Conjugative transfer inhibition of IncA and IncC plasmids by pervasive SGI1-like elements via relaxosome assembly interference
Bibliographic record
Abstract
Broad-host-range IncA and IncC (A/C) conjugative plasmids propagate multidrug resistance in bacteria and mobilize chromosomal resistance islands, including Salmonella Genomic Island 1 (SGI1) across genera. A/C plasmids usually mobilize SGI1 at very high frequencies while being inhibited by SGI1. Here, we identified a broadly conserved fertility inhibitor, which we named CtiC (for 'Conjugative Transfer Inhibition of IncC'), encoded by SGI1 and kin, that hampers A/C plasmid transfer. ctiC expression is both constitutive and activated during conjugative transfer of A/C plasmids. Our results indicate that the suppression of ctiC significantly enhances plasmid transfer, suggesting it counters a general improvement in conjugation mediated by the two genes traHG, located upstream of ctiC in SGI1. CtiC specifically prevents the cotransfer of the helper plasmid, which destabilizes SGI1 in transconjugants. Structural predictions revealed that CtiC resembles the C-terminus of the MOBH12-family relaxase TraI of A/C plasmids. Bacterial two-hybrid assays and relaxase domain substitutions show that CtiC interferes with relaxosome assembly by binding to the plasmid-encoded mobilization factor MobI, which recognizes the origin of transfer, thus preventing its interaction with TraI. Our work reveals a fertility inhibition mechanism that prevents relaxosome assembly and uncovers a functional domain in MOBH12 relaxases.
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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) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 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".