Morphology and dynamics of protruding spirochete periplasmic flagella.

We recently characterized the three-dimensional shape of Treponema phagedenis periplasmic flagella (PFs). In the course of these studies, we observed protrusions on swimming cells that resembled PFs. Here we present a detailed characterization of the shape, structure, and motion of these protrusions. Although protrusion formation occurred primarily in wild-type cells during the stationary phase, a large fraction of exponential-phase cells of cell cylinder helicity mutants (greater than 90% of mutant T-52) had protrusions. These results suggest that cells bearing protrusions can still participate in cell division. T. phagedenis protrusions had the identical helix handedness, pitch, and diameter to those of purified PFs. Protrusions were not present on mutants unable to synthesize PFs, but were present in all motile revertants which regained PFs. These results, taken together with electron microscope observations, suggest that protrusions consist of PFs surrounded by an outer membrane sheath. To analyze protrusion movements, we held cells against a coverglass surface with optical tweezers and observed the motion of protrusions by video-enhanced differential interference contrast light microscopy. Protrusions were found to gyrate in both clockwise and counterclockwise directions, and direct evidence was obtained that protrusions rotate. Protrusions were also observed on Treponema denticola and Borrelia burgdorferi. These were also left-handed and had the same helix handedness, pitch, and diameter as purified PFs from their respective species. The PFs from T. denticola had a helix diameter of 0.26 microns and a helix pitch of 0.78 micron; PFs from B. burgdorferi had a helix diameter of 0.28 micron and a helix pitch of 1.48 microns. Protrusions from these spirochete species had similar structures and motion to those of T. phagedenis. Our results present direct evidence that PFs rotate and support previously proposed models of spirochete motility.     

Genetic analysis of spirochete flagellin proteins and their involvement in motility, filament assembly, and flagellar morphology

The filaments of spirochete periplasmic flagella (PFs) have a unique structure and protein composition. In most spirochetes, the PFs consist of a core of at least three related proteins (FlaB1, FlaB2, and FlaB3) and a sheath of FlaA protein. The functions of these filament proteins remain unknown. In this study, we used a multidisciplinary approach to examine the role of these proteins in determining the composition, shape, and stiffness of the PFs and how these proteins impact motility by using the spirochete Brachyspira (formerly Treponema, Serpulina) hyodysenteriae as a genetic model. A series of double mutants lacking combinations of these PF proteins was constructed and analyzed. The results show the following. First, the diameters of PFs are primarily determined by the sheath protein FlaA, and that FlaA can form a sheath in the absence of an intact PF core. Although the sheath is important to the PF structure and motility, it is not essential. Second, the three core proteins play unequal roles in determining PF structure and swimming speed. The functions of the core proteins FlaB1 and FlaB2 overlap such that either one of these proteins is essential for the spirochete to maintain the intact PF structure and for cell motility. Finally, linear elasticity theory indicates that flagellar stiffness directly affects the spirochete's swimming speed.     

Spiral cell wall growth in zygnemataceae

Using two species ofSpirogyra and one species ofZygnema, it was demonstrated on a quantitative basis that these algal filaments grow while twisting around their own axis. The sense of spiral growth of the cell wall inSpirogyra-1 was always left-handed being coincident with the sense of chloroplast helix. InSpirogyra-2, the growth vector of the cell wall was likewise left-handed in most cases, but there occurred right-handed growth also. InZygnema both left-handed and right-handed senses of spiral growth were found in nearly equal frequencies. Besides the natural cell wall growth, the effects of longitudinal tension and turgor pressure on elongation and twisting of the filaments were briefly studied. It was shown that the cell wall of Zygnemataceae exhibited mechanical anisotropy in helical direction.     

Structural and Biochemical Analysis of the Sheath of Phormidium uncinatum

The sheath of the filamentous, gliding cyanobacterium Phormidium uncinatum was studied by using light and electron microscopy. In thin sections and freeze fractures the sheath was found to be composed of helically arranged carbohydrate fibrils, 4 to 7 nm in diameter, which showed a substantial degree of crystallinity. As in all other examined motile cyanobacteria, the arrangement of the sheath fibrils correlates with the motion of the filaments during gliding motility; i.e., the fibrils formed a right-handed helix in clockwise-rotating species and a left-handed helix in counterclockwise-rotating species and were radially arranged in nonrotating cyanobacteria. Since sheaths could only be found in old immotile cultures, the arrangement seems to depend on the process of formation and attachment of sheath fibrils to the cell surface rather than on shear forces created by the locomotion of the filaments. As the sheath in P. uncinatum directly contacts the cell surface via the previously identified surface fibril forming glycoprotein oscillin (E. Hoiczyk and W. Baumeister, Mol. Microbiol. 26:699–708, 1997), it seems reasonable that similar surface glycoproteins act as platforms for the assembly and attachment of the sheaths in cyanobacteria. In P. uncinatum the sheath makes up approximately 21% of the total dry weight of old cultures and consists only of neutral sugars. Staining reactions and X-ray diffraction analysis suggested that the fibrillar component is a homoglucan that is very similar but not identical to cellulose which is cross-linked by the other detected monosaccharides. Both the chemical composition and the rigid highly ordered structure clearly distinguish the sheaths from the slime secreted by the filaments during gliding motility.     

The spirochete FlaA periplasmic flagellar sheath protein impacts flagellar helicity

Spirochete periplasmic flagella (PFs), including those from Brachyspira (Serpulina), Spirochaeta, Treponema, and Leptospira spp., have a unique structure. In most spirochete species, the periplasmic flagellar filaments consist of a core of at least three proteins (FlaB1, FlaB2, and FlaB3) and a sheath protein (FlaA). Each of these proteins is encoded by a separate gene. Using Brachyspira hyodysenteriae as a model system for analyzing PF function by allelic exchange mutagenesis, we analyzed purified PFs from previously constructed flaA::cat, flaA::kan, and flaB1::kan mutants and newly constructed flaB2::cat and flaB3::cat mutants. We investigated whether any of these mutants had a loss of motility and altered PF structure. As formerly found with flaA::cat, flaA::kan, and flaB1::kan mutants, flaB2::cat and flaB3::cat mutants were still motile, but all were less motile than the wild-type strain, using a swarm-plate assay. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis indicated that each mutation resulted in the specific loss of the cognate gene product in the assembled purified PFs. Consistent with these results, Northern blot analysis indicated that each flagellar filament gene was monocistronic. In contrast to previous results that analyzed PFs attached to disrupted cells, purified PFs from a flaA::cat mutant were significantly thinner (19.6 nm) than those of the wild-type strain and flaB1::kan, flaB2::cat, and flaB3::cat mutants (24 to 25 nm). These results provide supportive genetic evidence that FlaA forms a sheath around the FlaB core. Using high-magnification dark-field microscopy, we also found that flaA::cat and flaA::kan mutants produced PFs with a smaller helix pitch and helix diameter compared to the wild-type strain and flaB mutants. These results indicate that the interaction of FlaA with the FlaB core impacts periplasmic flagellar helical morphology.     

Treponema phagedenis has at least two proteins residing together on its periplasmic flagella.

Treponema phagedenis is an anaerobic, motile spirochete with several periplasmic flagella (PFs) at each cell end. This study provides the first genetic evidence that multiple protein species are associated with the PFs. In addition, these proteins were found to reside together on a given PF. Nonmotile mutants which lacked the PFs were isolated, and spontaneous revertants to motility regained the PFs. These results suggest that the PFs are involved in the motility of T. phagedenis. Isolated PFs had two major protein bands with molecular weights of 33,000 and 39,800, as revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Western blots with monoclonal and polyclonal antibodies indicated that both proteins were absent in the PF mutants but present in the revertants. Immunoelectron microscopy revealed that the 39,800-molecular-weight protein was distributed along the entire PF. Immunoprecipitation analysis suggested that the 39,800- and 33,000-molecular-weight proteins were closely associated in situ.     

Microcinematographic analysis of tethered Leptospira illini.

A model of Leptospira motility was recently proposed. One element of the model states that in translating cells the anterior spiral-shaped end gyrates counterclockwise and the posterior hook-shaped end gyrates clockwise. We tested these predictions by analyzing cells tethered to a glass surface. Leptospira illini was incubated with antibody-coated latex beads (Ab-beads). These beads adhered to the cells, and subsequently some cells became attached to either the slide or the cover glass via the Ab-beads. As previously reported, these cells rapidly moved back and forth across the surface of the beads. In addition, a general trend was observed: cells tethered to the cover glass rotated clockwise around the Ab-bead; cells tethered to the slide rotated counterclockwise around the Ab-bead. A computer-aided microcinematographic analysis of tethered cells indicated that the direction of rotation of cells around the Ab-bead was a function of both the surface of attachment and the shape of the cell ends. The results can best be explained by assuming that the gyrating ends interact with the glass surface to cause rotation around the Ab-beads. The analysis obtained indicates that the hook- and spiral-shaped ends rotate in the directions predicted by the model. In addition, the tethered cell assay permitted detection of rapid, coordinated reversals of the cell ends, e.g., cells rapidly switched from a hook-spiral configuration to a spiral-hook configuration. These results suggest the existance of a mechanism which coordinates the shape of the cell ends of L. illini.     

Three Mutations in Escherichia coli That Generate Transformable Functional Flagella

Hydrodynamics predicts that swimming bacteria generate a propulsion force when a helical flagellum rotates because rotating helices necessarily translate at a low Reynolds number. It is generally believed that the flagella of motile bacteria are semirigid helices with a fixed pitch determined by hydrodynamic principles. Here, we report the characterization of three mutations in laboratory strains of Escherichia coli that produce different steady-state flagella without losing cell motility. E. coli flagella rotate counterclockwise during forward swimming, and the normal form of the flagella is a left-handed helix. A single amino acid exchange A45G and a double mutation of A48S and S110A change the resting flagella to right-handed helices. The stationary flagella of the triple mutant were often straight or slightly curved at neutral pH. Deprotonation facilitates the helix formation of it. The helical and curved flagella can be transformed to the normal form by torsion upon rotation and thus propel the cell. These mutations arose in the long-term laboratory cultivation. However, flagella are under strong selection pressure as extracellular appendages, and similar transformable flagella would be common in natural environments.     

GLIDING MOTILITY IN THE BLUE-GREEN ALGA OSCILLATORIA PRINCEPS1

Gliding is an active movement displayed by a microorganism in contact with a solid substrate where there is no evidence of a motility organelle or of a conformational change in the organism. Gliding may be accompanied by rotations, reversals, flectional activity, and mucilage sheath production, as well as linear translation. Previous explanations of the mechanism responsible did not consider all these aspects of behavior. The gliding behavior and ultrastructure of the blue-green alga Oscillatoria princeps Vaucher were examined. O. princeps has a maximum observed gliding rate of 11.1 μm/sec. The trichomes can glide in either longitudinal direction following rapid and occasionally frequent reversals. Right-handed trichome rotation was always observed, which means that any surface point on these trichomes traces a 60-deg right-handed helix. A mucilage sheath envelopes the moving trichomes. The rate of gliding was reduced by viscous substrates, extreme pH, lysozyme, DNP, and cyanide, while sustained darkness had no inhibitory effect. Ultrastructurally, the cell wall is composed of an L-1 layer which is 10 nm thick and often ill-defined. The L-2 layer which is outside this is 200 nm thick and participates in septum formation. The L-3 layer is outside the L-2 and is continuous over the trichome surface. The L-4 “membrane” lies outside the L-3 layer. Grazing surface sections and freeze-etch replicas show a parallel and tight array of 6–9 nm wide continuous fibrils in the cell wall on the surface of the distinctive L-2 layer. Isolated wall fragments were tightly coiled inside out with the fibrils on the inside. The angle of orientation for the fibrils was to the right in a helix with a pitch of 60 deg. O. animalis, a blue-green alga with a movement tracing a left-handed helix, showed a similar array of fibrils oriented in a left-handed helix with a pitch of 60 deg. It is proposed that gliding is produced by unidirectional waves of bending in the fibrils which, act against the sheath or substrate, tints displacing the trichome.     

The flagellar cytoskeleton of the spirochetes

The recent discoveries of prokaryotic homologs of all three major eukaryotic cytoskeletal proteins (actin, tubulin, intermediate filaments) have spurred a resurgence of activity in the field of bacterial morphology. In spirochetes, however, it has long been known that the flagellar filaments act as a cytoskeletal protein structure, contributing to their shape and conferring motility on this unique phylum of bacteria. Therefore, revisiting the spirochete cytoskeleton may lead to new paradigms for exploring general features of prokaryotic morphology. This review discusses the role that the periplasmic flagella in spirochetes play in maintaining shape and producing motility. We focus on four species of spirochetes: Borrelia burgdorferi, Treponema denticola, Treponema phagedenis and Leptonema (formerly Leptospira) illini. In spirochetes, the flagella reside in the periplasmic space. Rotation of the flagella in the above species by a flagellar motor induces changes in the cell morphology that drives motility. Mutants that do not produce flagella have a markedly different shape than wild-type cells.     

2H nuclear magnetic resonance of the gramicidin A backbone in a phospholipid bilayer.

Solid-state 2H NMR spectroscopy has been employed to study the channel conformation of gramicidin A (GA) in unoriented 1,2-dimyristoyl-sn-glycerol-3-phosphocholine (DMPC) multilayers. Quadrupolar echo spectra were obtained at 44 degrees C and 53 degrees C, from gramicidin A labels in which the proton attached to the alpha carbon of residue 3, 4, 5, 10, 12, or 14 was replaced with deuterium. Because of the nearly axially symmetric electric field gradient tensor, the quadrupolar splittings obtained from an unoriented multilamellar dispersion of DMPC and singly labeled GA directly yield unambiguous orientational constraints on the C-2H bonds. The average of the ratios of the quadrupolar splittings of the left-handed amino acids to those of the right-handed amino acids, (delta vQL/delta vQD), is expected to be 0.97 +/- 0.04 for a relaxed right-handed beta 6.3LD helix, while a ratio of 0.904 +/- 0.003 is expected for a left-handed beta LD6.3 helix. Since we have experimentally determined this ratio to be 1.01 +/- 0.04, we conclude that that the helix sense of the channel conformation of GA is right-handed. Assuming that the dominant motions are fast axial diffusion of the gramicidin molecule and reorientation of the diffusion axis with respect to the local bilayer normal, then the theoretical splittings may all be scaled down by a constant motional narrowing factor. In this case, a relaxed right-handed beta LD6.3 helix, whose axis of motional averaging is roughly along the presumed helix axis, gave the best fit to experimental results. The reasonably uniform correspondence between the splittings predicted by the relaxed right-handed beta LD6.3 helix and the observed splittings, for labels from both the inner and outer turn of GA, did not reflect a peptide backbone flexibility gradient, since an outer turn (i.e., the turn of the helix closest to the interface with water) with greater flexibility would show additional motional narrowing for labels located there.     

Proposal of a new hydrogen-bonding form to maintain curdlan triple helix

Curdlan and other beta-1,3-D-glucans form right-handed triple helices, and it has been believed that the intermolecular H-bond is present at the center of the helix to maintain the structure. In this H-bond model, three secondary OH groups form an inequilateral hexagonal shape perpendicular to the helix axis. This hexagonal form seems to be characteristic for beta-1,3-D-glucans and is widely accepted. We carried out MOPAC and ab initio calculations for the curdlan helix, and we propose a new intermolecular H-bonding model. In our model, the H-bonds are formed between the O2-atoms on different x-y planes along the curdlan helix, hence the H-bonds are not perpendicular to the helix axis. The new H-bonds are connected along the helix, traversing three curdlan chains to make a left-handed helix. Therefore, the H-bonding array leads to a reverse helix of the main chain. According to our MOPAC calculation, this model is more stable than the previous one. We believe that the continuous H-bonding array is stabilized by cooperative phenomena in the polymeric system.     

Determination of the absolute hand of the helix in the nucleocapsid of haemagglutinating virus (Japan)

The basic hand of the helix of the nucleocapsid of haemagglutinating virus (Japan) was determined to be left-handed from observation of serrated-smooth asymmetry in tilted specimens examined in the electron microscope according to Finch's (1972) technique. Absolute determination of the helical hand was made by comparison with a tilted model of the virus nucleocapsid and by comparing this with the helical sense of the tobacco mosaic virus particle determined by the same method.The left-handed sense of the helix in the nucleocapsid was recognized by examination of cases showing opened-out turns of the helices. Under these conditions the far side of the particle was found to be contrasted predominantly. These conditions are discussed.     

Formation of hyaluronan- and versican-rich pericellular matrix by prostate cancer cells promotes cell motility

Previous studies have demonstrated that high levels of hyaluronan (HA) and the chondroitin sulfate proteoglycan, versican in the peritumoral stroma are associated with metastatic spread of clinical prostate cancer. In vitro integration of HA and versican into a pericellular sheath is a prerequisite for proliferation and migration of vascular smooth muscle cells. In this study, a particle exclusion assay was used to determine whether human prostate cancer cell lines are capable of assembling a pericellular sheath following treatment with versican-containing medium and whether formation of a pericellular sheath modulated cell motility. PC3 and DU145, but not LNCaP cells formed prominent polarized pericellular sheaths following treatment with prostate fibroblast-conditioned medium. The capacity to assemble a pericellular sheath correlated with the ability to express membranous HA receptor, CD44. HA and versican histochemical staining were observed surrounding PC3 and DU145 cells following treatment with prostatic fibroblast-conditioned medium. The dependence on HA for integrity of the pericellular sheath was demonstrated by its removal following treatment with hyaluronidase. Purified versican or conditioned medium from Chinese hamster ovary K1 cells overexpressing versican V1, but not conditioned medium from parental cells, promoted pericellular sheath formation and motility of PC3 cells. Using time lapse microscopy, motile PC3 cells treated with versican but not non-motile cells exhibited a polar pericellular sheath. Polar pericellular sheath was particularly evident at the trailing edge but was excluded from the leading edge of PC3 cells. These studies indicate that prostate cancer cells recruit stromal components to remodel their pericellular environment and promote their motility.     

Conformational studies of polymers and copolymers of L-aspartate esters. I. Preparation and solution studies

An alcoholysis method is described for the modification of high molecular weight poly(β-benzyl L -asparatate); by this method the benzyl groups in the polypeptide have been replaced by methyl, ethyl, isopropyl, n-propyl, and phenethyl groups to give a series of copolymers of each of the corresponding aspartate esters with benzyl L -aspartate. By repeating the reactions, replacement of better than 99% has been achieved in some cases to give in effect the homopolymer. Optical rotatory dispersion studies show that of all the systems studied only poly(β-methyl L -aspartate) has the left-handed helix sense, the others are right-handed. It is shown further that the helix sense is not an intrinsic property of the nature of the aspartate side chain. Raising the temperature of chloroform solutions of the right-handed form of the copolymers of benzyl L -aspartate and ethyl L -aspartate results in a transition to the left-handed helix, the temperature of the transition being dependent on the composition of the copolymer. Also poly(β-n-propyl L -aspartate) undergoes a transition from the right- to the left-handed helix form at 59°C. These results suggest a general pattern of behavior of poly(aspartate esters) and that with suitable conditions of solvent and temperature they may be in either the right- or left-handed helical form.     

Clockwise and counterclockwise pinwheel colony morphologies of Bacillus subtilis are correlated with the helix hand of the strain

Helical macrofiber-producing strains of Bacillus subtilis grown on fresh complex medium semisolid surfaces formed "pinwheel"-shaped colonies. Clockwise pinwheel projections arose from colonies of strains that produce right-handed helical macrofibers in fluid cultures. Most strains able to make left-handed helical macrofibers in fluid grew as disorganized wavy colonies without directed projections. A phage-resistant left-handed mutant was found that produces very tight colonies with pinwheel projections that lie counterclockwise relative to the colony. The pinwheel colony morphology is interpreted therefore in terms of the cell surface organization and helical growth.     

Left-handed Helical Polynucleotides with D-Sugar Phosphodiester Backbones

Naturally occurring polynucleotides have right-handed helical confrontations in the solid state¹ and in solution². Poly(dI-dC)poly(dI-dC) was found to form a left-handed helix in spite of the D-sugar backbone. Also, L-adenylyl-(3′–5′)-L-adenosine synthesized by Tazawa et al⁴. takes up the left-handed stacked conformation. We had synthesized a dinucleoside monophosphate, 8,2′-anhydro-8-mercapto-9-β-D-arabinofuranosyladenine phosphoryl-(3′–5′)-8,2′-anhydro-8-mercapto-9-β-D-arabinofuranosyladenine (A^spA^s) (molecular structure Ia; see also ref. 5) and this compound has a left-handed stacked conformation. The two bases in Ia, having the D-sugar backbone, stacked along the left-handed helical axis; these bases are fixed at ?_CN = ?108° (syn-anti region) by the anhydro linkages.