Fluorescently labelled engineered Caulobacter crescentus cells and S-layer signal profiles, Herdman and coauthors2024figure1
Scientific organism fluorescence microscopy figure

Fluorescently labelled engineered Caulobacter crescentus cells and S-layer signal profiles, Herdman and coauthors2024figure1

Matthew Herdman, Buse Isbilir, Andriko von Kügelgen, Ulrike Schulze, Alan Wainman and Tanmay A. M. Bharat,2024, Cell cycle dependent coordination of surface layer biogenesis in Caulobacter crescentus, Nature Communications, doi:10.1038/s41467-024-47529-5, figure1; unchanged publisher figure · CC BY 4.0 · Image source

The micrographs show engineered Caulobacter crescentus cells labelled to compare existing and newly incorporated surface-layer material. Magenta and green encode fluorescent markers, not natural bacterial colors. The authors filtered the images to reduce noise; the surrounding plots quantify signal location in dividing and non-dividing cells.

Overview

Caulobacter crescentus is a bacterial model for cell growth, polarity and division. Its life cycle includes a non-dividing swarmer stage and a division-competent stalked stage. A protein surface layer, or S-layer, covers the cell and its stalk outside the outer membrane. This layer is formed from repeating RsaA proteins arranged in a hexagonal lattice and anchored through lipopolysaccharide. A 2024 investigation used modified laboratory cells to follow where newly produced material enters this covering.

Researchers labeled existing surface material with one fluorescent marker and subsequently added a differently colored marker during growth. The approach distinguished old and new regions rather than treating all surface fluorescence as equivalent. Short, non-dividing cells predominantly added material at their poles, while dividing cells showed conspicuous addition around the middle. Previously incorporated lattice remained comparatively stationary relative to the cell. The results connect surface renewal with changing cell geometry and growth stage, rather than describing a covering that is assembled once and then remains unchanged.

Drug perturbations helped separate related processes. Disrupting cell division with cephalexin or mitomycin C did not abolish the distinct localization of newly added surface material. In contrast, treatment affecting the cytoskeletal protein MreB or the lipopolysaccharide component disrupted that pattern. MreB inhibition also changes several cellular processes and strongly alters shape, so the observations do not identify a single isolated signaling pathway. The persistence of an ordered lattice in some disrupted cells further distinguishes loss of normal localization from complete failure to form surface protein.

Additional labeling of peptidoglycan linked new cell-wall material with later surface-layer addition at division regions. Electron cryotomography revealed discontinuities and overlapping lattice sheets near these growth sites. The authors propose that expanding cell-envelope regions create gaps where available RsaA molecules can enter the lattice. This is a mechanistic model supported by the combined observations, not direct tracking of every proposed molecular step. The study did not localize the RsaA secretion machinery, and whether higher-level coordination acts beyond envelope expansion remains unresolved.

The examined material expressed a SpyTag-bearing RsaA variant in a specified laboratory background. Fluorescence measurements and reconstructed tomograms therefore document that experimental system. They offer a route to investigating how a growing cell maintains an ordered exterior, without establishing that all bacterial surface layers solve the same geometric problem or that Caulobacter represents the original ancestral cell envelope.

Swarmer and stalked stagesHexagonal RsaA surface latticeCell-cycle-dependent surface renewalPolar stalk growth
01

Origins & earliest records

Source-specific account centered on Herdman and colleagues’ 2024 surface-layer study, not an original taxonomic description.

02

Evidence & interpretation

Pulse-chase fluorescence, cell-wall labeling, chemical perturbations and electron cryotomography distinguish observed insertion patterns from the proposed gap-filling model.

Selected bibliography

Documented works and useful reading. This is not a list of every appearance.

  1. 01

    Cell cycle dependent coordination of surface layer biogenesis in Caulobacter crescentus

    Matthew Herdman, Buse Isbilir, Andriko von Kügelgen, Ulrike Schulze, Alan Wainman and Tanmay A. M. Bharat · 2024

    Nature Communications 15, 3355; complete main Results, Discussion and Methods. Experimental CB15N ΔsapA rsaA467:SpyTag background; CC BY 4.0 adaptation credited.

  2. 02

    Complete genome sequence of Caulobacter crescentus

    William C.Nierman and colleagues · 2001

    PNAS98(7):4136–4141; online20March/issue27March2001; DOI10.1073/pnas.061029298.

Family, evolution & connections

Selected Caulobacteraceae genome representatives (Hallgren et al., 2025)

Six named genome representatives selected from Supplementary Figure S1, the fully labelled version of Figure 1a. Other Caulobacterales, five alphaproteobacterial outgroups and most family members are omitted. These samples do not represent every species in each genus.

  • Selected Caulobacteraceae samples
    • Selected Asticcacaulis / Brevundimonas branch
      • Asticcacaulis excentricus CB 48
      • Brevundimonas diminuta ATCC 11568
    • Other selected family branch
      • Poindextera montana S6
      • Selected Caulobacter and sister branch

Hallgren and colleagues manually curated 72 single-copy alphaproteobacterial marker genes, including checks for paralogy, contamination and possible horizontal transfer. Their 25,448-amino-acid concatenation was analysed in IQ-TREE with LG+C60+F+R and a posterior mean site-frequency approximation, using 100 non-parametric bootstrap replicates. This diagram preserves branching among selected tips; supports and branch lengths are not transcribed or recomputed. A sampled genome-based species hypothesis, not a direct-ancestor chain or a map of individual gene transfers. The paper labels CB15 as Caulobacter vibrioides [C. crescentus]; the laboratory-model profile remains linked with that explicit historical naming convention. Acaudatibacter aquilonius is an uncultured genome representative. The 2026 addendum supplies effective-publication protologues and corrects a SeqCode accession without revising this topology. Adapted from Hallgren et al. (2025), CC BY 4.0: six tips retained, intervening omitted branches suppressed, layout redrawn and original support/length/environment panels omitted.

Hallgren et al. (2025), Figure 1a, Supplementary Figure S1, focal phylogenetic Results and complete species-phylogeny Methods · Hallgren et al. (2026), Addendum: effective-publication protologues and SeqCode correction · Creative Commons Attribution 4.0 licence

Taxonomic classification

A hierarchy of classified groups, not a chain of direct ancestors.

  1. GenusCaulobacter
  2. SpeciesCaulobacter crescentus
Documented · ecological connection

Bacteriophages phiCbK and phiCb13

Guerrero-Ferreira and colleagues studied infection of Caulobacter strains by these two phages. Their microscopy and adsorption assays support initial contact through phage head filaments around bacterial flagella, followed by attachment near polar pili. Flagellar motion improved adsorption efficiency, but its absence did not make the tested bacteria wholly resistant. This is a laboratory host–phage relationship, not a branching genealogy.

Guerrero-Ferreira et al. (2011), flagellar machinery and pilus Results; infection-efficiency Methods
Documented · evolutionary relationship

Phenylobacterium immobile and sampled Acaudatibacter lineages

Hallgren and colleagues compared these relatives with the dimorphic Caulobacter model. Their phylogeny and genome annotations support separate losses of flagellar and developmental genes in Phenylobacterium immobile and a sampled Acaudatibacter clade. P. immobile’s symmetric reproduction was additionally tested by time-lapse microscopy; equivalent cellular behavior in uncultured Acaudatibacter remains an inference. Shared gene losses do not make either lineage a descendant of living C. crescentus.

Hallgren et al. (2025), convergent-loss Results, genome annotation and species-phylogeny Methods; CC BY 4.0

Located primary passages

Specific passages supporting details in this entry, grouped by their published witness.

Complete genome sequence of Caulobacter crescentus

PNAS98(7):4136–4141; online20March/issue27March2001; DOI10.1073/pnas.061029298.

  1. The report describes a circular chromosome of4,016,942 bases and3,767 predicted genes for CB15. Sequence comparisons identify extensive signaling and nutrient-scavenging candidates. Many proposed functions and gene-transfer explanations remain inferences; sequence availability did not itself complete the cell-cycle regulatory network. Comparisons claiming exceptionally numerous signaling proteins are dated to genomes available in2001.

    Complete main introduction, Methods, General Features, regulatory/adaptation/phylogeny sections and Conclusion; strainCB15.

Supplementary analyses and cited experiments unread; no sequence reanalysis or current taxonomic reassignment inferred.

References

Sources supporting this profile. Linked pages have their own scope and editorial standards.

  1. ResearchHerdman et al. 2024, primary surface-layer study (CC BY 4.0)Research access: 2026-10-05

Image credits

Scientific organism fluorescence microscopy figure

Fluorescently labelled engineered Caulobacter crescentus cells and S-layer signal profiles, Herdman and coauthors2024figure1

Matthew Herdman, Buse Isbilir, Andriko von Kügelgen, Ulrike Schulze, Alan Wainman and Tanmay A. M. Bharat,2024, Cell cycle dependent coordination of surface layer biogenesis in Caulobacter crescentus, Nature Communications, doi:10.1038/s41467-024-47529-5, figure1; unchanged publisher figure · CC BY 4.0 · Image source

The micrographs show engineered Caulobacter crescentus cells labelled to compare existing and newly incorporated surface-layer material. Magenta and green encode fluorescent markers, not natural bacterial colors. The authors filtered the images to reduce noise; the surrounding plots quantify signal location in dividing and non-dividing cells.

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