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Martin Thanbichler
Max Planck Research Group / PUMa
Martin Thanbichler
born 26.04.1973
Diplom (Biology), Ludwig-Maximilans-Universität München, 1998
Dr. rer. nat. (Microbiology), Ludwig-Maximilans-Universität München, 2002
Postdoc (Prokaryotic Cell Biology), Stanford University, 2002-2006
Head of the Max Planck Research Group „Prokaryotic Cell Biology“ at the
MPI Marburg, since 2007
Junior professor of Microbiology, Philipps-Universität Marburg, since 2008
Cellular differentiation and cell division in
bacteria
Bacteria have evolved an abundance of different life
cycles and cell shapes, but the mechanisms that underlie this diversity are largely unknown. The aim of our
group is to understand the molecular basis of cellular
differentiation and cell division in bacteria and to elucidate how the one-dimensional information of the genetic code is translated into defined spatial and temporal regulatory patterns. To address these questions, we
are using a combination of cell biological, biochemical,
biophysical, and genetic approaches. Our studies focus
on the model organism Caulobacter crescentus, a Gramnegative α-proteobacterium that is characterized by its
unique developmental cycle (Fig. 1). C. crescentus cells
can easily be synchronized and then be observed as they
progress synchronously through their developmental
program, which greatly facilitates the study of cell cycledependent processes. Moreover, owing to their asymmetric cell division, they represent an attractive model
for studying bacterial differentiation.
and lowest at the cell center. Our analyses showed that
MipZ has the ability to inhibit polymerization of the bacterial tubulin homologue FtsZ and, thereby, to prevent
the assembly of the so-called FtsZ ring, which forms the
foundation of the ring-shaped cell division apparatus. As
a consequence, cytokinesis is limited to the midcell region and, furthermore, only initiates once chromosome
segregation has started. MipZ is highly conserved among
α-proteobacteria, which suggests that it represents the
prototype of a new and widespread class of bacterial cell
division regulators.
Division site placement
A fundamental problem in cell biology is the proper temporal and spatial regulation of cell division. Our previous
work has revealed the existence of a novel mechanism
that is responsible for positioning of the cell division
plane in C. crescentus. At its heart lies the Walker
ATPase MipZ, which forms a dynamic complex with the
chromosome partitioning protein ParB at the chromosomal origin of replication (Fig. 2). Upon initiation of
DNA replication, the two newly synthesized origin regions are immediately re-decorated with the MipZ/ParB
complex and then positioned at the two opposite cell
poles. This generates an intracellular gradient of MipZ,
with its concentration being highest at the cell poles
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Fig. 1. The C. crescentus cell cycle. The C. crescentus swarmer
cell bears a polar flagellum and a single, replicationally quiescent chromosome. At a certain point in the cell cycle, the flagellum is shed and a stalk is formed at the previously flagellated
pole. Concomitantly, DNA replication and cell division are initiated. Cytokinesis then gives rise to a new G1-arrested swarmer
cell and to a stalked cell that immediately enters the next division cycle.
Martin Thanbichler
Max Planck Research Group / PUMa
to the monomeric state. Losing its affinity for DNA and
FtsZ, it starts to diffuse rapidly within the cell until it
returns to the ParB complex, thereby closing the cycle.
MipZ thus shares similarity with small GTPases, using
nucleotide binding and hydrolysis to transition between
functionally distinct conformational states.
Cell division
The bacterial cell division apparatus (divisome) comprises a variety of different proteins, whose precise function and mode of cooperation is still poorly understood.
Moreover, it is unclear to what extent the results obtained in the prototypic model system E. coli can be applied to evolutionarily distinct organisms. Recent work
suggests that a core of essential divisome components
is widely conserved among bacteria, whereas a number
of accessory factors are restricted to certain lineages or
a few species only.
Fig. 2. Placement of the cell division plane by the spatial regulator MipZ. See text for explanations.
The MipZ system provides the first example of a regulatory protein gradient in bacteria. Our current research
focuses on the molecular mechanisms responsible for
gradient formation. Using a combination of crystallographic, biochemical, and cell biological approaches,
we were able to demonstrate that MipZ undergoes a
dynamic localization cycle that is driven by differential
affinities of its ADP- and ATP-bound forms for ParB and
chromosomal DNA (Kiekebusch et al., unpublished).
In complex with ADP, MipZ exists as a monomer that
specifically interacts with the polar ParB complex. Upon
nucleotide exchange, MipZ dimerizes and becomes able
to bind unspecifically to DNA. As a consequence, it
leaves ParB and randomly attaches to nearby regions of
the nucleoid, with the frequency of MipZ-DNA complexes decreasing as a function of distance from the
cell pole. Only the ATP-bound form of MipZ is able to
interact with FtsZ, thus inhibiting FtsZ ring assembly
over the pole-proximal parts of the nucleoid. Owing to
its intrinsic ATPase activity, the dimer eventually hydrolyzes its nucleotide cofactor, and MipZ switches back
Based on sequence similarity searches, most core components of the E. coli divisiome have previously been
identified in C. crescentus. One of the exceptions was
FtsN, a peptidoglycan-binding protein that orchestrates
the activity of cell wall synthases and hydrolases involved
in cell wall invagination. Initially, the absence of this
protein was not surprising, given that FtsN was thought
to be a peculiarity of E. coli and its close relatives. However, we have now identified a C. crescentus protein that,
despite the lack of sequence conservation, shows the
structural and functional characteristics of FtsN and
thus likely represents a highly diverged FtsN homologue
(Möll & Thanbichler, 2009). Based on conserved features defined in our work, we were able to identify putative FtsN homologues in a large variety of species covering all proteobacterial lineages. Two of these candidate
proteins were further investigated and verified to be cell
division proteins, indicating that FtsN-like proteins are
widespread among bacteria, albeit highly variable at the
sequence level. We found that the peptidoglycan-binding (SPOR) domain of FtsN is dispensable for function
but required for robust localization to the division site.
Given that it is recruited to midcell in isolated form and
retains its localization potential in heterologous hosts, it
likely recognizes a conserved feature of the invaginating
cell wall. Hence, the SPOR domain is likely to drive a
positive feedback loop whereby only a small amount of
FtsN is recruited to the division site by direct interaction
with the divisome to initiate cell constriction. Synthesis
of new cell wall material may then generate an increasing number of additional binding sites for FtsN, thus
further accelerating the division process.
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Martin Thanbichler
Max Planck Research Group / PUMa
Fig. 3. Midcell localization of FtsN-like proteins in different
bacteria. Fluorescent protein fusions of FtsN-like proteins from
C. crescentus (α−proteobacteria), M. xanthus (δ-proteobacteria)
and B. thailandensis (β-proteobacteria) were visualized by differential interference contrast (DIC) and fluorescence microscopy.
tion. Yet a different situation is observed for Shewanella
oneidensis, whose single bactofilin homologue shows
the typical localization pattern of a cell division protein.
These findings indicate that bactofilins can adopt a wide
range of functions in the cell. Biochemical analyses revealed that bactofilins polymerize spontaneously in the
absence of additional cofactors in vitro, forming stable
ribbon- or rod-like filament bundles. These structures
might have evolved as an alternative to intermediate filaments, serving as versatile molecular scaffolds in a variety of cellular pathways.
Searching for interaction partners of FtsN, we have recently identified a peptidoglycan hydrolase, designated
DipM, that is required for proper invagination of the
cell wall during cytokinesis (Möll et al., unpublished).
On deletion of the dipM gene, the outer layers of the
cell envelope fail to follow the inner membrane during
constriction, thus uncoupling compartmentalization of
the cytoplasm from daughter cell separation. As a consequence, cells tend to form filaments or grow in chains,
with branches emerging from the poles of individual
cytoplasmic compartments. These results suggest that
constriction of the cell may occur by deposition of additional peptidoglycan layers at the inner face of the cell
wall and concomitant removel of the outer layers by lytic
enzymes such as DipM. Moreover, they underscore the
key role of FtsN in in the organization of peptidoglycan
remodeling at the division site.
Cytoskeletal elements
The cytoskeleton has a vital function in the temporal and
spatial organization of both prokaryotic and eukaryotic
cells. Our work has revealed the existence of a new class
of polymer-forming proteins, designated bactofilins, that
are widely conserved among bacteria (Kühn et al, 2009).
In C. crescentus, two bactofilin paralogues cooperate to
form a sheet-like structure that lines the cytoplasmic
membrane in proximity of the stalked cell pole. These
assemblies mediate polar localization of a peptidoglycan
synthase involved in stalk formation, thus complementing the function of the actin-like cytoskeleton and the
cell division machinery in the regulation of cell wall biogenesis. Myxococcus xanthus, by contrast, synthesizes
four bactofilin paralogues. Three of them are encoded in
an operon located in a cluster of motility-related genes,
assembling into a massive, rod-shaped structure that occupies the mid-third of the cell. Deletion of this operon
resulted in a severe defect in pilus-mediated gliding motility, suggesting direct or indirect involvement in locomo-
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Fig. 4. Structure and function of bactofilins in C. crescentus.
Polymers formed by the purified bactofilin homologue BacA
from C. crescentus were visualized by (A) DIC (bar: 10 µm) and
(B) transmission electron microscopy (bar: 75 nm). (C) Model for
the function of bactofilin sheets in C. crescentus. A membraneassociated bactofilin sheet interacts with the cytoplasmic tail
of the cell wall synthase PbpC, thereby targeting PbpC to the
stalked pole and promoting stalk biogenesis.
Cell polarity
In cooperation with Patrick H. Viollier (Case Western
Reserve University, Cleveland, Ohio), we have identified
a novel protein, SpmX, that plays a vital role in controlling the differential fate of stalked and swarmer cells in
C. crescentus (Radhakrishnan et al, 2008). SpmX is a
membrane protein that is targeted to the stalked pole
at the early predivisional stage of the cell cycle. Polar
localization is dependent on a periplasmic domain with
Martin Thanbichler
similarity to phage lysozymes, suggesting that the protein recognizes specific structural features of the polar
cell wall. SpmX acts as a targeting factor that tethers and
thereby activates the histidine kinase DivJ. Activated
DivJ, in turn, launches the stalked-cell-specific developmental program in the stalked sibling once cell division
has occurred. The swarmer cell, by contrast, lacks the
SpmX/DivJ complex and thus expresses a different set of
genes which encodes swarmer-specific functions.
Max Planck Research Group / PUMa
Finished theses
Diploma/MSc theses
Andrea Möll (2008) Auf den Spuren von FtsN – Studie
eines Zellteilungsproteins in Caulobacter crescentus.
Katja Leser (2008) CC1873 and CC3022 – Charakterisierung mutmaßlicher neuer Cytoskelett-Elemente
in Caulobacter crescentus.
Publications
Lin Yang Zhang (2008) Analyse der Rolle von ParB bei
der Regulation der Zellteilung in Caulobacter crescentus.
1. Kühn, J., Briegel, A., Mörschel, E., Kahnt, J., Leser,
K., Wick, S., Jensen, G.J., and Thanbichler, M. (2010).
Bactofilins, a ubiquitous class of cytoskeletal proteins
mediating polar localization of a cell wall synthase in
Caulobacter crescentus. EMBO J. 29, 327-339.
Kathrin E. Klein (2008) Die Rolle der Klasse A Penicillin-Bindeproteine bei der Morphogenese von Caulobacter crescentus.
2. Thanbichler, M. (2009). Synchronization of chromosome dynamics and cell division in bacteria. Cold Spring
Harb. Perspect. Biol. 2, a000331.
Anne Raßbach (2009) Untersuchungen zur Biologie des
Planctomyceten Gemmata obscuriglobus.
BSc theses
3. Thanbichler, M. (2009). Spatial regulation in Caulobacter crescentus. Curr. Opin. Microbiol. 12, 715-721.
Aljona Gutschmidt (2009) Biochemische Charakterisierung des Zellteilungsregulators MipZ aus Caulobacter crescentus.
4. Thanbichler, M. (2009). Closing the ring: a new twist
to bacterial chromosome condensation. Cell 137, 598600.
Nicole Schnaß (2009) Funktionelle Analyse von Proteinen der Zellwandbiosynthese in Caulobacter crescentus.
5. Möll, A., and Thanbichler, M. (2009). FtsN-like
proteins are conserved components of the cell division
machinery in proteobacteria. Mol. Microbiol. 72, 10371053.
6. Radhakrishnan, S.K., Thanbichler, M., and Viollier
P.H. (2008) The dynamic interplay between a cell fate
determinant and a lysozyme homolog drives the asymmetric division cycle of Caulobacter crescentus. Genes
Dev. 22, 212-225.
Structure of the group (12/2009)
Group leader: Jun.-Prof. Dr. Martin Thanbichler
PhD students: Andrea Möll, Daniela Kiekebusch,
Juliane Kühn, Anne Raßbach, Susan Schlimpert
MSc student: Alexandra Jung
BSc students: Oliver Leicht, Wolfgang Strobel
7. Thanbichler, M., and Shapiro, L. (2008) Getting organized – how bacteria move proteins and DNA. Nat. Rev.
Microbiol. 6, 28-40.
Technical assistant: Stephanie Wick
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Martin Thanbichler
Max Planck Research Group / PUMa
External funding
Address
Human Frontier Science Program: Young Investigator
Award (RGY 69/2008)
Jun.-Prof. Dr. Martin Thanbichler
Max-Planck-Institut für terrestrische Mikrobiologie
Karl-von-Frisch-Straße 10
35043 Marburg/Germany
Invited lectures
Jahrestagung der Vereinigung für Allgemeine und Angewandte Mikrobiologie, Frankfurt, Germany, Special
Group: Structure and Microscopy: „From micro- to
microscopical imaging in microbiology“ (9–11/3/2008)
162nd Meeting of the Society for General Microbiology, Edinburgh, Great Britain, Physiology, Biochemistry
& Molecular Genetics Group Session: “Prokaryotic cell
biology” (31/3–3/4/2008)
108th General Meeting of the American Society for
Microbiology, Boston, USA, Session 085: “Spatial
Regulation of Cytokinesis: From Bacteria to Eukaryotes” (1–5/6/2008)
8th Graduate Retreat of the MPI for Biochemistry,
Tegernsee, Germany (1–2/7/2008)
Fakultät für Biology, Bereich Mikrobiologie, LudwigMaximilians-Universität München (8/7/2008)
Departement für Chemie und Biochemie, Universität
Bern (8/12/2008)
Instituto de Biochimica Vegetal y Fotosintesis, CSIC/
Universidad de Sevilla, Spain (16/4/2009)
Lehrstuhl für Mikrobiologie/Organismische Interaktionen, Eberhard-Karls-Universität Tübingen, Germany
(28/5/2009)
Centre de Genetique Moleculaire, CNRS, Gif-surYvettes, France (20/11/2009)
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Phone: +49 6421 178-300
Fax: +49 6421 178-209
E-mail: [email protected]
Martin Thanbichler
Max Planck Research Group / PUMa
The Max Planck Research Group “Prokaryotic Cell Biology“. From left to right: Stephanie Wick, Oliver Leicht, Wolfgang Strobel,
Alexandra Jung, Martin Thanbichler, Juliane Kühn, Anne Raßbach, Andrea Möll, Susan Schlimpert, Daniela Kiekebusch
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