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Journal of Bacteriology, September 2000, p. 5218-5224, Vol. 182, No. 18
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
The Flagellar Filament of Rhodobacter
sphaeroides: pH-Induced Polymorphic Transitions and Analysis of
the fliC Gene
Deepan S. H.
Shah,1,2
Tania
Perehinec,3
Susan M.
Stevens,4
Shin-Ichi
Aizawa,2 and
R. Elizabeth
Sockett5,*
Microbiology Unit, Biochemistry Department,
University of Oxford, Oxford OX1 3QU,1
School of Biological Sciences, Sutton Bonnington Campus,
University of Nottingham, Sutton Bonnington, Leicestershire LE12
5RD,3 and Immunology
Division4 and Institute of
Genetics,5 University of Nottingham, Queens
Medical Centre, Nottingham NG7 2UH, United Kingdom, and
Department of Bioscience, Teikyo University, 1-1 Toyosatodai, Utsunomiya 320, Japan2
Received 22 December 1999/Accepted 20 June 2000
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ABSTRACT |
Flagellar motility in Rhodobacter sphaeroides is
notably different from that in other bacteria. R. sphaeroides moves in a series of runs and stops produced by the
intermittent rotation of the flagellar motor. R. sphaeroides has a single, plain filament whose conformation
changes according to flagellar motor activity. Conformations adopted
during swimming include coiled, helical, and apparently straight forms.
This range of morphological transitions is larger than that in other
bacteria, where filaments alternate between left- and right-handed
helical forms. The polymorphic ability of isolated R. sphaeroides filaments was tested in vitro by varying pH and ionic
strength. The isolated filaments could form open-coiled, straight,
normal, or curly conformations. The range of transitions made by the
R. sphaeroides filament differs from that reported for
Salmonella enterica serovar Typhimurium. The sequence of
the R. sphaeroides fliC gene, which encodes the flagellin
protein, was determined. The gene appears to be controlled by a
28-dependent promoter. It encodes a predicted peptide of
493 amino acids. Serovar Typhimurium mutants with altered polymorphic
ability usually have amino acid changes at the terminal portions of
flagellin or a deletion in the central region. There are no obvious
major differences in the central regions to explain the difference in polymorphic ability. In serovar Typhimurium filaments, the termini of
flagellin monomers have a coiled-coil conformation. The termini of
R. sphaeroides flagellin are predicted to have a lower
probability of coiled coils than are those of serovar Typhimurium
flagellin. This may be one reason for the differences in polymorphic
ability between the two filaments.
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INTRODUCTION |
Bacteria swim through liquids by
means of a propeller-like, rotating flagellum (23). The
major component of the flagellum is the long, extracellular filament, a
polymer of flagellin protein. The antigenicity of flagellin, its
variability, its property of self-assembly into filaments, and the ease
with which it may be purified have resulted in an extensive study of
these proteins and the gene(s) encoding them in many bacterial genera
(reviewed in reference 15). Electron microscopic
studies have revealed two distinct types of filaments called
"plain" and "complex" (32). Plain filaments have a
smooth appearance, whereas complex filaments have ridges and grooves on
the surface (32, 38, 39). Most bacteria including
Salmonella possess plain filaments. Complex filaments have
been observed for three species of soil bacteria: Pseudomonas
rhodos (32), Sinorhizobium meliloti
(10), and Sinorhizobium lupini (33).
Previously, it was suggested that filament type might correlate with
the mode of flagellar rotation. Bacteria with plain filaments can
switch their rotation from clockwise (CW) to counterclockwise, whereas
bacteria with complex filaments can rotate their flagella only in the
CW direction and do not switch direction of rotation but stop rotation
periodically (so-called unidirectional, intermittent rotation
[11]). Complex flagella are brittle and form
left-handed helices with little or no structural polymorphism
(11). Plain filaments are flexible and have distinct polymorphic forms with different helical characteristics. Filaments rotating in the counterclockwise direction (swimming cells) are normally left-handed helices (normal shape), and a change in direction of rotation to CW (tumbling cells) converts them into right-handed helices (curly shape [24]). This polymorphic ability
is required for the swimming and tumbling of bacterial taxis.
Plain filaments can also be induced to change shape in vitro
(polymorphic transitions) by changing environmental conditions such as
pH, temperature, salt concentration, organic solvent, viscous flow, or
sugar concentrations (18, 34). Although it is not clear
whether such transitions have a physiological effect on swimming
behavior in the wild, they may be a useful way of modulating motility
under different conditions in the absence of tactic stimuli. A
comparison of the amino acid sequences from plain filament flagellin
proteins of many species reveals a relatively high degree of
conservation in the amino- and carboxyl-terminal regions, whereas the
central regions are very variable even between flagellins from
different strains of the same species (8, 14, 15).
A notable deviation from the correlation between filament types and
mode of flagellar rotation is seen in the purple, nonsulfur, aquatic
bacterium Rhodobacter sphaeroides (37). Each cell
has a single plain filament but displays unidirectional, intermittent flagellar rotation. Moreover, the filament can take on at least three
distinct polymorphic forms in vivo: a normal structure while rotating,
an apparently straight form during fast rotation, and an unusual,
loosely coiled conformation during a stop. Detached filaments with the
former and latter polymorphic forms can also be observed (2,
3). In light of these interesting differences between R. sphaeroides and other species, we chose to study the filament of
this organism in greater detail. In this paper, we describe polymorphic
forms of the filament induced in vitro by changes in pH and ionic
strength. We also report sequence analysis and expression studies of
the fliC gene, which encodes the flagellin protein of this organism.
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MATERIALS AND METHODS |
Strains, plasmids, and media.
The bacterial strains and
plasmids used in this work are described in Table
1. Growth media and antibiotic selection
were as described previously (35). Motility analysis was
carried out by direct observation of exponentially growing cells by
phase-contrast microscopy or by point inoculation of semisolid agar
(0.3% [wt/vol] agar, 0.03% [wt/vol] yeast extract, 0.03%
[wt/vol] NaCl, 0.03% [wt/vol] tryptone) to test for swarming.
Isolation of flagella and observation of filament
polymorphs.
A modified version of the method of Aizawa and
coworkers (1) was used for the large-scale isolation of
intact flagella for R. sphaeroides. Photosynthetic culture
(1.5 liters) at an optical density at 660 nm of 0.75 was harvested, and
the cells were lysed and treated with DNase as described previously
(1). The pH was increased to 10 by the dropwise addition of
5 M NaOH in order to eliminate contaminating membrane fragments.
Cellular debris was removed by centrifugation at 15,000 rpm for 45 min in Beckman JA 21 rotor. Flagella were collected from the supernatant by
centrifugation at 30,000 rpm for 30 min in a Beckman L7
ultracentrifuge. The flagellar pellet was resuspended in TET buffer (10 mM Tris-HCl [pH 8], 1 mM EDTA, 0.1% [wt/vol] Triton X-100). A
density gradient was set up by the addition of 0.43 g of CsCl per
ml of suspension and centrifugation at 20,000 rpm at 14°C overnight
in a Beckman L7 ultracentrifuge. The flagella formed a cloudy white
band, which was collected. CsCl was removed by a wash in 4 volumes of
TET buffer. The final pellet was resuspended in 0.5 ml of TET buffer. The flagella were observed by high-intensity dark-field microscopy. Broken, detached flagellar filaments were also harvested from stationary-phase cultures by a 30-min 30,000-rpm centrifugation step
and CsCl gradient (as detailed above). These were also used in
polymorphic studies to preclude any effects of flagellar basal bodies
(present in the intact preparation) on filament polymorphisms.
The buffers for observations of filament polymorphism at pH 2 to 8 were
prepared with citric acid and Na
2HPO
4 as
described
previously (
6). A second set of buffers from pH 7 to 11 were
prepared by mixing 12.5 ml each of 0.2 M Tris and 0.2 M
glycine.
The pH was adjusted with either 0.2 M HCl or 0.1 M NaOH before
deionized water was added to a final volume of 50 ml. In all cases,
an
appropriate volume of 5 M NaCl was added to give the desired
concentration of NaCl. Equal volumes of buffer and flagellar solution
were mixed and incubated at room temperature for 5 min before
observation by high-intensity dark-field microscopy. The results
were
recorded on
videotape.
Recombinant DNA techniques.
Recombinant DNA techniques were
carried out as described by Sambrook and coworkers (31).
Restriction and modification enzymes were obtained from Northumbria
Biochemicals, New England Biolabs, and Boehringer Mannheim. DNA
fragments were purified using the Geneclean kit (Bio 101), and the
Photogene detection kit (Life Technologies) was used for Southern
blotting. R. sphaeroides genomic DNA isolations, DNA
sequencing, and conjugation protocols for complementation analysis were
as described previously (7, 27, 35).
Western blotting.
Sodium dodecyl sulfate-polyacrylamide gel
electrophoresis of whole cells or sheared filaments was carried out
according to the method of Laemmli as described by Sambrook and
coworkers (31). Sheared filaments were prepared from motile
bacterial cultures by 10 passages through a 3FG cannulum (Portex UK)
held between two 10-ml syringes. The proteins from the gels were
transferred to Hybond-C super nitrocellulose (Amersham) for 1 h at
a constant 100 mA. After being blocked overnight in PBS-T (140 mM NaCl,
2.7 mM KCl, 10 mM Na2HPO4, 1.8 mM
KH2PO4, 0.3% [vol/vol] Tween 20), containing
1% (wt/vol) milk (Marvel nonfat dried milk), the membrane was washed
in PBS-T for 5 min. It was incubated in a 1/1,000 dilution of antiserum
raised against R. sphaeroides flagellar filaments (36) in PBS-T, containing 1% (wt/vol) milk and 15%
(wt/vol) bovine serum albumin for 2 h. The membrane was washed
three times with PBS-T, containing 0.3% (wt/vol) milk, and then
incubated with a 1/1,000 dilution of anti-rabbit immunoglobulin
G-alkaline phosphatase conjugate (Sigma) in PBS-T containing 0.3%
(wt/vol) milk. After five washes in phosphate-buffered saline, the blot was developed by incubation in detection buffer (2.5 mg of
5-bromo-4-chloro-3-indolylphosphate [BCIP] ml
1, 5 mg of
nitroblue tetrazolium ml1, 100 mM Tris-HCl [pH 9.5],
100 mM NaCl, 5 mM MgCl2) until color development was
observed. The reaction was stopped by washing the blot in excess water.
Bioluminescence measurements.
Stationary-phase, nonmotile,
photosynthetic cultures (30-ml volume) were diluted by mixing them with
70 ml of fresh medium to introduce flagellar gene expression. Samples
were taken immediately and then every hour. Readings for light emission
were taken on a Turner luminometer. The light intensity per unit of
cell mass was calculated by dividing the luminometer reading by the
optical density of the culture sample at 600 nm.
Nucleotide sequence accession number.
The DNA sequence was
submitted to EMBL under accession no. Y14687.
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RESULTS |
Polymorphic ability of detached R. sphaeroides
flagella.
Figure 1 is a phase
diagram of the dominant forms observed under different conditions of pH
and ionic strength. Four forms for R. sphaeroides filaments
could be distinguished: straight, normal, open coils, and curly.
Examples are illustrated in Fig. 2. Both
intact flagella and broken detached filaments from R. sphaeroides gave the same results. The normal, straight, and
curly types resembled morphological types previously observed for the Salmonella filament (17). The coiled structures,
seen in this study and by Armitage and Macnab (2), are
referred to as "open coils" because they are distinct from the
coiled forms of Salmonella filaments observed by Kamiya and
Asakura (16). The difference is that the diameter of the
R. sphaeroides open coils is greater and the
Salmonella coil appears as a long cylinder when viewed from
the side whereas no such structures were visible for the R. sphaeroides open coils. They were found to resemble rope lasso structures rather than cylinders.
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FIG. 1.
Phase diagram showing the predominant polymorphic forms
of isolated R. sphaeroides flagellar filaments in
buffers of different pHs and ionic strengths.
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FIG. 2.
High-intensity dark-field microscope images of typical
polymorphic forms of R. sphaeroides flagella. (A)
Straight; (B) normal with some open coils; (C) open coils; (D) curly
(the inset shows greater magnification of the curly form). The open
coils and the normal forms were faint and highly susceptible to
Brownian motion, and therefore it was difficult to obtain good
micrographs of these from the videotape; some examples are shown.
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Interestingly, the dominant form under physiological conditions is the
open-coil form, which was also observed for cells with
stopped flagella
(
2,
3). This is in contrast to
Salmonella i-flagella, which have a predominantly normal conformation, which
undergoes a transition to curly at pH values lower than 4 in the
presence of 0.1 M NaCl (
16).
As found previously for
Salmonella filaments
(
16), the lines drawn between the types of
Rhodobacter filament conformations
in Fig.
1 are not firm
boundaries. In many cases, different morphological
types could coexist
under the same conditions (Fig.
2B), and the
lines represent boundaries
where one form becomes dominant over
all others. When normal filaments
were the predominant forms,
a small proportion of open coils and
straight forms were observed.
The curly and straight forms were never
observed together. At
pH values lower than 3, the filaments were no
longer visible owing
to the depolymerization of the filament into
flagellin monomers.
Prolonged incubation (>15 min) at pH 3 also
resulted in depolymerization,
and this effect was enhanced with
increasing NaCl
concentration.
The range of forms obtained for the
R. sphaeroides
filament is different from that obtained for the
Salmonella
filament by
Kamiya and Asakura (
16). In order to determine
whether this
is a result of gross differences between the amino acid
sequences
of the flagellin proteins of the species, the
fliC
gene of
R. sphaeroides was cloned and sequenced as
described
below.
Cloning, sequencing, and expression of R. sphaeroides
fliC.
The R. sphaeroides fliC gene was isolated by
complementation of a nonmotile, filament-minus TnphoA
mutant, R. sphaeroides Nm15 (37), with a
clone from a wild-type R. sphaeroides cosmid library.
Two kilobases of wild-type DNA from the cosmid clone that flanked the
site of TnphoA insertion in the mutant was localized by
Southern hybridization and sequenced on both strands. It was found to
encode one long open reading frame (ORF) starting at nucleotide 241, just after the HincII site (Fig.
3) and ending at nucleotide 1722. Eleven
bases upstream from the ATG start codon was the sequence AGGAGGG,
which matches the consensus sequence for ribosome-binding sites
in bacteria (9, 20). Upstream from that was a potential
promoter region with a version of the 28 consensus
sequence TAAA(N14)GCCGTTGA. The DNA sequence was submitted to EMBL (accession no. Y14687), and the predicted amino acid sequence
from the ORF was used to search the EMBL database. The R. sphaeroides ORF showed homology with numerous flagellin
proteins, particularly flagellins from the plain flagella of
Bacillus subtilis (43% identity), Escherichia
coli and Salmonella enterica serovar Typhimurium (36%
identity), and Pseudomonas aeruginosa (41% identity) (Fig.
4). The amino acid sequence of R. sphaeroides flagellin, in common with those of other bacteria,
lacks cysteine and tryptophan (S. meliloti FlaA and FlaB are
the only ones that contain tryptophan), but it is unusual that it also
lacks proline. R. sphaeroides flagellin has very low
homology with the S. meliloti flagellins FlaA (27% identity) and FlaB (24% identity) from complex flagella. These low
levels of homology are not unexpected given that R. sphaeroides has plain flagella and that the unidirectionality
of flagella from both species is likely due to motor and not filament
properties, although 16S ribosomal DNA phylogenies show that S. meliloti and R. sphaeroides are closely related.
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FIG. 3.
Map of the region encoding R. sphaeroides
FliC. The putative 28 promoter region and the site of
cloning of the luxCDEAB reporter cassette used in expression
studies are shown.
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FIG. 4.
Prettybox multiple sequence alignment of R. sphaeroides FliC (flic_rsph) with FliCs from enteric and soil
bacteria. For reasons of space, much of the variable central region is
not shown. The regions predicted to form coiled coils are shown using
serovar Typhimurium coordinates (heavy bars) or R. sphaeroides coordinates (dotted line). Accession numbers are
as follows: S. meliloti FlaA (flaa_rhime), P13118; S. meliloti FlaB (flab_rhime), P13119; P. aeruginosa FlaA
(flaa_pseae), P21184; B. subtilis FliC (flic_bacsu), P02868;
serovar Typhimurium FliC (flic_salty), P06179; E. coli FliC
(flic_ecoli), P04949.
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To test for promoter activity, in the 600-bp region upstream from the
fliC ORF, a transcriptional fusion containing a promoterless
Photorhabdus luminescens luxCDABE cassette (
41)
was constructed.
The cassette from pSB390 (G. S. A. B. Stewart and M. Winson, unpublished
data) was cloned as a 5.8-kb
BamHI fragment into the
BglII site
of the
fliC gene in plasmid pRK415 to give pTP11. A second plasmid,
pSB395 (
41), which contains the
lux cassette in
the same orientation
and same vector as pTP11 but without any
R. sphaeroides DNA, was
used as a background control. The
bioluminescence levels of
R. sphaeroides WS8N cultures,
containing each plasmid, were monitored
over a time course after
dilution from stationary phase (as detailed
in Materials and Methods).
The results are shown in Fig.
5. It
is
clear that the region upstream from the
fliC ORF has
promoter
activity in
R. sphaeroides. Interestingly,
although the (wild-type)
R. sphaeroides WS8N cells
containing pSB395 were motile, the cells
containing pTP11 were
nonmotile throughout the experiment, although
the growth rates of the
two were similar (data not shown). There
are two possible reasons for
this: (i) significant overexpression
of the products of the
lux genes somehow interferes with motility,
or (ii) the
promoter fragment of the plasmid sequesters some essential
transcription factor(s) and prevents or reduces expression of
chromosomally encoded
fliC. The only identifiable promoter
consensus
in the upstream 600-bp region is a sequence similar to the
28-dependent promoters of other species (Fig.
6), and so it may
be
28
that is sequestered by the plasmid-borne promoter. Plasmid pTP11,
containing the
R. sphaeroides fliC promoter region, did
not give
luminescence activity in
E. coli (data not shown).
This may be
due to slight differences between the
28
consensus in
R. sphaeroides and that in
E. coli (Fig.
6) (
n =
14 bases and penultimate base
is G in
R. sphaeroides,
n = 15 bases
and
penultimate base is A in
E. coli).
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FIG. 5.
Promoter activity of the region upstream from the
fliC ORF as indicated by the luxCDEAB reporter
system. OD600, optical density at 600 nm.
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FIG. 6.
Consensus 28 recognition sequences
compared to the putative promoter sequence of R. sphaeroides
fliC. The B. subtilis 28 is also known
as D, and that of E. coli is known as
F (4, 12, 21).
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To test whether the polymorphic, plain filament
R. sphaeroides flagellin could substitute for the flagellin in
E. coli plain
filaments, the
R. sphaeroides
fliC gene was cloned into pUC19
such that it was under the control
of the
lac promoter. This plasmid,
named pKa, was introduced
into two nonmotile
fliC mutants of
E. coli,
YK4146 and YK4516.
R. sphaeroides fliC failed to
complement
the
E. coli mutations, and although
R. sphaeroides FliC protein
was detectable by Western blotting in
the cytoplasm of
E. coli,
it was not present in sheared
fractions or in the medium (data
not shown). This result prevented us
from studying any polymorphic
properties of hybrid
E. coli-R.
sphaeroides flagella. It appears
that the
R. sphaeroides flagellin may not be exported by the
E. coli flagellar export
system.
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DISCUSSION |
The flagellar filament of R. sphaeroides
shows an interesting range of polymorphic transitions under varying
conditions of pH and ionic strength in vitro. Although the curly,
normal, and straight shapes are also seen with Salmonella
filaments (16, 17), the open-coil form is, as a naturally
occurring form, unique to R. sphaeroides filaments. The
open-coil form is the most common under physiological conditions and is
distributed across a broad range of conditions. Interestingly, in vivo,
stopped flagella have an open-coil shape whereas fast-rotating flagella
have a normal helical or apparently straight shape (2, 3).
It is thought that slow rotation of the coiled flagellum after a stop facilitates cell reorientation (3). This ability to change direction is essential during a tactic response since R. sphaeroides cells are unable to tumble in the manner of
bacteria with switching flagella. Thus, it appears that the filament of
R. sphaeroides has intrinsic properties that allow
polymorphic transitions adapted to the mode of swimming.
In serovar Typhimurium, mutations that affect the polymorphic ability
of the filament are found to cause amino acid substitutions in the
highly conserved N- and C-terminal regions of flagellin (19)
and flagellins with small deletions at either terminus are also
affected in their polymorphic ability (40). Direct interactions within the termini of flagella are important for the
polymorphic ability of the flagellar filament (25). Thus, terminal portions of flagellin are a determinant for polymorphic ability in serovar Typhimurium. In addition, a deletion in the variable
central domain of serovar Typhimurium flagellin also resulted in
alteration of polymorphic ability of the filament, possibly because a
change in the overall charge of the region altered repulsive or
attractive forces between subunits (26, 43). Such studies
suggest that a combination of interactions between the ordered termini
at the filament core and interactions between the outer domains of
flagellin molecules is responsible for polymorphic changes.
In order to test whether the differences in polymorphic abilities of
the filaments from R. sphaeroides and serovar
Typhimurium were reflected in differences at the molecular level, the
flagellin sequences of these two organisms were compared. The
hydropathy profiles of the two proteins are similar throughout, despite
the divergence of the R. sphaeroides sequence in the
central, nonconserved domain (data not shown). The terminal regions of
both proteins are predicted to have an alpha-helical character. The
serovar Typhimurium flagellin forms coiled-coil structures at the
termini (13, 28, 42). We analyzed both flagellins using the
COILS program (22) (Fig. 7).
As expected, serovar Typhimurium flagellin is predicted to have coiled
coils close to either terminus whereas R. sphaeroides
flagellin has a much lower probability of coiled coils in these
regions. This difference may be the key reason for the different
polymorphic abilities of filaments from these two species.
Interestingly, most of the mutations affecting polymorphic ability in
serovar Typhimurium flagella (19) map within, or close to,
these regions. Furthermore, many of these mutant sequences are
predicted to have altered coiled-coil probabilities compared to the
wild-type sequence according to the COILS program (data not shown).
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FIG. 7.
Prediction of coiled-coil structures at the termini of
flagellin proteins. The predictions were carried out using the COILS
program (22) with a window size of 28 residues. Solid line,
serovar Typhimurium FliC; dashed line, R. sphaeroides
FliC.
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The overall amino acid compositions of the nonconserved central regions
of FliCs (corresponding to amino acids 204 to 292 of serovar
Typhimurium), which comprise the outer domains in the assembled
flagellar filament, are similar in flagellins of R. sphaeroides and Salmonella. Therefore, the
intersubunit interactions in the outer parts of the filaments of these
species might be expected to be similar. This general assertion does
not seem to be borne out by the differences that we observed in
filament polymorphisms for the two bacteria. Mimori-Kiyosue and
coworkers (26) have found that the outer domain (D3) plays a
significant role in determining the polymorphic abilities of serovar
Typhimurium flagellar filament. It is possible that the central domain
plays no role in the differences in polymorphic ability seen here, or
subtle changes involving just a few amino acids in the D3 domain of
R. sphaeroides flagellin, rather than the overall amino
acid composition, are responsible for altered intersubunit interactions
that account for the unusual polymorphic abilities of R. sphaeroides flagellar filaments. It would be interesting to
exchange the central domains of Salmonella and R. sphaeroides flagellins and test whether the resulting
filaments had altered polymorphic abilities.
We have discussed some features that may be responsible for the
polymorphic properties of the R. sphaeroides filament.
The R. sphaeroides FliC is predicted to differ in its
secondary structure at the termini from the serovar Typhimurium
flagellin. It is also possible that a few key amino acid changes in the
nonconserved region of R. sphaeroides FliC cause changes
in intersubunit interactions. It would be interesting to see if these
predictions are borne out by a detailed structural study of the
R. sphaeroides filament.
It is difficult to speculate on the biological significance of the
unusual properties of the R. sphaeroides filaments. It is likely that the properties of the filament are adapted to its mode
of swimming motility, which in turn is adapted to its environment. R. sphaeroides inhabits aquatic or terrestrial
environments, whereas serovar Typhimurium is found mainly in intestinal
mucous surfaces. It may be that tumbling facilitates directional
changes in highly viscous mucous surfaces whereas in relatively
low-viscosity aquatic environments a combination of Brownian motion and
slow rotation of the filament open coil is sufficient to achieve a
change in orientation. Thus, the flagellar filaments of the two species may be adapted to these different requirements. Additionally, for
R. sphaeroides, having a single flagellum, which forms a
coil close to the cell body when stopped, may reduce the risk of being caught by protozoal predators in the wild. The single flagellum presents only a single receptor site for protozoa like
Acanthamoeba which bind to bacterial flagella
(30). There could be other explanations for the unusual
properties of R. sphaeroides FliC that will be
illuminated by a greater understanding of its natural history in the wild.
This study has provided some interesting insights into the properties
of the R. sphaeroides flagellum and a comparison of it
with the well-studied serovar Typhimurium flagellum. Understanding polymorphic transitions in different flagella and how they vary with
the chemical environment sheds light on the nature of FliC subunit
interactions in filaments. Such knowledge may have implications for the
design of nanofilaments with predictable physical properties.
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ACKNOWLEDGMENTS |
This work was supported by grant no. F.114L from the Leverhulme
Trust to R.E.S. and by a Royal Society study visit grant to D.S.H.S.
and a BBSRC ISIS study visit grant to R.E.S. S.M.S. was supported
by an EC technical training scheme.
We thank Takuya Gotou for assistance with image processing and members
of the Aizawa and Sockett labs for useful discussions.
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FOOTNOTES |
*
Corresponding author. Mailing address: Institute of
Genetics, University of Nottingham, Queens Medical Centre, Nottingham NG7 2UH, United Kingdom. Phone: 44-115-9194496. Fax: 44-115-9709906. E-mail: liz.sockett{at}nottingham.ac.uk.
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G. E. Dean,
C. J. Jones,
R. M. Macnab, and S. Yamaguchi.
1985.
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J. Bacteriol.
161:836-849[Abstract/Free Full Text].
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| 2.
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Armitage, J. P., and R. M. Macnab.
1987.
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Abstract
Introduction
