cell polarity; cell division; bacteria; FtsZ tubulin; protein kinase; oxidoreductase; muramidase; protein localization; regulation; cell fate; flagellum; asymmetric division
Mignolet J, Viollier PH (2011), A sweet twist gets Bacillus into shape, in Molecular Microbiology
, 80(2), 283-285.
Guerrero-Ferreira RC, Viollier PH, Ely B, Poindexter JS, Georgieva M, Jensen GJ, Wright ER (2011), Alternative mechanism for bacteriophage adsorption to the motile bacterium Caulobacter crescentus, in Proceedings of the National Academy of Sciences of the United States of America
, 108(24), 9963-9968.
Kirkpatrick CL, Viollier PH (2011), Decoding Caulobacter development, in FEMS Microbiology Reviews
, 36(1), 193-205.
Kirkpatrick CL, Viollier PH (2011), New(s) to the (Z-)ring, in Current Opinion in Microbiology
, 14(6), 691-697.
Kirkpatrick CL, Viollier PH (2011), Poles apart: prokaryotic polar organelles and their spatial regulation., in Cold Spring Harbor perspectives in biology
, 3(3), 1-10.
Davis NJ, Viollier PH (2011), Probing flagellar promoter occupancy in wild-type and mutant Caulobacter crescentus by chromatin immunoprecipitation, in FEMS Microbiology Letters
, 319(2), 146-152.
Kirkpatrick Clare L, Viollier Patrick H (2011), Reflections on a sticky situation: how surface contact pulls the trigger for bacterial adhesion., in Molecular microbiology
, 83(1), 7-9.
Radhakrishnan SK, Viollier P (2011), Two-in-one: bifunctional regulators synchronizing developmental events in bacteria, in Trends in Cell Biology
, 22(1), 14-21.
Kirkpatrick CL, Viollier PH (2010), A polarity factor takes the lead in chromosome segregation, in EMBO Journal
, 29(18), 3035-3036.
Many bacterial cells are intrinsically polarized. They exploit this feature to direct proteins to polar positions where they execute specialized functions. During division (binary fission) of a rod-shaped bacterial cell, two new poles are formed (one for each progeny). After division, each daughter cell features two poles that differ in age: one is the newborn pole that was just built by the cytokinetic apparatus containing the cell wall (peptidoglycan) synthesizing machinery, while the other is the preexisting (or ‘old’) pole from the mother cell that was inherited at division. This form of polar asymmetry/polarity in prokaryotes is widespread and critical for growth and division control, chromosome segregation, chemotaxis and polarized secretion of virulence factors. While deposition of certain proteins at one or both cell poles is a clear manifestation of polarity, how this is accomplished at the molecular level is poorly understood. Our recent data support the idea that the positional information reflecting polarity is imprinted on the new poles when they are born, i.e. during division. Since the cytokinetic apparatus is implicated in polarity, the molecular mechanism(s) of division control has attracted our interest. Our efforts have concentrated on illuminating the molecular underpinnings of bacterial cell polarity by elucidating the mechanism for the localization of selected proteins to the old or the new pole. Because this work will invariably unveil the molecular identity of determinants that govern polar specificity, it will educate us on the problem of how the old pole is discerned from the new one. The preeminent model system for studies on prokaryotic cell polarity is the Gram-negative a-proteobacterium Caulobacter crescentus, where the old and the new pole can easily be discriminated by light microscopy due to the presence of different appendages: a stalked organelle that is elaborated from the old pole and the flagellum that is mounted on the new pole. We are studying two complementary polar localization pathways in Caulobacter: i) that of the TipF flagellar assembly regulator that is placed at the new pole and ii) that of the cell-fate regulatory kinase DivJ that is localized to the old (stalked) pole. Our studies on the spatio-temporal regulation of these two markers and their pathways have recently converged on the process of cytokinesis (see below). On these grounds we propose a new research plan that is divided into three experimental topics (I-III) to illuminate the molecular mechanisms of polarity and division control in Caulobacter and their link(s). I. TipN, a polar positioning factor of flagella and TipF, is localized to the new pole and this localization requires its prior recruitment to the centrally placed cytokinetic apparatus organized by the tubulin-like division protein FtsZ (Cell, 2006). We will further explore the relationship between division and polarity by probing for physical associations of TipN/F with the cytokinetic machinery. We will also test if mutations in FtsZ can be isolated that compromise flagellar placement. And finally will try to induce flagellar misplacement by artificially tethering TipF to the old cell pole. II. We uncovered a localization factor, SpmX, for the recruitment and activation of the DivJ kinase at the old (stalked) pole. SpmX harbors a muramidase domain at the N-terminus that is necessary and sufficient for its own localization to the old pole. This domain is implicated in peptidoglycan binding, suggesting that SpmX recognizes a polar cell wall determinant (Genes Dev., 2008) that could be synthesized by the cytokinetic apparatus. We will test directly if SpmX binds the polar peptidoglycan and explore different models of localization by determining SpmX protein dynamics in live cells.III. Recently, we identified an oxido-reductase homolog, KidO, as a bi-functional regulator that enhances DivJ kinase activity and that plays an unanticipated role as a regulator of FtsZ (unpublished), a finding that reinforces the connection between cytokinetic and polarity pathways. We will investigate how KidO controls FtsZ activity in wild-type and mutant proteins and we will screen for and study other division regulators. Since FtsZ is a division protein that is conserved in eubacteria, several archaea and eukaryotic chloroplasts, elucidating the molecular mechanisms of division control and the ties to polarity should have broad implications for cellular biology in general.