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Zemer Gitai

Publications and source records attributed to Zemer Gitai.

11 recordsLinked to original sources
PubMed2026

Cell-body curvature reduces stall frequency to enhance Vibrio cholerae swimming and chemotaxis through hydrogels.

The swimming motility of the bacterial pathogen Vibrio cholerae is a virulence factor that aids in breaching the mucus layer. V. cholerae has a curved cell shape, and previous work demonstrated that loss of curvature decreases infectivity. Here, we investigate the mechanism by which curvature affects single-cell motility. We compared the chemotactic performance of wild-type curved cells and straight mutants. The two exhibit similar swimming properties in liquid and viscous solutions but differ significantly in mucus-mimicking hydrogels, where curved cells demonstrate an 86% increase in chemotactic drift. Trajectory analysis indicates comparable swimming speeds, but straight mutants experience more frequent stalls, reducing total swimming time. Stalls further reduce chemotactic performance by imposing an average reorientation down the chemical gradient, regardless of cell shape. Coarse-grained molecular dynamics simulations corroborate these results across intestinal mucus hydrogel stiffnesses and identify an optimal curvature for movement through hydrogel-like meshes, close to the pathogen's median curvature. These findings highlight cell shape's role in pathogenicity and the need to study bacterial behaviors under conditions more closely mimicking the host environment.

Vibrio cholerae↗
PubMed2006

Diversification and specialization of the bacterial cytoskeleton.

The past decade has witnessed the identification and characterization of bacterial homologs of the three major eukaryotic cytoskeletal families: actin, tubulin and intermediate filaments. These proteins play essential roles in organizing bacterial subcellular environments. Recently, the ParA/MinD superfamily has emerged as a new bacterial cytoskeletal class, and imaging studies hint at the existence of even more, as yet unidentified, cytoskeletal systems. Much as the cytoskeleton is used for different purposes in different eukaryotic cells, the specific identities, functions and regulatory mechanisms of cytoskeletal proteins can vary between different bacterial species. In addition, extensive cross-talk between bacterial cytoskeletal systems may represent an important mode of cytoskeletal regulation. These themes of diversity, species-specificity and crosstalk are emerging as central properties of cytoskeletal biology.

Actins↗
PubMed2006

Single molecules of the bacterial actin MreB undergo directed treadmilling motion in Caulobacter crescentus.

The actin cytoskeleton represents a key regulator of multiple essential cellular functions in both eukaryotes and prokaryotes. In eukaryotes, these functions depend on the orchestrated dynamics of actin filament assembly and disassembly. However, the dynamics of the bacterial actin homolog MreB have yet to be examined in vivo. In this study, we observed the motion of single fluorescent MreB-yellow fluorescent protein fusions in living Caulobacter cells in a background of unlabeled MreB. With time-lapse imaging, polymerized MreB [filamentous MreB (fMreB)] and unpolymerized MreB [globular MreB (gMreB)] monomers could be distinguished: gMreB showed fast motion that was characteristic of Brownian diffusion, whereas the labeled molecules in fMreB displayed slow, directed motion. This directional movement of labeled MreB in the growing polymer provides an indication that, like actin, MreB monomers treadmill through MreB filaments by preferential polymerization at one filament end and depolymerization at the other filament end. From these data, we extract several characteristics of single MreB filaments, including that they are, on average, much shorter than the cell length and that the direction of their polarized assembly seems to be independent of the overall cellular polarity. Thus, MreB, like actin, exhibits treadmilling behavior in vivo, and the long MreB structures that have been visualized in multiple bacterial species seem to represent bundles of short filaments that lack a uniform global polarity.

Actins↗
PubMed2005

Two independent spiral structures control cell shape in Caulobacter.

The actin homolog MreB contributes to bacterial cell shape. Here, we explore the role of the coexpressed MreC protein in Caulobacter and show that it forms a periplasmic spiral that is out of phase with the cytoplasmic MreB spiral. Both mreB and mreC are essential, and depletion of either protein results in a similar cell shape defect. MreB forms dynamic spirals in MreC-depleted cells, and MreC localizes helically in the presence of the MreB-inhibitor A22, indicating that each protein can form a spiral independently of the other. We show that the peptidoglycan transpeptidase Pbp2 also forms a helical pattern that partially colocalizes with MreC but not MreB. Perturbing either MreB (with A22) or MreC (with depletion) causes GFP-Pbp2 to mislocalize to the division plane, indicating that each is necessary but not sufficient to generate a helical Pbp2 pattern. We show that it is the division process that draws Pbp2 to midcell in the absence of MreB's regulation, because cells depleted of the tubulin homolog FtsZ maintain a helical Pbp2 localization in the presence of A22. By developing and employing a previously uncharacterized computational method for quantitating shape variance, we find that a FtsZ depletion can also partially rescue the A22-induced shape deformation. We conclude that MreB and MreC form spatially distinct and independently localized spirals and propose that MreB inhibits division plane localization of Pbp2, whereas MreC promotes lengthwise localization of Pbp2; together these two mechanism ensure a helical localization of Pbp2 and, thereby, the maintenance of proper cell morphology in Caulobacter.

Bacterial Proteins↗
PubMed2005

The new bacterial cell biology: moving parts and subcellular architecture.

Recent advances have demonstrated that bacterial cells have an exquisitely organized and dynamic subcellular architecture. Like their eukaryotic counterparts, bacteria employ a full complement of cytoskeletal proteins, localize proteins and DNA to specific subcellular addresses at specific times, and use intercellular signaling to coordinate multicellular events. The striking conceptual and molecular similarities between prokaryotic and eukaryotic cell biology thus make bacteria powerful model systems for studying fundamental cellular questions.

Bacteria↗
PubMed2005

MreB actin-mediated segregation of a specific region of a bacterial chromosome.

Faithful chromosome segregation is an essential component of cell division in all organisms. The eukaryotic mitotic machinery uses the cytoskeleton to move specific chromosomal regions. To investigate the potential role of the actin-like MreB protein in bacterial chromosome segregation, we first demonstrate that MreB is the direct target of the small molecule A22. We then demonstrate that A22 completely blocks the movement of newly replicated loci near the origin of replication but has no qualitative or quantitative effect on the segregation of other loci if added after origin segregation. MreB selectively interacts, directly or indirectly, with origin-proximal regions of the chromosome, arguing that the origin-proximal region segregates via an MreB-dependent mechanism not used by the rest of the chromosome.

Actins↗
PubMed2005

The choreographed dynamics of bacterial chromosomes.

Despite decades of study, the exquisite temporal and spatial organization of bacterial chromosomes has only recently been appreciated. The direct visualization of specific chromosomal loci has revealed that bacteria condense, move and position their chromosomes in a reproducible fashion. The realization that bacterial chromosomes are actively translocated through the cell suggests the existence of specific mechanisms that direct this process. Here, we review bacterial chromosome dynamics and our understanding of the mechanisms that direct and coordinate them.

Bacillus subtilis↗
PubMed2004

An actin-like gene can determine cell polarity in bacteria.

Achieving proper polarity is essential for cellular function. In bacteria, cell polarity has been observed by using both morphological and molecular markers; however, no general regulators of bacterial cell polarity have been identified. Here we investigate the effect on cell polarity of two cytoskeletal elements previously implicated in cell shape determination. We find that the actin-like MreB protein mediates global cell polarity in Caulobacter crescentus, although the intermediate filament-like CreS protein influences cell shape without affecting cell polarity. MreB is organized in an axial spiral that is dynamically rearranged during the cell cycle, and MreB dynamics may be critical for the determination of cell polarity. By examining depletion and overexpression strains, we demonstrate that MreB is required both for the polar localization of the chromosomal origin sequence and the dynamic localization of regulatory proteins to the correct cell pole. We propose that the molecular polarity inherent in an actin-like filament is translated into a mechanism for directing global cell polarity.

Actins↗
PubMed2003

The netrin receptor UNC-40/DCC stimulates axon attraction and outgrowth through enabled and, in parallel, Rac and UNC-115/AbLIM.

Netrins promote axon outgrowth and turning through DCC/UNC-40 receptors. To characterize Netrin signaling, we generated a gain-of-function UNC-40 molecule, MYR::UNC-40. MYR::UNC-40 causes axon guidance defects, excess axon branching, and excessive axon and cell body outgrowth. These defects are suppressed by loss-of-function mutations in ced-10 (a Rac GTPase), unc-34 (an Enabled homolog), and unc-115 (a putative actin binding protein). ced-10, unc-34, and unc-115 also function in endogenous unc-40 signaling. Our results indicate that Enabled functions in axonal attraction as well as axon repulsion. UNC-40 has two conserved cytoplasmic motifs that mediate distinct downstream pathways: CED-10, UNC-115, and the UNC-40 P2 motif act in one pathway, and UNC-34 and the UNC-40 P1 motif act in the other. Thus, UNC-40 might act as a scaffold to deliver several independent signals to the actin cytoskeleton.

Actin Cytoskeleton↗