A structural framework for a near-minimal form of life: mass and compositional analysis of the helical mollicute Spiroplasma melliferum BC3.

Spiroplasma melliferum is a wall-less bacterium with dynamic helical geometry. This organism is geometrically well defined and internally well ordered, and has an exceedingly small genome. Individual cells are chemotactic, polar, and swim actively.

Unperturbing a non-helically perturbed bacterial flagellar filament: Salmonella typhimurium SJW23.

Salmonella typhimurium SJW23 has a right-handed, non-helically perturbed filament of serotype gt with a unique surface pattern. Non-helical perturbations involve symmetry reduction along the five-start helical lines resulting in layer lines of fractional Bessel orders and a consequent seam. The flagellin gene, fliC(23), which we sequenced, differs from the sequence of the canonic, plain SJW1655 flagellin, fliC(1655).

The monomeric, tetrameric, and fibrillar organization of Fib: the dynamic building block of the bacterial linear motor of Spiroplasma melliferum BC3.

Spiroplasmas belong to the class Mollicutes, representing the minimal, free-living, and self-replicating forms of life. Spiroplasmas are helical wall-less bacteria and the only ones known to swim by means of a linear motor (rather than the near-universal rotary bacterial motor). The linear motor follows the shortest path along the cell's helical membranal tube.

Structure of the cytoskeleton of Spiroplasma melliferum BC3 and its interactions with the cell membrane.

Spiroplasma melliferum is a wall-less bacterium with dynamic helical symmetry. Taking advantage of the simplicity of this primitive lifeform, we have used structural (electron tomography and freeze fracture of whole cells; cryoelectron tomography and diffraction analysis of isolated cytoskeletons) and proteomic approaches to elucidate the basic organizing principles of its minimal yet functional cytoskeleton. From among approximately 30 Spiroplasma proteins present in a highly purified cytoskeletal fraction, we identify three major putative structural proteins: Fib, MreB, and elongation factor Tu.

The flagellar filament structure of the extreme acidothermophile Sulfolobus shibatae B12 suggests that archaeabacterial flagella have a unique and common symmetry and design.

Archaea, constituting a third domain of life between Eubacteria and Eukarya, characteristically inhabit extreme environments. They swim by rotating flagellar filaments that are phenomenologically and functionally similar to those of eubacteria. However, biochemical, genetic and structural evidence has pointed to significant differences but even greater similarity to eubacterial type IV pili.

The cytoskeleton of spiroplasma: a complex linear motor.

Spiroplasma are wall-less, helical bacteria from the class Mollicutes. The Mollicutes (Mycoplasma, Acholeplasma, Spiroplasma) evolved by regressive evolution to generate one of the simplest and minimal free-living and self-replicating forms of life. The spiroplasmas are the more advanced members in the class and are the closest to their clostridial ancestors.

The archaeabacterial flagellar filament: a bacterial propeller with a pilus-like structure.

Common prokaryotic motility modes are swimming by means of rotating internal or external flagellar filaments or gliding by means of retracting pili. The archaeabacterial flagellar filament differs significantly from the eubacterial flagellum: (1) Its diameter is 10-14 nm, compared to 18-24 nm for eubacterial flagellar filaments. (2) It has 3.

Refining the structure of the Halobacterium salinarum flagellar filament using the iterative helical real space reconstruction method: insights into polymorphism.

The eubacterial flagellar filament is an external, self-assembling, helical polymer approximately 220 A in diameter constructed from a highly conserved monomer, flagellin, which polymerizes externally at the distal end. The archaeal filament is only approximately 100 A in diameter, assembles at the proximal end and is constructed from different, glycosylated flagellins. Although the phenomenology of swimming is similar to that of eubacteria, the symmetry of the archebacterial filament is entirely different.

Shaping and moving a spiroplasma.

The Mollicutes (Spiroplasma, Mycoplasma and Acholeplasma) are the most minimal cells known to exist, being the smallest and simplest free-living and self-replicating forms of life. Phylogenetically, the Mollicutes are related to gram-positive bacteria and have evolved, by regressive evolution and genome reduction, from Clostridia. The smallest genome in this group (Mycoplasma genitalium - 5.

Bacterial flagellar microhydrodynamics: Laminar flow over complex flagellar filaments, analog archimedean screws and cylinders, and its perturbations.

The flagellar filament, the bacterial organelle of motility, is the smallest rotary propeller known. It consists of 1), a basal body (part of which is the proton driven rotary motor), 2), a hook (universal joint-allowing for off-axial transmission of rotary motion), and 3), a filament (propeller-a long, rigid, supercoiled helical assembly allowing for the conversion of rotary motion into linear thrust). Helically perturbed (so-called "complex") filaments have a coarse surface composed of deep grooves and ridges following the three-start helical lines.

The axial alpha-helices and radial spokes in the core of the cryo-negatively stained complex flagellar filament of Pseudomonas rhodos: recovering high-resolution details from a flexible helical assembly.

Of the two known "complex" flagellar filaments, those of Pseudomonas are far more flexible than those of Rhizobium. Their diameter is larger and their outer three-start ridges and grooves are more prominent. Although the symmetry of both complex filaments is similar, the polymer's linear mass density and the flagellin molecular mass of the latter are lower.

The structure of the helically perturbed flagellar filament of Pseudomonas rhodos: implications for the absence of the outer domain in other complex flagellins and for the flexibility of the radial spokes.

Bacterial flagella, the organelles of motility, are commonly divided into two classes: 'plain' and 'complex'. The complex filaments are pairwise, helically perturbed forms of the plain filaments and have been reported to occur only in Rhizobium and Pseudomonas. Previously, we reconstructed and analysed the structure of the complex filaments of Rhizobium lupini H13-3 and determined their unique symmetry and origin of the perturbations (Trachtenberg et al.

Mass distribution and spatial organization of the linear bacterial motor of Spiroplasma citri R8A2.

In the simple, helical, wall-less bacterial genus Spiroplasma, chemotaxis and motility are effected by a linear, contractile motor arranged as a flat cytoskeletal ribbon attached to the inner side of the membrane along the shortest helical line. With scanning transmission electron microscopy and diffraction analysis, we determined the hierarchical and spatial organization of the cytoskeleton of Spiroplasma citri R8A2. The structural unit appears to be a fibril, approximately 5 nm wide, composed of dimers of a 59-kDa protein; each ribbon is assembled from seven fibril pairs.

The bacterial linear motor of Spiroplasma melliferum BC3: from single molecules to swimming cells.

Spiroplasma melliferum BC3 are wall-less bacteria with internal cytoskeletons. Spiroplasma, Mycoplasma and Acholeplasma belong to the Mollicutes, which represent the smallest, simplest and minimal free-living and self-replicating forms of life. The Mollicutes are motile and chemotactic.

Motility modes of Spiroplasma melliferum BC3: a helical, wall-less bacterium driven by a linear motor.

Spiroplasma are members of the Mollicutes (Mycoplasma, Acholeplasma and Spiroplasma) - the simplest, minimal, free-living and self-replicating forms of life. The mollicutes are unique among bacteria in completely lacking cell walls and flagella and in having an internal, contractile cytoskeleton, which also functions as a linear motor. Spiroplasma are helical, chemotactic and viscotactic active swimmers.

The structure of the archeabacterial flagellar filament of the extreme halophile Halobacterium salinarum R1M1 and its relation to eubacterial flagellar filaments and type IV pili.

Although the phenomenology and mechanics of swimming are very similar in eubacteria and archaeabacteria (e.g. reversible rotation, helical polymorphism of the filament and formation of bundles), the dynamic flagellar filaments seem completely unrelated in terms of morphogenesis, structure and amino acid composition.