Replication of the Salmonella Genomic Island 1 (SGI1) triggered by helper IncC conjugative plasmids promotes incompatibility and plasmid loss
Bibliographic record
Abstract
The mobilizable resistance island Salmonella genomic island 1 (SGI1) is specifically mobilized by IncA and IncC conjugative plasmids. SGI1, its variants and IncC plasmids propagate multidrug resistance in pathogenic enterobacteria such as Salmonella enterica serovars and Proteus mirabilis. SGI1 modifies and uses the conjugation apparatus encoded by the helper IncC plasmid, thus enhancing its own propagation. Remarkably, although SGI1 needs a coresident IncC plasmid to excise from the chromosome and transfer to a new host, these elements have been reported to be incompatible. Here, the stability of SGI1 and its helper IncC plasmid, each expressing a different fluorescent reporter protein, was monitored using fluorescence-activated cell sorting (FACS). Without selective pressure, 95% of the cells segregated into two subpopulations containing either SGI1 or the helper plasmid. Furthermore, FACS analysis revealed a high level of SGI1-specific fluorescence in IncC+ cells, suggesting that SGI1 undergoes active replication in the presence of the helper plasmid. SGI1 replication was confirmed by quantitative PCR assays, and extraction and restriction of its plasmid form. Deletion of genes involved in SGI1 excision from the chromosome allowed a stable coexistence of SGI1 with its helper plasmid without selective pressure. In addition, deletion of S003 (rep) or of a downstream putative iteron-based origin of replication, while allowing SGI1 excision, abolished its replication, alleviated the incompatibility with the helper plasmid and enabled its cotransfer to a new host. Like SGI1 excision functions, rep expression was found to be controlled by AcaCD, the master activator of IncC plasmid transfer. Transient SGI1 replication seems to be a key feature of the life cycle of this family of genomic islands. Sequence database analysis revealed that SGI1 variants encode either a replication initiator protein with a RepA_C domain, or an alternative replication protein with N-terminal replicase and primase C terminal 1 domains.
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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".