DNA damage induces natural competence.

A. Ciprofloxacin exposure and addA mutation lead to similar transcriptional changes. A comparison of log2 ratios of gene expression changes measured by microarray for ciprofloxacin treatment (2.5 hours, 10× MIC) vs untreated and untreated ΔaddA mutant vs wild-type cells during logarithmic growth. Each condition is represented as mean values measured from multiple microarray experiments from three independent cultures. Regression correlation = 0.9. B. RecA is required for induction of DNA damage responsive genes. Heat map showing 471 genes with 1.6 fold change upon treatment with ciprofloxacin (column 1) or in the ΔaddA mutant (column 2). The enlarged panel shows genes with statistically significant induction in both ciprofloxacin-treated cells and the ΔaddA mutant, as determined by SAM (DNA damage responsive genes), with annotation from strain G27 [46]. Untreated wild-type cells compared to either wild-type cells treated with ciprofloxacin (WT+C), untreated ΔaddA mutant (aA−), untreated ΔrecA mutant (rA−) or the ΔrecA mutant treated with ciprofloxacin (+C). Bottom, scale bar for heat maps in fold change. OMP = outer membrane protein, genes with no annotation are left blank.