Download Cytoskeletal elements in bacteria

Cytoskeletal elements in bacteria
Peter L Graumann
It has become clear recently that bacteria contain all of the
cytoskeletal elements that are found in eukaryotic cells,
demonstrating that the cytoskeleton has not been a eukaryotic
invention, but evolved early in evolution. Several proteins
that are involved in cell division, cell structure and DNA
partitioning have been found to form highly dynamic ring
structures or helical filaments underneath the cell membrane
or throughout the length of the cell. These exciting
findings indicate that several highly dynamic processes
occur within prokaryotic cells, during growth or
differentiation, that are vital for a wide range of
cellular tasks.
Addresses
Biochemie, Fachbereich Chemie, Hans-Meerwein-Straße,
Philipps-Universität Marburg, 35032 Marburg, Germany
e-mail: [email protected]
Current Opinion in Microbiology 2004, 7:565–571
This review comes from a themed issue on
Growth and development
Edited by Mike Tyers and Mark Buttner
Available online 27th October 2004
1369-5274/$ – see front matter
# 2004 Elsevier Ltd. All rights reserved.
DOI 10.1016/j.mib.2004.10.010
Abbreviations
FRAP
GFP
IF
fluorescence recovery after photobleaching
green fluorescent protein
intermediate filament
Introduction
In December 2003, our understanding of bacterial cytology was enriched by the discovery of another structural
element — the intermediate filament — in Caulobacter,
revealing that the bacterial cytoskeleton is far more
intricate than previously thought. All three known cytoskeletal elements in eukaryotes have now been identified
in bacteria, and all of them play important roles in diverse
cellular functions.
With the adaptation of cytological techniques, it has
become clear that bacteria possess an elaborate subcellular organization. Chromosomes are compacted into
nucleoids that are present in the central part of the cell
and have a defined arrangement, with each region having
a preferred position within the cell [1–3]. Ribosomes are
located in the cytosolic space surrounding the nucleoids,
www.sciencedirect.com
and thus are predominantly close to the cell poles,
whereas RNA polymerase is present on the nucleoids
themselves [4,5]. This general separation of transcription
and translation is a dynamic process that is dependent on
active transcription [6]. Replication, however, occurs at a
centrally located, stationary replication factory [7], such
that the chromosome moves through the replisome during replication, and duplicated regions on the chromosome are actively separated towards opposite cell poles by
an as yet unidentified motor [8]. The SMC (structural
maintenance of chromosomes) chromosome condensation complex localizes to one or two discrete foci on
the nucleoids, which is dependent on timing during
the cell cycle [9–11]. Several essential histidine kinases
localize to the cell poles at different times during the cell
cycle in Caulobacter crescentus [12] and the chemotactic
machinery is present at one or both cell poles in several
bacteria [13]. In addition, although bacterial cells can be
round, vibrio-shaped (crescents) or rod-shaped, all cells
divide in the middle to create two similar-sized daughter
cells, with the division machinery localizing to the middle
of the cells [14] in the form of a constricting ring. How is
this subcellular organization achieved? At least in some
cases, the clear answer is by way of cytoskeletal elements.
In this review, I highlight recent findings on cytoskeletal
elements and discuss their essential implications in cell
structure, division and DNA segregation.
Prokaryotic tubulin and its role in
cell division
In contrast to eukaryotic cells, which use actin (and
myosin) or other means, in the case of plants, for cell
division, bacteria generally employ the tubulin ortholog
FtsZ for this process [15]. FtsZ forms a ring structure in
the middle of the cell (slightly off-centre in C. crescentus)
(Figure 1a), and recruits all other known cell division
proteins to this site [14]. Jan Löwe’s group demonstrated
that FtsZ is a tubulin ortholog [16], which in eukaryotic
cells forms microtubules that provide cellular tracks for
organelle transport and that form the mitotic spindle
apparatus, among other functions. Like tubulin (a dimer
of a- and b-tubulin), FtsZ polymerises into hollow protofilaments (which can be straight or curved) as a result of
GTP binding (Figure 2a). Upon filament formation, GTP
appears to be rapidly hydrolysed into GDP and inorganic
phosphate [17]. The number of filaments that comprise
the Z ring is unclear but the ring has been shown recently
to be highly dynamic. Using FRAP (fluorescence recovery after photobleaching), the Erickson group showed
that the ring is completely remodelled within a timeframe of about 30 s (i.e. that polymerised FtsZ rapidly
Current Opinion in Microbiology 2004, 7:565–571
566 Growth and development
Figure 1
(a)
(b)
FtsZ-CFP
FtsZ-CFP
(d)
(c)
GFP-MreB
GFP-MreB/Nomarski
GFP-MreB/Nomarski
(e)
CreS (IF) / DAPI
Fluorescence microscopy of bacterial cells. (a) FtsZ (tubulin) forms a dynamic ring at the middle of growing cells to direct cell division.
B. subtilis cells expressing FtsZ-CFP (kind gift from P Lewis of Newcastle University, Australia) (b) After formation of a spiral intermediate
(indicated by an arrow), two FtsZ rings form at the onset of sporulation in B. subtilis cells, close to each cell pole. (c) MreB (actin) forms helical
filaments that move through the cell. These are growing B. subtilis cells expressing GFP-MreB. (d) MreB filaments are highly dynamic and
disintegrate within a few minutes after nutrient downshift (images (c) and (d) provided by H-J Defeu-Soufo of Marburg University).
(e) Crescentin forms a long filament at the concave side of the vibrio-shaped C. crescentus. Overlay of immunofluorescence-labelled
CreC (red) and DNA stain (blue; images courtesy of C Jacobs-Wagner of Yale University, USA). White lines indicate ends of cells,
which form long chains during exponential growth. White bar 2 mm.
exchanges with the non-polymerised pool within the cell)
[18]. Turnover of the polymers was found to correlate
with GTPase activity, suggesting that the FtsZ ring
consists of many bundles of protofilaments that continuously extend and shrink owing to the addition of GTPFtsZ and release of GDP-FtsZ. However, it remains to be
seen how the Z ring constricts, and thus, how cell division
is powered. There are several tubulin interacting proteins
in bacteria, which modulate the activity of FtsZ: actinlike FtsA protein, membrane protein ZipA (in Escherichia
coli and close relatives) and ZapA all stabilize Z rings
[19,20,21], while EzrA negatively controls FtsZ polymerisation in Bacillus subtilis [22]. All four proteins are
part of the division apparatus and localize as a ring to midcell, whereas the MinC protein inhibits FtsZ polymerisation close to the cell poles. MinC is recruited to the cell
Current Opinion in Microbiology 2004, 7:565–571
poles by MinD; their accumulation at the cell centre is
prevented by the MinE protein. The Min system is
highly dynamic in E. coli cells, with MinC and MinD
oscillating from pole to pole within seconds [23]. Both
proteins appear to form transient helical filaments [24],
the nature of which is still unclear.
When B. subtilis decides to differentiate into dormant
spores, for example, after deprivation of nutrients, the
cells divide asymmetrically into a large mother cell and a
small compartment that develops into the mature spore
[25]. At the onset of sporulation, the central Z-ring is
switched from mid cell to two rings close to each cell pole
(Figure 1b and Figure 3). Only one ring is chosen to form
a septum via a stochastic mechanism [26]. Switching of
the Z ring involves formation of spiral intermediates that
www.sciencedirect.com
Cytoskeletal elements in bacteria Graumann 567
Figure 2
(a)
GTP GTP
α– β–tubulin
+
(b)
ATP
–
GDP GDP
ATP
ADP
ATP
Strand 1
–
ADP
+
ATP
Strand 2
(c)
–
Current Opinion in Microbiology
Schematic drawing of the structure of microtubules, actin filaments and intermediate filaments. (a) Microtubules are formed by addition to the
plus end of a tubulin dimer, in which both subunits contain a bound GTP molecule. Upon binding, GTP in the b–subunit is hydrolysed.
Later hydrolysis of the GTP bound to the a-subunit destabilizes the polymer, leading to its dissociation, which can happen at both ends.
In eukaryotic cells, minus ends are usually stabilized by accessory proteins, such that plus ends perform growing or shrinking dynamics.
(b) Actin forms a double helix (both strands are identical in composition). ATP-bound actin adds to the plus end much more rapidly than
to the minus end, while minus ends can shrink as a result of polymer instability after ATP hydrolysis. Net growth at the plus end
and depolymerisation at the minus end could constitute a ‘treadmilling’ process, in which the filament appears to move.
(c) Intermediate filament-type proteins are rich in coiled coils and have an elongated structure. Formation of long polymers or
polymer sheets does not require any cofactor and is reversible, but upon covalent cross-linking of polymer subunits,
IFs become stable and can persist after cell death.
extend from mid-cell towards both cell poles (Figure 3),
due, at least in part, to a three-to-fourfold higher synthesis
of the FtsZ protein at the onset of sporulation, and also to
stabilization by the sporulation-specific SpoIIE phosphatase that exclusively localizes to the sporulation septum
[27]. Thus, a morphological switch in the bacterial tubulin ortholog induces an elaborate differentiation process.
Actin-like filaments as dynamic structures
that affect cell shape, chromosome
segregation and plasmids partitioning
By the late 1980s, it was already known that mutation of
the mreB gene leads to loss of rod-shape and to the
formation of round E. coli, Salmonella typhimurium or
B. subtilis cells [28]. Although the loss of the mreB gene
in E. coli causes only a drastic reduction in viability, mreB
is absolutely essential for viability in B. subtilis, Streptomyces coelicolor and in C. crescentus [29,30,31]. B. subtilis
contains two other MreB-like proteins, Mbl and MreBH,
the depletion of which leads to bent and distorted or
banana-shaped cells, respectively [31–33]. So clearly,
these proteins are important for the maintenance of proper cell shape and for viability. Strikingly, the Errington
www.sciencedirect.com
group found that MreB and Mbl form filamentous structures in B. subtilis cells, as revealed by immunofluorescence and GFP (green fluorescent protein) tagging to
visualize the proteins [31] (Figure 1c,d). Both filaments
formed helical structures underneath the cell membrane,
with Mbl filaments extending from pole to pole, while
MreB filaments appeared to be generally absent from
the poles. Additionally, the axial advance during one
complete revolution of the helix (the ‘pitch’ of the helix)
was measured to be much longer for Mbl filaments than
for the MreB structures. These data suggest that MreB
filaments control the width of the cell, whereas Mbl
filaments control the longitudinal axis of the cell [31].
Like MreB and Mbl, MreBH also forms helical filaments
(with properties that seem to lie midway between those of
MreB and Mbl filaments), which also influence straight
growth of cells [34]. Again, it was Jan Löwe’s group who
revealed the nature of the helical elements, by showing
that MreB is an actin ortholog [35]. MreB forms actin-like
double filaments — that is, two MreB strands running
in parallel, with the same orientation. These double
filaments are rather straight in the case of MreB, but
are helical in the case of actin (Figure 2b). ATP-actin
Current Opinion in Microbiology 2004, 7:565–571
568 Growth and development
Figure 3
minute [34]. Figure 4 shows a three-dimensional image
reconstruction of MreB filaments. The rate of movement
is at the lower end of that measured for actin in vivo and
in vitro [36], and could constitute a potential motor within
the cells, or a dynamic framework that orients subcellular
processes.
What is the function of these dynamic proteins? There
are several intricate connections between actins and the
cell envelope. Incorporation of new cell-wall material in
B. subtilis cells appears to follow a helical pattern that is
dependent on Mbl (but not on MreB) [39], suggesting
that actin-like filaments might direct cell-wall synthesis
to produce a rod shape. Also, several cell-wall synthesizing proteins localize, or appear to localize, in a helical
pattern underneath the cell wall in C. crescentus and in
B. subtilis, a process that is dependent on MreB in the
former cells, but is independent of MreB or Mbl in the
latter [29,40].
Current Opinion in Microbiology
Schematic illustration of morphological changes at the onset of
sporulation in B. subtilis cells. The central FtsZ ring forms spirals that
appear to be oriented towards both cell poles, as indicated by the
direction of arrowheads. Finally, two FtsZ rings form, one close to
each cell pole, and one forms an asymmetric septum, generating a
small compartment (the forespore) and the larger mother cell,
while the other ring dissipates.
monomers bind to the plus (‘barbed’) end of the filaments, while ATP hydrolysis occurs within the filament,
leading to net dissociation of ADP-actin from the negative (‘pointed’) end. Actin filaments can even move and
push, through polymerisation at one end and concomitant
de-polymerisation at the other end, a process termed
‘treadmilling’ [36]. Eukaryotic actin forms intracellular
microfilaments, which can be stabilized or branched by
accessory proteins to serve essential structural functions,
or can be highly dynamic, performing different motor
tasks [37]. Interestingly, MreB and Mbl have been found
to change their pattern of localization during the cell cycle
[29,38]. Using FRAP, the Errington group recently
demonstrated that Mbl filaments are dynamic structures
that rotate along the helical paths underneath the cell
envelope [38]. Time-lapse microscopy showed that,
indeed, many (apparently) bundles of MreB or Mbl
filaments move continuously and in parallel along helical
tracks, performing a full helical turn within about a
Current Opinion in Microbiology 2004, 7:565–571
However, it was shown recently that bacterial actin-like
proteins also play a role in the segregation of plasmids and
of whole chromosomes. In E. coli, the R1 plasmid localizes
to the middle of the cells, where it is replicated. ParR
protein binds to a cis site on the plasmids (parC) and
interacts with ParM, a plasmid-encoded actin-like protein
[41], which forms long filaments, carrying a plasmid at
their end [42,43]. By modulating ParM ATPase activity, ParR appears to direct the extension of the ParM
filaments, which drive the plasmid towards opposite cell
poles. Overproduction of an ATPase mutant of MreB in
E. coli or depletion of MreB in B. subtilis leads to a strong
defect in chromosome segregation [33,44]. In B. subtilis,
this is apparent even before a change in cell shape is
visible. Chromosome origins fail to be properly separated,
and because there are indeed cis-acting partitioning sites
on the B. subtilis or E. coli chromosomes [45,46], it seems
possible that extending MreB filaments might push the
replicated chromosomal sites apart. However, the filaments might also position or orient the central replication
machinery, or components of the segregation machinery.
The MreB-interacting protein SetB from E. coli is a
membrane protein that also localizes as traversing helical
loops and affects chromosome segregation [47], thus
providing another link between actin-like proteins and
chromosome dynamics. Depletion of MreB in C. crescentus
has also been shown to affect chromosome arrangement,
as well as localization of regulatory histidine kinases to
the proper cell pole [48]. It is clear that loss-of-function
of actin-like proteins has a highly pleiotrophic effect on
cell physiology.
Intermediate filament-like proteins
bend the cell
C. crescentus cells are vibrio-shaped, and owe this crescent
form to the CreS protein, which was found in a visual
screen for straight-growing cells [49]. CreS is a homolog
www.sciencedirect.com
Cytoskeletal elements in bacteria Graumann 569
Figure 4
(a)
(b)
Current Opinion in Microbiology
Three-dimensional view of actin filaments in B. subtilis cells (a) Three-dimensional image construction of GFP-MreB spirals, generated from
Z-sections taken through live cells. A single cell is rotated 908 around its axis, as indicated by the gray arrow, showing that MreB spirals
run along the inner side of the cell membrane, making full or half turns (indicated by a white or grey arrowhead, respectively).
The rotational view also shows that individual helices exist in the cells, which is illustrated in (b) as a cartoon.
of eukaryotic proteins that form intermediate filaments
(IFs) — 8–10 nm thick cytoskeletal elements that provide
internal mechanical support for the cell and position
different organelles (Figure 2c). CreS localizes in a filamentous form at the concave side of C. crescentus cells
(Figure 1e), and also forms a filament in stationary cells
that are highly elongated and helical [49]. CreS was also
found along the inner cell curvature along the whole
length of these helical cells. Thus, CreS filaments induce
bending of the cell, creating asymmetry along the cell
length. Similar to eukaryotic proteins forming IFs (such as
keratin, which provides mechanical strength in skin cells,
or vimentin in endothelial cells), CreS assembles into
10 nm-thick filaments and sheets, without any need for
co-factors or energy [49]. IF-type proteins are characterized by a high degree of coiled coils and a highly
elongated structure, and they reversibly assemble into
filaments that are covalently cross-linked to form meshworks, which persist even after the cell dies. Their
sequence conservation is low, so it is difficult to locate
them solely through sequence comparison. However, IFtype proteins are also present in Helicobacter pylori (a widespread inhabitant of human stomach) and in many other
bacterial species [49]. With the identification of CreS, it
has now been established that none of the three cytoskeletal elements within eukaryotic cells was a eukaryal
invention, and it will be interesting to investigate the role
and function of IF-type proteins in bacteria other than
Caulobacter.
chromosome segregation rather than for cell division,
while the opposite is true for the prokaryotic version,
and as actin drives cell division in many eukaryotic cells
but appears to play a major role in chromosome segregation in bacteria, it is clear that similar cytoskeletal components show a remarkable evolutional plasticity. The
presence of cytoskeletal elements in prokaryotes opens
up a whole new frontier that is amenable to powerful
genetics of microbial systems.
Several proteins move within bacterial cells — usually
along helical tracks, — an intriguing recurring theme that
is possibly driven through a treadmilling process. These
movements somehow orient other processes and polarize
cells. Future challenges in this field of moving structural
elements include the urgent need to find molecules that
interact with actin filaments and with IFs, both on the
cytosolic and the membrane side. Even the central division ring comprises highly dynamic filaments, which can
form helical filaments during an intermediate step in the
cell cycle, thus, it will be interesting to elucidate the
individual mechanisms of filament formation, movement
and orientation. It is anticipated that further research into
bacterial cytology will reveal many fundamental aspects
that are relevant for all types of cells, for example, the
mechanisms by which proteins find their defined subcellular address. The possibility of gaining a full understanding of such aspects underlines the future potential of
this field of research.
Conclusions
Bacteria possess a dynamic cytoskeleton that achieves a
variety of essential tasks, and that appears to have been
present in the ancestor of all cells. As tubulin is used for
www.sciencedirect.com
Update
It has been shown recently that FtsZ moves along helical
tracks in a subset of growing E. coli cells [50]. This is a
Current Opinion in Microbiology 2004, 7:565–571
570 Growth and development
novel example of directed movement of a cytoskeletal
element in bacteria.
Acknowledgements
Many more interesting publications on the bacterial cytoskeleton exist
but could not be cited, owing to length constraints. My thanks to
Peter Lewis, Christine Jacobs-Wagner and Hervé Joël Defeu Soufo for
providing stains and images, and to the editors for valuable comments.
Work in my laboratory is supported by the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen Industrie.
References and recommended reading
Papers of particular interest, published within the annual period of
review, have been highlighted as:
of special interest
of outstanding interest
1.
Teleman AA, Graumann PL, Lin DCH, Grossman AD,
Losick R: Chromosome arrangement within a bacterium.
Curr Biol 1998, 8:1102-1109.
2.
Niki H, Yamaichi Y, Hiraga S: Dynamic organization of
chromosomal DNA in Escherichia coli. Genes Dev 2000,
14:212-223.
3.
Viollier PH, Thanbichler M, McGrath PT, West L, Meewan M,
McAdams HH, Shapiro L: Rapid and sequential movement of
individual chromosomal loci to specific subcellular locations
during bacterial DNA replication. Proc Natl Acad Sci USA 2004,
101:9257-9262.
4.
Lewis PJ, Thaker SD, Errington J: Compartmentalization of
transcription and translation in Bacillus subtilis. EMBO J 2000,
19:710-718.
5.
Azam TA, Hiraga S, Ishihama A: Two types of localization of the
DNA-binding proteins within the Escherichia coli nucleoid.
Genes Cells 2000, 5:613-626.
6.
Mascarenhas J, Weber MHW, Graumann PL: Polar localization
of ribosomes in Bacillus subtilis depends on active
transcription. EMBO Rep 2001, 2:685-689.
7.
Lemon KP, Grossman AD: Localization of bacterial DNA
polymerase: evidence for a factory model of replication.
Science 1998, 282:1516-1519.
8.
Lemon KP, Grossman AD: Movement of Replicating DNA
through a Stationary Replisome. Mol Cell 2000, 6:1321-1330.
9.
Mascarenhas J, Soppa J, Strunnikov A, Grauman PL: Cell cycle
dependent localization of two novel prokaryotic chromosome
segregation and condensation proteins in Bacillus subtilis that
interact with SMC protein. EMBO J 2002, 21:3108-3118.
10. Lindow JC, Kuwano M, Moriya S, Grossman AD: Subcellular
localization of the Bacillus subtilis structural maintenance of
chromosomes (SMC) protein. Mol Microbiol 2002, 46:997-1009.
11. Ohsumi K, Yamazoe M, Hiraga S: Different localization of
SeqA-bound nascent DNA clusters and MukF-MukE-MukB
complex in Escherichia coli cells. Mol Microbiol 2001,
40:835-845.
12. Jacobs C, Domian IJ, Maddock JR, Shapiro L: Cell cycledependent polar localization of an essential bacterial histidine
kinase that controls DNA replication and cell division.
Cell 1999, 97:111-120.
13. Shapiro L, Losick R: Dynamic spatial regulation in the bacterial
cell. Cell 2000, 100:89-98.
14. Lutkenhaus J: Dynamic proteins in bacteria. Curr Opin Microbiol
2002, 5:548-552.
15. Amos LA, van den Ent F, Lowe J: Structural/functional
homology between the bacterial and eukaryotic
cytoskeletons. Curr Opin Cell Biol 2004, 16:24-31.
16. Lowe J, Amos LA: Crystal structure of the bacterial cell-division
protein FtsZ. Nature 1998, 391:203-206.
Current Opinion in Microbiology 2004, 7:565–571
17. Scheffers D-J, Driessen AJM: Immediate GTP hydrolysis upon
FtsZ polymerization. Mol Microbiol 2002, 43:1517-1521.
18. Stricker J, Maddox P, Salmon ED, Erickson HP: Rapid assembly
dynamics of the Escherichia coli FtsZ-ring demonstrated by
fluorescence recovery after photobleaching. Proc Natl Acad
Sci USA 2002, 99:3171-3175.
This report reveals that the FtsZ ring is a highly dynamic structure in which
microtubules constantly polymerise and depolymerise, in a manner that is
dependent on GTP hydrolysis.
19. Gueiros-Filho FJ, Losick R: A widely conserved bacterial cell
division protein that promotes assembly of the tubulin-like
protein FtsZ. Genes Dev 2002, 16:2544-2556.
Identification of a widely conserved bacterial protein that stabilizes FtsZ
rings during cell division.
20. Pichoff S, Lutkenhaus J: Unique and overlapping roles for ZipA
and FtsA in septal ring assembly in Escherichia coli. EMBO J
2002, 21:685-693.
21. Hale CA, Rhee AC, de Boer PA: ZipA-induced bundling of
FtsZ polymers mediated by an interaction between C-terminal
domains. J Bacteriol 2000, 182:5153-5166.
22. Haeusser DP, Schwartz RL, Smith AM, Oates ME, Levin PA: EzrA
prevents aberrant cell division by modulating assembly of the
cytoskeletal protein FtsZ. Mol Microbiol 2004, 52:801-814.
23. Hale CA, Meinhardt H, de Boer PA: Dynamic localization cycle
of the cell division regulator MinE in Escherichia coli.
EMBO J 2001, 20:1563-1572.
24. Shih YL, Le T, Rothfield L: Division site selection in Escherichia
coli involves dynamic redistribution of Min proteins within
coiled structures that extend between the two cell poles.
Proc Natl Acad Sci USA 2003, 100:7865-7870.
This work shows that Min proteins, which oscillate from pole to pole in
E. coli cells, also form helical filaments.
25. Rudner DZ, Losick R: Morphological coupling in development:
lessons from prokaryotes. Dev Cell 2001, 1:733-742.
26. Eichenberger P, Fawcett P, Losick R: A three-protein inhibitor of
polar septation during sporulation in Bacillus subtilis.
Mol Microbiol 2001, 42:1147-1162.
27. Ben-Yehuda S, Losick R: Asymmetric cell division in B. subtilis
involves a spiral-like intermediate of the cytokinetic protein
FtsZ. Cell 2002, 109:257-266.
An increase in synthesis of FtsZ and interaction with a membrane
phosphatase appears to mediate switching of FtsZ rings from mid-cell
to positions close to the cell poles, initiating the sporulation differentiation
process in B. subtilis.
28. Graumann PL, Defeu-Soufo H-J: An intracellular actin motor in
bacteria? Bioessays 2004, in press.
29. Figge RM, Divakaruni AV, Gober JW: MreB, the cell
shape-determining bacterial actin homologue, co-ordinates
cell wall morphogenesis in Caulobacter crescentus.
Mol Microbiol 2004, 51:1321-1332.
An intriguing link is discussed between cell wall-synthesizing enzymes
and the MreB actin-like protein in C. crescentus.
30. Burger A, Sichler K, Kelemen G, Buttner M, Wohlleben W:
Identification and characterization of the mre gene region
of Streptomyces coelicolor A3(2). Mol Gen Genet 2000,
263:1053-1060.
31. Jones LJ, Carballido-Lopez R, Errington J: Control of cell shape
in bacteria: helical, actin-like filaments in Bacillus subtilis.
Cell 2001, 104:913-922.
32. Abhayawardhane Y, Stewart GC: Bacillus subtilis possesses
a second determinant with extensive sequence similarity to
the Escherichia coli mreB morphogene. J Bacteriol 1995,
177:765-773.
33. Soufo HJ, Graumann PL: Actin-like proteins MreB and Mbl from
Bacillus subtilis are required for bipolar positioning of
replication origins. Curr Biol 2003, 13:1916-1920.
34. Defeu-Soufo H-J, Graumann PL: Dynamic movement of
actin-like proteins within bacterial cells. EMBO Rep 2004,
5:789-794.
www.sciencedirect.com
Cytoskeletal elements in bacteria Graumann 571
35. van den Ent F, Amos LA, Lowe J: Prokaryotic origin of the actin
cytoskeleton. Nature 2001, 413:39-44.
36. Mogilner A, Oster G: Polymer motors: pushing out the front and
pulling up the back. Curr Biol 2003, 13:R721-R733.
37. Upadhyaya A, van Oudenaarden A: Biomimetic systems
for studying actin-based motility. Curr Biol 2003,
13:R734-R744.
38. Carballido-Lopez R, Errington J: The bacterial cytoskeleton:
in vivo dynamics of the actin-like protein Mbl of
Bacillus subtilis. Dev Cell 2003, 4:19-28.
FRAP experiments provide evidence that Mbl filaments are not static, but
appear to rotate within the cells, showing that the actin cytoskeleton is a
dynamic structure.
39. Daniel RA, Errington J: Control of cell morphogenesis in
bacteria: two distinct ways to make a rod-shaped cell.
Cell 2003, 113:767-776.
A clever method of labeling nascent cell-wall synthesis reveals that this
occurs in a helical pattern in B. subtilis cells, and is defective in Mbldeficient cells. However, not all rod-shaped bacteria appear to use a
helical insertion mechanism, but instead employ growth at polar zones
that is derived from the division machinery.
40. Scheffers DJ, Jones LJ, Errington J: Several distinct localization
patterns for penicillin-binding proteins in Bacillus subtilis.
Mol Microbiol 2004, 51:749-764.
41. van den Ent F, Moller-Jensen J, Amos LA, Gerdes K, Lowe J:
F-actin-like filaments formed by plasmid segregation protein
ParM. EMBO J 2002, 21:6935-6943.
Plasmid partitioning protein ParM has an actin-like structure and forms
right-handed helical filaments that are highly similar to actin.
42. Moller-Jensen J, Jensen RB, Lowe J, Gerdes K: Prokaryotic DNA
segregation by an actin-like filament. EMBO J 2002,
21:3119-3127.
In vivo, ParM forms long filaments throughout E. coli cells containing R1
plasmids, which are dynamic and essential for plasmid segregation.
43. Moller-Jensen J, Borch J, Dam M, Jensen RB, Roepstorff P,
Gerdes K: Bacterial mitosis: ParM of plasmid R1
moves plasmid DNA by an actin-like insertional
polymerization mechanism. Mol Cell 2003,
12:1477-1487.
www.sciencedirect.com
A simple but highly elegant mitotic-like apparatus segregates R1 plasmid
in E. coli cells. Polymerization of ParM, and actin ortholog, pushes
plasmids apart into opposite cell halves, a process that is dependent
on the parC partitioning site and the parC-binding ParR protein.
44. Kruse T, Moller-Jensen J, Lobner-Olesen A, Gerdes K:
Dysfunctional MreB inhibits chromosome segregation in
Escherichia coli. EMBO J 2003, 22:5283-5292.
This work shows a link between actin like proteins and chromosome
segregation.
45. Kadoya R, Hassan AK, Kasahara Y, Ogasawara N, Moriya S:
Two separate DNA sequences within oriC participate in
accurate chromosome segregation in Bacillus subtilis.
Mol Microbiol 2002, 45:73-87.
46. Yamaichi Y, Niki H: migS, a cis-acting site that affects bipolar
positioning of oriC on the Escherichia coli chromosome.
EMBO J 2004, 23:221-233.
47. Espeli O, Nurse P, Levine C, Lee C, Marians KJ: SetB: an integral
membrane protein that affects chromosome segregation in
Escherichia coli. Mol Microbiol 2003, 50:495-509.
The membrane protein SetB is shown to affect chromosome segregation
and to interact with the MreB, providing a link between cell membrane,
actin-like proteins and chromosome dynamics.
48. Gitai Z, Dye N, Shapiro L: An actin-like gene can determine
cell polarity in bacteria. Proc Natl Acad Sci USA 2004,
101:8643-8648.
Depletion of MreB leads to a loss of localization of histidine kinases to the
proper cell pole.
49. Ausmees N, Kuhn JR, Jacobs-Wagner C: The bacterial
cytoskeleton: an intermediate filament-like function in cell
shape. Cell 2003, 115:705-713.
This report shows that IF-type proteins exist in bacteria. C. crescentus
CreS forms a filamentous structure along the inner curvature of the
vibrio-shaped cells, and is required for maintenance of the curved cell
shape.
50. Thamedar S, Margolin W: FtsZ exhibits rapid movement and
oscillation waves in helix-like patterns in Escherichia coli.
Curr Biol 2004, 14:1167-1173.
In a subset of E. coli growing cells, filaments of FtsZ move along helical
tracks, another striking example of movement of cytoskeletal elements in
prokaryotes.
Current Opinion in Microbiology 2004, 7:565–571