Stimulation of the <i>Caulobacter crescentus</i> surface sensing pathway by deletion of a specialized minor pilin-like gene
Bibliographic record
Abstract
ABSTRACT Bacteria colonize surfaces through complex mechanisms of surface sensing. Pili are dynamic bacterial appendages that play an important role in this process. In Caulobacter crescentus , the tension on retracting, surface-bound pili triggers the rapid synthesis of holdfast, an adhesive that permanently attaches cells to surfaces. However, the mechanosensory elements in pilus-mediated surface sensing remain unknown. In this study, we used a genetic screen to isolate mutants with altered pilus dynamics, to identify genes potentially involved in pilus-mediated surface sensing. This screen identified cpaL , whose deletion led to reduced piliation levels, but surprisingly also to increased holdfast production and attachment—an unexpected finding given the importance of pili in these processes. Interestingly, this phenotype was absent under conditions that restrict the surface-sensing pathway of holdfast production. Furthermore, when pilus retraction was blocked to artificially simulate surface contact, ∆ cpaL cells did not show increased holdfast production as seen in wild-type cells. Together, these observations suggest that loss of cpaL stimulates surface sensing even in the absence of mechanical cues, consistent with a negative regulatory role for CpaL in the surface-sensing pathway of holdfast production in C. crescentus . Structural predictions suggest that CpaL is a minor pilin fused to a mechanosensitive von Willebrand factor type A (vWA) domain, which can be accommodated at the pilus tip alongside other minor pilins. These results collectively position CpaL as a strong candidate for the mechanosensory element in pilus-mediated surface sensing in C. crescentus . IMPORTANCE Surface sensing allows bacteria to colonize surfaces and form biofilms, with wide-ranging implications for bacterial survival, ecology, and human health. In Caulobacter crescentus , tight adherence (Tad) pili play an important role in surface sensing and attachment, however the molecular mechanisms of pilus-mediated mechanosensing remain unknown. Here, we demonstrate that CpaL, a potential pilus tip mechanosensory protein, could be a major regulatory element controlling Tad pilus-mediated surface attachment and colonization in C. crescentus . Specifically, CpaL plays a regulatory role in holdfast synthesis upon surface contact. By identifying CpaL as a key player in surface recognition, our work offers valuable insights into the mechanisms of bacterial adhesion.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".