SOS Response
One-Sentence Definition
The SOS response is a global DNA-damage stress program in bacteria, controlled by LexA and RecA, that induces repair functions, error-prone polymerases, and sometimes prophage excision or competence — accelerating mutation and evolution under antibiotic stress.
Simple Explanation
When bacterial DNA is badly damaged, the cell flips an emergency switch: repair what you can, mutate faster if you must, and sometimes wake sleeping phages.
Detailed Scientific Explanation
| Player | Role |
|---|---|
| LexA | Transcriptional repressor of SOS genes |
| RecA* | Activated by ssDNA; co-protease triggering LexA autocleavage |
| Error-prone Pols (e.g. UmuDC / Pol V) | Translesion synthesis → mutations |
| SulA etc. | Cell division delay |
Triggers: UV, some antimicrobials (fluoroquinolones, trimethoprim, β-lactams via secondary effects), oxidative stress. Links to Persisters and Antibiotic Tolerance, Prophage Detection and Annotation (SOS-induced phage), and Bacterial Competence Systems in some species.
Mechanism
DNA damage → RecA nucleoprotein filaments → LexA cleavage → derepression of SOS regulon → repair + mutagenesis → possible return to repression after recovery.
Clinical Importance
- Sublethal bactericidal stress can raise mutation supply → faster resistance emergence (Mutation and Selection).
- Explains mutagenesis under fluoroquinolone pressure beyond target mutations alone.
Research Importance
- Anti-evolution strategies (LexA/RecA inhibitors) aim to slow AMR.
- Systems biology of stress–mutation coupling.
Diagnostic Relevance
- Indirect: hypermutator phenotypes (MMR defects) overlap clinically with chronic infections (P. aeruginosa in CF).
AMR Relevance
High evolutionary relevance — SOS is a highway from susceptible populations to resistant clones under therapy.
Related Methods
- Microbial Transcriptomics · fluctuation tests · WGS of serial isolates
Related MOCs
Learning Aids
Clinical Example
Example
Case: E. coli UTI treated with ciprofloxacin; follow-up isolate acquires gyrA mutation.
Question: Besides simple selection, what stress program may have increased mutation rate?
Answer: SOS response induced by quinolone DNA damage — error-prone polymerases raise the chance of target-site mutations.
Active Recall Questions
- What do RecA and LexA each do in SOS?
- How can SOS accelerate AMR evolution?
- Name one antibiotic class classically linked to SOS induction.