Association of flexing and gliding in Flexibacter.
Nongliding mutants of Flexibacter FS-1 are unable to flex; revertants regain both forms of movement. A variety of conditions and treatments reversibly inhibit both gliding and flexing.
Cyanides↗
Biomedical subjects
R P Burchard
Publications and source records attributed to R P Burchard.
Effect of cell length on gliding motility of Flexibacter.
Short Flexibacter FS-1 cells, generated during logarithmic growth in glucose-salts medium or by filament fragmentation during the transition from log to stationary phase in rich medium, are unable to glide. Motility returns when cells elongate. This strain also dissociates stable, short, nongliding variants.
Cytophagaceae↗
Intracellular, periodic structures in the gliding bacterium Myxococcus xanthus.
Electron microscopic observations of thin sections of Myxococcus xanthus vegetative cells revealed the presence of cytoplasmic bundles of 4- to 5-nm-diameter filaments running longtitudinally below the cell membrane and terminating in association with the envelope near one pole. Part of each bundle demonstrated a herringbone-like periodicity (approximately 12-nm spacing). This structure was observed in cells from shake cultures and in gliding cells fixed by several methods. It is proposed that the structure may be attached to the envelope near both poles in gliding cells and that the motive force for motility may be provided by its contraction and relaxation. In one of four nongliding mutants examined, the periodicity was indistinct or lacking. In this mutant another structure, comprised of linearly arrayed beads, was observed in association with the filamentous bundle. Another structure, characterized by major, transverse bands (approximately 34 nm apart), occurred in patches that may traverse the diameter of the wild-type cells in which the structure was observed.
Cell Wall↗
Pigmentation phenotype instability in Myxococcus xanthus.
Cells of Myxococcus xanthus FB2 produce tan or yellow colonies. Subcultures of tan colonies yielded tan and yellow colonies and subcultures of most yellow colonies yielded only yellow colonies. Strain FB2 variants in which the color type is more stable were obtained. Yellow cells were distinguishable from tan by the presence of pigment(s) with an absorption maximum at 379 nm. Fluctuation Test experiments and the presence of this pigment(s) in liquid cultures of FB2 indicated that tan phenotype cells spontaneously became or segregated yellow cells in liquid culture. The frequency of appearance of yellow cells was increased in low density cultures (less than 10(6)/ml). The increase cannot be explained by differences in growth rates of the two phenotypes. No evidence that cell-cell contact or culture medium constituents affect the appearance of the yellow phenotype was found. Ultraviolet irradiation of FB2 resulted in an increased proportion of cells producing yellow colonies among the survivors. Greater UV resistance of yellow cells and UV-induced conversion of tan to yellow accounts for this increase. Low level photoreactivation of viability and of the tan phenotype occurred. Incubation of FB2 in medium containing mitomycin C, nalidixic acid, phenethyl alcohol, or at 36.5 degrees C also resulted in conversion of tan to yellow cells.
Myxococcales↗
Phage and defective phage of strains of Myxococcus.
1. Phage-like particles were found in the supernatants of cultures of strains of Myxococcus xanthus, M. virescens and M. fulvus. The largest number of such particles was associated with M. virescens V2. Most of the particles were similar in morphology to the virulent Myxococcus phage, MX-1. 2. Several new phages were isolated from soil and animal droppings. A new phage was isolated from cultures of M. virescens V2. All resembled phage MX-1 in morphology and were related to phage MX-1 serologically. One of these phage, om, was characterized by fractionation of its proteins by SDS-polyacrylamide gel electrophoresis and by analysis of restriction fragments of its DNA. The very close relatedness with MX-1 was confirmed by these techniques. Phage om, was found to exist in a state of pseudolysogeny with strains of M. virescens and M. fulvus. 3. Two types of bacteriocin-like activity were found associated with Myxococcus strains. In one case, the activity was extracted from chloroformkilled or from sonicated cells. In the second case it was associated with extracellular material. Strains of Salmonella and Cytophaga were found to be good indicators for this latter activity. These strains were found to be killed by phage MX-1. 4. The significance of these data for origin of the phages of myxococci are discussed and it is proposed that MX-1 and the newly isolated phages may be virulent mutants of a family of lysogenic phages.
Bacteriocins↗
Mutants of Myxococcus xanthus insensitive to glycerol-induced myxospore formation.
Mutants of Myxococcus xanthus FBt unable to form myxospores in response to 0.5 M glycerol arise spontaneously with a frequency of 1--3 X 10(-5). These mutants are designated glc. Ultraviolet mutagenesis increases the frequency to a maximum of 7% of the survivors. The reversion frequency following ultraviolet irradiation of spontaneous glc mutants is less than 10(-3). Of four glc mutants examined, none form myxospores in response to the alternative inducers, ethylene glycol and dimethyl sulphoxide. One glc mutant is induced by 1.5 M glycerol; strain FBt responds to this glycerol concentration with low efficiency myxospore formation. Strain FBt and glc mutants all produce myxospores with low efficiency in response to phenyl ethanol. Of 117 glc mutants tested, 109 form fruiting bodies containing mature myxospores; thus, mutations to the glc phenotype do not normally block myxospore formation within the fruiting cycle of the organism.
Dimethyl Sulfoxide↗
Chloramphenicol resistance in Myxococcus xanthus.
Derivatives of Myxococcus xanthus FB(t) resistant to chloramphenicol (25 mug/ml) arose spontaneously with a frequency of approximately 10(-7). One of these organisms (FB(t)Cam(1) (r)) was characterized. FB(t)Cam(1) (r) showed a unique type of phenotypic instability. After transfer from medium containing chloramphenicol to medium lacking the drug, resistance was lost after approximately one generation. The loss resulted in a sharp drop in the total number of chloramphenicol-resistant organisms and was not due to segregation of chloramphenicol-susceptible organisms during growth. Cell-free extracts of strain FB(t)Cam(1) (r) converted chloramphenicol to acetyl chloramphenicols in a fashion implicating activity of chloramphenicol acetyltransferase. This activity was lost simultaneously with the loss of chloramphenicol resistance after removal of the drug from cultures. Organisms with a similar phenotype to FB(t)Cam(1) (r) could be produced at high frequencies when strain FB(t) was exposed to low concentrations of chloramphenicol (2 to 5 mug/ml), to 3-acetylchloramphenicol (25 mug/ml), or to 1,3-diacetylchloramphenicol (25 mug/ml). Since strain FB(t) is capable of deacetylating acetyl chloramphenicols, these effects are probably all due to low concentrations of chloramphenicol. In the presence of chloramphenicol, FB(t)Cam(1) (r) produced fruiting bodies and myxospores on fruiting agar; however, glycerol-induced myxospore formation was inhibited. In the absence of the antibiotic, chloramphenicol resistance was maintained by glycerol-induced myxospores.
Chloramphenicol↗
Myxospore induction in a nondispersed growing mutant of Myxococcus xanthus.
Myxococcus xanthus RB5, a rough-colony-forming, nondispersed growing mutant of strain FBt, forms macroscopic, multicellular masses of radially oriented cells in shake cultures. The cells appear to be held together by slime fibrils. Physical and enzymatic methods to disrupt the spheres were unsuccessful as were attempts to isolate dispersed growing mutants. During incubation of the spheres in starvation medium, the cells within convert to myxospores, indistinguishable from those formed in fruiting bodies. Myxospores were also induced in artifically constructed, dense masses of cells of a nonmotile strain.
Agar↗
Nitrogen fixation in the Rhode River estuary of Chesapeake Bay.
The distribution, seasonal variation, origin, and significance of biological nitrogen fixation has been determined for a Chesapeake Bay estuary using the acetylene reduction technique. Studies over a 15-month period have shown that nitrogen fixation occurs predominantly in the surface intertidal (marsh) and subtidal sediments. Negligible activity was found in surface waters. A marked seasonal variation in nitrogen fixation was observed for intertidal sediments incubated at a standard 20 degrees C. Average rates of about 37 and 12 ng N/g dry sediment per hour were observed in the late fall months of 1972 and 1973, respectively, and less than or equal to 5 ng N/g dry sediment per hour during other seaons. Peaks of activity were lowered considerably when samples were incubated at ambient temperatures (in situ). Activity in the subtidal sediments was low (less than or equal to 6.8 ng N/g dry sediment per hour but showed a similar (approximately twofold) seasonal variation in nitrogen fixation potential. Light-dark and substrate addition experiments suggest that heterotrophic bacteria are the principal agents for nitrogen fixation in sediments. Integrated estimates of nitrogen fixation in the estuary indicate that biological fixation probably accounts for less than 5% of the total influx of nitrogen into the system. Rates of activity in the intertidal sediments are insufficient to account for the high productivity of marine angiosperms found in the marsh.
Acetylene↗