SOS Genes Are Rapidly Induced While Mutagenesis Is Temporally Regulated by Changes in Protein Activation and Nucleotide Pools After a Sub-lethal Dose of Ciprofloxacin in Escherichia coli

The DNA damage inducible SOS response in bacteria serves to increase survival of the species. The SOS response first initiates error-free repair which is followed by error-prone repair. Here, we have employed a multi-omics approach to elucidate the temporal coordination of the SOS response using transcriptomics, signalomics, and metabolomics. Escherichia coli was grown in batch cultivation in bioreactors to ensure highly controlled conditions, and a low dose of ciprofloxacin was used to activate the SOS response while avoiding extensive cell death. Our results show that expression of genes involved in error-free and error-prone repair were both induced shortly after DNA damage, thus, challenging the established perception that the expression of error-prone repair genes is delayed. By combining transcriptomics with signalomics, we found that temporal segregation of error-free and error-prone repair is primarily regulated after transcription. Furthermore, the heterology index was correlated to the maximum increase in gene expression and not to the time of induction of SOS genes. Finally, quantification of metabolites revealed increasing pyrimidine pools as a late feature of the SOS response. Our results elucidate how the SOS response is coordinated, showing a rapid transcriptional response and temporal regulation of mutagenesis on the protein and metabolite levels.