechanisms. Filling such gaps in our knowledge is vital if the evolutionary benefits of potentially costly microbial behaviors mediated by public goods are to be properly understood.
Assuntos
Antibacterianos/metabolismo , Myxococcales/citologia , Evolução Biológica , Modelos Biológicos , Fatores de TempoRESUMO
BACKGROUND: An efficient signal transduction system allows a bacterium to sense environmental cues and then to respond positively or negatively to those signals; this process is referred to as taxis. In addition to external cues, the internal metabolic state of any bacterium plays a major role in determining its ability to reside and thrive in its current environment. Similar to external signaling molecules, cytoplasmic signals are also sensed by methyl-accepting chemotaxis proteins (MCPs) via diverse ligand binding domains. Myxobacteria are complex soil-dwelling social microbes that can perform a variety of physiologic and metabolic activities ranging from gliding motility, sporulation, biofilm formation, carotenoid and secondary metabolite biosynthesis, predation, and slime secretion. To live such complex lifestyles, they have evolved efficient signal transduction systems with numerous one- and two-component regulatory system along with a large array of chemosensory systems to perceive and integrate both external and internal cues. RESULTS: Here we report the in silico characterization of a putative energy taxis cluster, Cc-5, which is present in only one amongst 34 known and sequenced myxobacterial genomes, Corallococcus coralloides. In addition, we propose that this energy taxis cluster is involved in oxygen sensing, suggesting that C. coralloides can sense (either directly or indirectly) and then respond to changing concentrations of molecular oxygen. CONCLUSIONS: This hypothesis is based on the presence of a unique MCP encoded in this gene cluster that contains two different oxygen-binding sensor domains, PAS and globin. In addition, the two monooxygenases encoded in this cluster may contribute to aerobic respiration via ubiquinone biosynthesis, which is part of the cytochrome bc1 complex. Finally, we suggest that this cluster was acquired from Actinobacteria, Gammaproteobacteria or Cyanobacteria. Overall, this in silico study has identified a potentially innovative and evolved mechanism of energy taxis in only one of the myxobacteria, C. coralloides.
Assuntos
Quimiotaxia/genética , Simulação por Computador , Myxococcales/genética , Myxococcales/metabolismo , Citoplasma/genética , Evolução Molecular , Genoma Bacteriano/genética , Genômica , Myxococcales/citologiaRESUMO
The transition to multicellularity, recognized as one the major transitions in evolution, has occurred independently several times. While multicellular development has been extensively studied in zygotic organisms including plant and animal groups, just a few aggregative multicellular organisms have been employed as model organisms for the study of multicellularity. Studying different evolutionary origins and modes of multicellularity enables comparative analyses that can help identifying lineage-specific aspects of multicellular evolution and generic factors and mechanisms involved in the transition to multicellularity. Among aggregative multicellular organisms, myxobacteria are a valuable system to explore the particularities that aggregation confers to the evolution of multicellularity and mechanisms shared with clonal organisms. Moreover, myxobacteria species develop fruiting bodies displaying a range of morphological diversity. In this review, we aim to synthesize diverse lines of evidence regarding myxobacteria development and discuss them in the context of Evo-Devo concepts and approaches. First, we briefly describe the developmental processes in myxobacteria, present an updated comparative analysis of the genes involved in their developmental processes and discuss these and other lines of evidence in terms of co-option and developmental system drift, two concepts key to Evo-Devo studies. Next, as has been suggested from Evo-Devo approaches, we discuss how broad comparative studies and integration of diverse genetic, physicochemical, and environmental factors into experimental and theoretical models can further our understanding of myxobacterial development, phenotypic variation, and evolution.
Assuntos
Evolução Biológica , Biologia do Desenvolvimento , Regulação Bacteriana da Expressão Gênica/fisiologia , Myxococcales/citologia , Myxococcales/genéticaRESUMO
We study mechanisms for wavenumber selection in a minimal model for run-and-tumble dynamics. We show that nonlinearity in tumbling rates induces the existence of a plethora of traveling- and standing-wave patterns, as well as a subtle selection mechanism for the wavenumbers of spatio-temporally periodic waves. We comment on possible implications for rippling patterns observed in colonies of myxobacteria.
Assuntos
Modelos Biológicos , Simulação por Computador , Cinética , Modelos Lineares , Conceitos Matemáticos , Movimento/fisiologia , Myxococcales/citologia , Myxococcales/fisiologia , Dinâmica não LinearRESUMO
Bacterial microcompartments (BMCs) are proteinaceous organelles widespread among bacterial phyla. They compartmentalize enzymes within a selectively permeable shell and play important roles in CO2 fixation, pathogenesis, and microbial ecology. Here, we combine X-ray crystallography and high-speed atomic force microscopy to characterize, at molecular resolution, the structure and dynamics of BMC shell facet assembly. Our results show that preformed hexamers assemble into uniformly oriented shell layers, a single hexamer thick. We also observe the dynamic process of shell facet assembly. Shell hexamers can dissociate from and incorporate into assembled sheets, indicating a flexible intermolecular interaction. Furthermore, we demonstrate that the self-assembly and dynamics of shell proteins are governed by specific contacts at the interfaces of shell proteins. Our study provides novel insights into the formation, interactions, and dynamics of BMC shell facets, which are essential for the design and engineering of self-assembled biological nanoreactors and scaffolds based on BMC architectures.
Assuntos
Proteínas de Bactérias/ultraestrutura , Microscopia de Força Atômica/métodos , Myxococcales/citologia , Proteínas de Bactérias/análise , Proteínas de Bactérias/genética , Cristalografia por Raios X , Myxococcales/genética , Myxococcales/ultraestrutura , Mutação Puntual , Conformação ProteicaRESUMO
OBJECTIVE: Purpose of this work was to screen myxobacteria from soils and study their biological activities towards pathogenic bacteria, tumor cells and insects. METHODS: Through inactivated E. coli and filter paper inducing methods, we isolated and purified myxobacteria from soil samples. Then we identified these purified strains based on morphological observation, physiological and biochemical characteristics, and the 16S rDNA sequences homologous analysis. By plate diffusion experiments, oral toxicity tests and tetrazolium assays, we investigated the biological activities of the myxobacterial culture supernatant. RESULTS: We isolated 35 myxobacterial strains and classified them as 4 genera: Myxococcus (9), Corallococcus (9), Nannocystis (11) and Sorangium (6). Eight purified myxobacteria were identified and named. Cytotoxicity tests show that strain C. macrospores S22 had potent and broad-spectrum cytotoxic effect on tumor cell lines including B16, 4T1, HeLa and HCT-116, so did the strains M. fulvus S51, C. exiguus S22 and M. Xanthus S55. Additionally, C. macrospores S22 also shows inhibitory activity to pathogenic bacteria Bacillus subtillis and Candida albicans. CONCLUSION: Myxobacteria are widely distributed in natural soils. C. macrosporus has potent toxicity against cancer cells and pathogenic bacteria; and C. exiguus with antitumor activity. The myxobacterial strains are promising resources for discovery and development of new active natural products and drugs.
Assuntos
Myxococcales/isolamento & purificação , Microbiologia do Solo , Animais , Linhagem Celular Tumoral , Humanos , Camundongos , Myxococcales/classificação , Myxococcales/citologia , Myxococcales/fisiologia , Neoplasias/terapia , FilogeniaRESUMO
Ten species of the order Myxococcales with validly published names are devoid of living type strains. Four species of the genus Chondromyces are represented by dead herbarium samples as the type material. For a species of the genus Melittangium and two species of the genus Polyangium, no physical type material was assigned at the time of validation of the names or later on. In accordance with rule 18f of the International Code of Nomenclature of Bacteria the following type strains are designated for these species: strain Cm a14(T) (â=âDSM 14605(T)â=âJCM 12615(T)) as the type strain of Chondromyces apiculatus, strain Cm c5(T) (â=âDSM 14714(T)â=âJCM 12616(T)) as the type strain of Chondromyces crocatus, strain Sy t2(T) (â=âDSM 14631(T)â=âJCM 12617(T)) as the type strain of Chondromyces lanuginosus, strain Cm p51(T) (â=âDSM 14607(T)â=âJCM 12618(T)) as the type strain of Chondromyces pediculatus, strain Me b8(T) (â=âDSM 14713(T)â=âJCM 12633(T)) as the type strain of Melittangium boletus, strain Pl s12(T) (â=âDSM 14670(T)â=âJCM 12637(T)) as the type strain of Polyangium sorediatum and strain Pl sm5(T) (â=âDSM 14734(T)â=âJCM 12638(T)) as the type strain of Polyangium spumosum. Furthermore, the type strains given for three species of the genera Cystobacter and Polyangium had been kept at one university institute and have been lost according to our investigations. In accordance with Rule 18c of the Bacteriological Code, we propose the following neotype strains: strain Cb fe18 (â=âDSM 14716 â=âJCM 12624) as the neotype strain of Cystobacter ferrugineus, strain Cb m2 (â=âDSM 14751â=âJCM 12627) as the neotype strain of Cystobacter minus and strain Pl fu5 (â=âDSM 14668â=âJCM 12636) as the neotype strain of Polyangium fumosum. The proposals of the strains are based on the descriptions and strain proposals given in the respective chapters of Bergey's Manual of Systematic Bacteriology (2005).
Assuntos
Myxococcales/classificação , Filogenia , Técnicas de Tipagem Bacteriana , DNA Bacteriano/genética , Myxococcales/citologia , Myxococcales/genética , Análise de Sequência de DNARESUMO
When colonizing surfaces, many bacteria are able to self-organize into an actively expanding biofilm, in which millions of cells move smoothly and orderly at high densities. This phenomenon is known as bacterial swarming. Despite the apparent resemblance to patterns seen in liquid crystals, the dynamics of bacterial swarming cannot be explained by theories derived from equilibrium statistical mechanics. To understand how bacteria swarm, a central question is how order emerges in dense and initially disorganized populations of bacterial cells. Here we briefly review recent efforts, with integrated computational and experimental approaches, in addressing this question.
Assuntos
Myxococcales/citologia , Biofilmes , Movimento , Myxococcales/fisiologiaRESUMO
Myxobacteria are social bacteria that exhibit a complex life cycle culminating in the development of multicellular fruiting bodies. The alignment of rod-shaped myxobacteria cells within populations is crucial for development to proceed. It has been suggested that myxobacteria align due to mechanical interactions between gliding cells and that cell flexibility facilitates reorientation of cells upon mechanical contact. However, these suggestions have not been based on experimental or theoretical evidence. Here we created a computational mass-spring model of a flexible rod-shaped cell that glides on a substratum periodically reversing direction. The model was formulated in terms of experimentally measurable mechanical parameters, such as engine force, bending stiffness, and drag coefficient. We investigated how cell flexibility and motility engine type affected the pattern of cell gliding and the alignment of a population of 500 mechanically interacting cells. It was found that a flexible cell powered by engine force at the rear of the cell, as suggested by the slime extrusion hypothesis for myxobacteria motility engine, would not be able to glide in the direction of its long axis. A population of rigid reversing cells could indeed align due to mechanical interactions between cells, but cell flexibility impaired the alignment.
Assuntos
Modelos Biológicos , Myxococcales/citologia , Contagem de Colônia Microbiana , Simulação por Computador , Myxococcales/crescimento & desenvolvimento , Fatores de TempoRESUMO
Three myxobacterial strains, designated SWB004, SWB005 and SWB006, were obtained from beach sand samples from the Pacific Ocean and the North Sea. The strains were cultivated in salt water containing media and subjected to studies to determine their taxonomic status, the presence of genes for the biosynthesis of polyketides and antibiotic production. 16S rDNA sequence analysis revealed the type strain Enhygromyxa salina SHK-1(T) as their closest homolog, displaying between 98% (SWB005) and 99% (SWB004 and SWB006) sequence similarity. All isolates were rod-shaped cells showing gliding motility and fruiting body formation as is known for myxobacteria. They required NaCl for growth, with an optimum concentration of around 2% [w/v]. The G + C-content of genomic DNA ranged from 63.0 to 67.3 mol%. Further, the strains were analyzed for their potential to produce polyketide-type structures. PCR amplified ketosynthase-like gene fragments from all three isolates enhances the assumption that these bacteria produce polyketides. SWB005 was shown to produce metabolites with prominent antibacterial activity, including activity towards methicillin resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis (MRSE).
Assuntos
Antibacterianos/biossíntese , Genes Bacterianos , Sedimentos Geológicos/microbiologia , Myxococcales/isolamento & purificação , Myxococcales/fisiologia , Antibacterianos/farmacologia , Composição de Bases , DNA Bacteriano/análise , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/genética , Myxococcales/citologia , Myxococcales/genética , Fenótipo , Filogenia , Tolerância ao Sal , Água do Mar/microbiologia , Análise de Sequência de DNA , Cloreto de SódioRESUMO
Interruption of the (p)ppGpp synthetase gene (rel) of Sorangium cellulosum So ce56 resulted in loss of ppGpp accumulation after norvaline treatment during exponential growth phase. The rel mutant failed to produce wild-type levels of the polyketides chivosazol and etnangien in production media. In wild-type cells expression of the chivosazol biosynthetic operon can be significantly increased by norvaline or alpha-methylglucoside. This induction does not occur in the rel mutant. The rel mutant also lost the capability to form multicellular fruiting bodies under nutrient starvation.
Assuntos
Proteínas de Bactérias/metabolismo , Ligases/metabolismo , Mutação , Myxococcales/enzimologia , Myxococcales/genética , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Teste de Complementação Genética , Guanosina Pentafosfato/metabolismo , Ligases/química , Ligases/genética , Macrolídeos/metabolismo , Myxococcales/citologia , Myxococcales/fisiologia , Estrutura Terciária de Proteína , Transcrição GênicaRESUMO
Myxobacteria are proficient producers of biologically active secondary metabolites. However, efforts to exploit these natural products for the development of new therapeutics and agrochemicals are frequently hampered by low production levels. We describe here a transposon-based strategy to identify genes encoding regulators of secondary metabolite biosynthesis in the myxobacterium Angiococcus disciformis An d48, which produces the highly efficient electron transport inhibitor myxothiazol. Extracts from 1200 transposon mutants were analyzed by HPLC, leading to the identification of six mutants in which myxothiazol production was increased by as much as 30-fold. Identifying the sites of integration coupled with sequencing of flanking regions, showed that some of the inactivated genes encode proteins with similarity to known bacterial regulators such as two-component systems and serine-threonine protein kinases. However, other gene products do not resemble any characterized proteins. Taken together, these data show that this transposon-based strategy is a valuable tool to identify regulatory genes of secondary metabolism, including gene loci which cannot be detected using current in silico approaches.
Assuntos
Biotecnologia/métodos , Elementos de DNA Transponíveis , Myxococcales/citologia , Myxococcales/metabolismo , Cromatografia Líquida de Alta Pressão , Genes Bacterianos , Metacrilatos/metabolismo , Mutação/genética , Myxococcales/genética , Fenótipo , Espectrofotometria Ultravioleta , Tiazóis/metabolismoRESUMO
Production of extracellular epothilone B, one of the potent anticancer agents, by free and immobilized Sorangium cellulosum was studied using the repeated batch culture process. The concentration of alginate used in immobilization was directly related to the mass transfer rate of nutrients, mechanical stability, and the epothilone B production yield. With the optimized 3% (w/v) calcium alginate carrier, a prolonged repeated batch culture was investigated for the 5 repeated batches for 24 days. The maximum productivity of epothilone B obtained from the alginate-immobilized cells was 5.03 mg/l/day, which is 3 times higher than that of free cells (1.68 mg/l/day).
Assuntos
Antineoplásicos/síntese química , Células Imobilizadas/metabolismo , Epotilonas/biossíntese , Myxococcales/citologia , Myxococcales/metabolismo , Alginatos/química , Alginatos/ultraestrutura , Reatores Biológicos/microbiologia , Biotecnologia/métodos , Fatores de TempoRESUMO
The diversity of myxobacteria present in campus garden soil was surveyed by both cultivation-based and cultivation-independent methods. Detailed phylogenetic analysis of cultured and uncultured myxobacteria 16S rRNA gene sequences revealed that many undescribed relatives of the myxobacteria exist in nature. Molecular systematic analyses also revealed that myxobacterial genera described to date on the basis of the morphology of multi-cellular fruiting bodies were mostly monophyletic. However, these known taxa comprised only in a small part of the sequences recovered directly from soil in a cultivation-independent approach, indicating that the group is much more diverse than previously thought. We propose that the myxobacteria exist in two forms: the fruiting and the non-fruiting types. Most of the uncultured myxobacteria may represent taxa which rarely form fruiting bodies, or may lack some or all of the developmental genes needed for fruiting body formation. In order to identify non-fruiting myxobacteria, new morphology-independent cultivation and isolation techniques need to be developed.
Assuntos
Myxococcales/classificação , Myxococcales/genética , Filogenia , Sequência de Bases , Genes Bacterianos/genética , Viabilidade Microbiana , Myxococcales/citologia , RNA Ribossômico 16S/genéticaRESUMO
Tubulysin A (tubA) is a natural product isolated from a strain of myxobacteria that has been shown to depolymerize microtubules and induce mitotic arrest. The potential of tubA as an anticancer and antiangiogenic agent is explored in the present study. tubA shows potent antiproliferative activity in a panel of human cancer cell lines irrespective of their multidrug resistance properties. It induces apoptosis in cancer cells but not in normal cells and shows significant potential antiangiogenic properties in several in vitro assays. It is efficacious in initial animal studies using a hollow fibre assay with 12 different human tumour cell lines. This study suggests that both in vitro and preclinical profiles of tubA may translate into clinically useful anticancer properties.
Assuntos
Inibidores da Angiogênese/uso terapêutico , Antineoplásicos/uso terapêutico , Avaliação Pré-Clínica de Medicamentos , Oligopeptídeos/farmacologia , Moduladores de Tubulina/farmacologia , Membro 1 da Subfamília B de Cassetes de Ligação de ATP/metabolismo , Inibidores da Angiogênese/metabolismo , Inibidores da Angiogênese/farmacologia , Antineoplásicos/farmacologia , Apoptose/efeitos dos fármacos , Produtos Biológicos/metabolismo , Produtos Biológicos/farmacologia , Neoplasias da Mama/tratamento farmacológico , Neoplasias da Mama/metabolismo , Linhagem Celular Tumoral , Proliferação de Células/efeitos dos fármacos , Células Cultivadas , Neoplasias Colorretais/tratamento farmacológico , Neoplasias Colorretais/metabolismo , Sistema Enzimático do Citocromo P-450/metabolismo , Resistência a Múltiplos Medicamentos , Células Endoteliais/metabolismo , Feminino , Células HCT116 , Humanos , Myxococcales/citologia , Myxococcales/metabolismo , Oligopeptídeos/metabolismo , Especificidade por Substrato , Moduladores de Tubulina/metabolismoRESUMO
A new experimental colonial pattern and pattern transition observed in E. coli MG1655 swarming cells grown on semisolid agar are described. We present a reaction-diffusion model that, taking into account the slime generated by these cells and its influence on the bacterial differentiation and motion, reproduces the pattern and successfully predicts the observed changes when the colonial collective motility is limited. In spite of having small nonhyperflagellated swarming cells, under these experimental conditions E. coli MG1655 can very rapidly colonize a surface, with a low branching rate, thanks to a strong fluid production and a locally incremented density of motile, lubricating cells.
Assuntos
Biofilmes/crescimento & desenvolvimento , Escherichia coli/citologia , Escherichia coli/fisiologia , Modelos Biológicos , Myxococcales/citologia , Myxococcales/fisiologia , Aderência Bacteriana/fisiologia , Biomassa , Proliferação de Células , Contagem de Colônia Microbiana/métodos , Simulação por Computador , Difusão , Reconhecimento Automatizado de Padrão/métodosRESUMO
Myxococcus xanthus is a common Gram-negative bacterium that moves by a process called gliding motility. In myxobacteria, two distinct mechanisms for gliding have been discovered. S-type motility requires the extension, attachment, and retraction of type IV pili. The other mechanism, designated as A-type motility, may be driven by the secretion and swelling of slime; however, experiments to confirm or refute this model are still lacking and the force exerted by this mechanism has not been measured. A previously published experiment found that when an M. xanthus cell became stuck at one end, the cell underwent flailing motions. Based on this experiment, I propose an elastic model that can estimate the force produced by the A-motility engine and the bending modulus of a single myxobacterial cell. The model estimates a bending modulus of 3 x 10(-14) erg cm and a force between 50-150 pN. This force is comparable to that predicted by slime extrusion, and the bending modulus is 30-fold smaller than that measured in Bacillus subtilis. This model suggests experiments that can further quantify this process.
Assuntos
Fímbrias Bacterianas/fisiologia , Modelos Biológicos , Proteínas Motores Moleculares/fisiologia , Myxococcales/fisiologia , Adesão Celular/fisiologia , Simulação por Computador , Elasticidade , Fímbrias Bacterianas/ultraestrutura , Movimento (Física) , Myxococcales/citologia , Estresse MecânicoRESUMO
The long, rod-shaped cells of myxobacteria are polarized by their gliding engines. At the rear, A-engines push while pili pull the front end forward. An hypothesis is developed whereby both engines are partially dis-assembled, then re-assembled at the opposite pole when cells reverse their movement direction. Reversals are induced by an Mgl G-protein switch that controls engine polarity. The switch is driven by an oscillatory circuit of Frizzy proteins. In growing cells, the circuit gives rise to an occasional reversal that makes swarming possible. Then, as myxobacteria begin fruiting body development, a rising level of C-signal input drives the oscillator and changes the reversal pattern. Cells reverse regularly every eight minutes in traveling waves, the reversal period is then prolonged enabling cells to form streams that enlarge tiny random aggregates into fruiting bodies.