Caulobase

History

How a pond bacterium became a model cell

Caulobacter was first studied for its odd shape: a cell on a stalk. It became a model organism because every division is asymmetric, which makes the bacterial cell cycle visible: what happens, where in the cell, and in what order. Each milestone below links to the paper behind it.

  1. 1930s

    1. 1935

      Henrici & Johnson name the genus Caulobacter

      In a study of freshwater stalked bacteria, Henrici and Johnson proposed the genus Caulobacter ('stalked rod'), with C. vibrioides as type species, in J. Bacteriol. 30:61–93.

      Henrici & Johnson 1935 source source

  2. 1960s

    1. 1962

      Stove & Stanier: differentiation in stalked bacteria

      Stove and Stanier reported on cellular differentiation in stalked bacteria in Nature. Shapiro's 1971 review cites their work, with Poindexter's, as the start of Caulobacter differentiation studies.

      Stove & Stanier 1962 source

    2. 1964

      Poindexter's review; Caulobacter crescentus named

      Poindexter's Bacteriological Reviews monograph on the biology and classification of the Caulobacter group is the effective publication of the species name Caulobacter crescentus.

      Poindexter 1964 source source

  3. 1970s

    1. 1971

      Caulobacter proposed as a model for differentiation

      Shapiro, Agabian-Keshishian and Bendis presented Caulobacter as a model for prokaryotic differentiation: synchronizable cultures, a polar flagellum and stalk, and a phage-adsorption assay to follow the cycle.

      Shapiro et al. 1971 source

    2. 1977

      Density-gradient synchrony; strain NA1000

      Evinger and Agabian introduced a Ludox density-gradient method for isolating large quantities of synchronous cells. NA1000, the synchronizable derivative of CB15 used by most laboratories since, is attributed to this work by Marks et al. (2010).

      Evinger & Agabian 1977; Marks et al. 2010 source source

  4. 1990s

    1. 1992

      Cell-cycle control of the chromosomal origin

      Marczynski and Shapiro isolated the C. crescentus replication origin. A plasmid relying on it replicated with a cell-cycle timing resembling the chromosome's, implying closely linked cis-acting control elements.

      Marczynski & Shapiro 1992 source

    2. 1993

      Proteins have addresses: polar chemoreceptors

      Alley, Maddock and Shapiro found new chemoreceptors at the nascent swarmer pole and their targeted proteolysis during differentiation; Maddock and Shapiro showed polar chemoreceptor clusters in E. coli.

      Alley et al. 1993; Maddock & Shapiro 1993 source source

    3. 1994

      CcrM DNA methyltransferase

      Zweiger, Marczynski and Shapiro identified CcrM, which methylates adenine in GANTC sites and is expressed only just before division, so chromosomal sites shift from full to hemimethylation as DNA replicates.

      Zweiger et al. 1994 source

    4. 1995

      The flagellar gene hierarchy

      Shapiro's Cell review 'The bacterial flagellum: from genetic network to complex architecture' summarized how flagellum biogenesis is coordinated by a regulatory hierarchy of flagellar genes.

      Shapiro 1995 source source

    5. 1995

      Circuit simulation of genetic networks

      McAdams and Shapiro proposed modeling genetic networks with circuit simulation integrated with biochemical kinetics, illustrated with the phage lambda lysis-lysogeny circuit; an early systems-biology approach.

      McAdams & Shapiro 1995 source source

    6. 1996

      CtrA, an essential cell-cycle regulator

      Quon, Marczynski and Shapiro identified CtrA, an essential two-component response regulator controlling cell division, stalk synthesis and cell cycle-regulated transcription, including DNA replication and methylation genes.

      Quon et al. 1996 source

    7. 1997

      Stochastic mechanisms in gene expression

      McAdams and Arkin's simulations showed that proteins are made from an activated promoter in short random bursts, causing cell-to-cell timing differences and probabilistic outcomes in genetic switches.

      McAdams & Arkin 1997 source

    8. 1997

      Regulated proteolysis drives the G1-S transition

      Domian, Quon and Shapiro showed CtrA activity is set by cell type-specific phosphorylation and proteolysis; a stable, constitutively active CtrA blocked the G1-to-S transition.

      Domian et al. 1997 source

    9. 1998

      ClpXP protease is essential for the cell cycle

      Jenal and Fuchs showed that the ATP-dependent protease ClpXP is essential in Caulobacter and required for the cell-cycle-dependent degradation of CtrA; mutants arrest before chromosome replication starts.

      Jenal & Fuchs 1998 source

  5. 2000s

    1. 2000

      Cell-cycle transcriptome

      Laub et al. used microarrays on synchronized cells to find 553 genes (19% of the genome) whose mRNA varied with the cell cycle; CtrA was involved in controlling 26% of them. Later ChIP work found ≥95 direct CtrA targets.

      Laub et al. 2000; Laub et al. 2002 source source

    2. 2001

      Complete genome sequence

      Nierman et al. reported the C. crescentus genome: one circular chromosome of 4,016,942 bp encoding 3,767 genes, including 105 two-component signaling proteins.

      Nierman et al. 2001 source

    3. 2003

      Crescentin shapes the crescent

      Ausmees, Kuhn and Jacobs-Wagner described crescentin, an intermediate filament-like protein required for the curved shape of C. crescentus; without it cells grow as straight rods.

      Ausmees et al. 2003 source

    4. 2004

      Oscillating master regulators: GcrA and CtrA

      Holtzendorff et al. identified GcrA as a master regulator whose levels oscillate out of phase with CtrA, forming a circuit that times DNA replication and polar morphogenesis.

      Holtzendorff et al. 2004 source

    5. 2004

      Chromosomal loci have subcellular addresses

      Viollier et al. found that each of 112 chromosomal loci has a specific cellular position, arrayed in order along the cell, and that newly replicated loci move sequentially to their destinations during replication.

      Viollier et al. 2004 source

    6. 2006

      MipZ positions the division ring

      Thanbichler and Shapiro identified MipZ, which binds ParB at the segregating origins and inhibits FtsZ polymerization, restricting the division ring to midcell.

      Thanbichler & Shapiro 2006 source

    7. 2006

      Holdfast adhesion measured

      Tsang et al. measured detachment forces of 0.11–2.26 µN for single cells held by the holdfast and estimated >68 N/mm² adhesion strength, which they described as the strongest ever measured for biological adhesives.

      Tsang et al. 2006 source

    8. 2006

      CckA–ChpT phosphorelay controls CtrA

      Biondi et al. identified the phosphotransferase ChpT and showed that the kinase CckA drives phosphorelays that phosphorylate and stabilize CtrA, within a single integrated cell-cycle circuit with DivK feedback.

      Biondi et al. 2006 source

    9. 2007

      A whole-cell uranium biosensor

      Hillson et al. engineered C. crescentus to fluoresce in micromolar uranium using the uranium-responsive urcA promoter, and distinguished contaminated from clean groundwater samples from Oak Ridge.

      Hillson et al. 2007 source

    10. 2008

      PopZ organizes the cell pole

      Two groups identified PopZ: Bowman et al. showed it anchors the origin/ParB complex at the pole; Ebersbach et al. described it as a self-associating hub that organizes multiple polar functions.

      Bowman et al. 2008; Ebersbach et al. 2008 source source

  6. 2010s

    1. 2011

      The essential genome by Tn-seq

      Christen et al. combined hyper-saturated transposon mutagenesis with sequencing to map essential elements at 8-bp resolution: 1,012 features including 480 ORFs, 402 regulatory sequences and 130 non-coding elements.

      Christen et al. 2011 source

    2. 2013

      Mapping chromosome structure (5C and Hi-C)

      After 5C-based 3D models of the genome (Umbarger et al., 2011), Le et al. applied Hi-C and found the chromosome organized into multiple, largely independent spatial domains.

      Le et al. 2013; Umbarger et al. 2011 source source

    3. 2013

      Base-pair methylome through the cell cycle

      Kozdon et al. used SMRT sequencing at five cell-cycle time points to follow the methylation state of 4,515 GANTC sites, which moved from full to hemimethylation as replication forks advanced.

      Kozdon et al. 2013 source

    4. 2014

      Coding and noncoding genome architecture

      Schrader et al. combined ribosome profiling, RNA-seq, global 5'-RACE and mass spectrometry to map transcripts and translation start sites at near-complete coverage; most start codons lacked Shine-Dalgarno sites.

      Schrader et al. 2014 source

    5. 2015

      c-di-GMP as a cell-cycle oscillator

      Building on PleD, a polar diguanylate cyclase (2004), Lori et al. showed c-di-GMP binds the kinase CckA and switches it to phosphatase mode at the G1-S transition, driving replication.

      Lori et al. 2015; Paul et al. 2004 source source

    6. 2017

      How Caulobacter senses a surface

      Two Science papers: Ellison et al. found that resisting pilus retraction triggers holdfast synthesis; Hug et al. found the flagellar motor acts as a tactile sensor that stimulates c-di-GMP production.

      Ellison et al. 2017; Hug et al. 2017 source source

    7. 2018

      BR-bodies: bacterial RNA condensates

      Al-Husini et al. showed that Caulobacter RNase E assembles liquid-liquid phase-separated ribonucleoprotein bodies (BR-bodies) that act as sites of mRNA decay, analogous to eukaryotic P-bodies.

      Al-Husini et al. 2018 source

  7. 2020s

    1. 2020

      PopZ microdomain sequesters signaling proteins

      Lasker, von Diezmann et al. combined single-molecule tracking and modeling to show that the ~200 nm PopZ microdomain at the pole selectively concentrates phospho-signaling proteins, including the kinase CckA.

      Lasker et al. 2020 source

    2. 2022

      PopZ condensates: material state tunes function

      Lasker, Boeynaems et al. showed PopZ condensate material properties, from liquid to solid, tune function; Saurabh et al. showed ATP depletion promotes phase separation of these bacterial condensates.

      Lasker et al. 2022; Saurabh et al. 2022 source source

    3. 2025

      Caulobacter in evolutionary and ecological context

      Hallgren et al. compared hundreds of Caulobacterales species, finding widespread phototrophy genes and convergent loss of dimorphism traits among close relatives of C. crescentus.

      Hallgren et al. 2025 source

    4. 2025

      Lasker~Koshland Special Achievement Award to Shapiro

      Lucy Shapiro received the 2025 Lasker~Koshland Special Achievement Award in Medical Science, recognizing her discoveries on bacterial asymmetric division, Stanford's Developmental Biology department and national leadership.

      source