High-throughput identification of the impact of ΔrecA mutation on sensitivities to various chemical compounds in Escherichia coli

Antibiotic resistance is currently considered as a global threat to public health. It was shown that adaptive resistance mutation and acquisition of resistance genes by horizontal gene transfer are facilitated by RecA-dependent SOS response during antibiotic treatment. In this study, we performed high-throughput determination of minimal inhibitory concentrations (MICs) of 214 chemicals including not only various kinds of antibiotics but also toxic chemicals of unknown drug action in Escherichia coli wild-type MDS42 strain and the ΔrecA mutant strain. The ΔrecA mutant showed increased sensitivity to DNA-damaging agents, DNA replication inhibitors, and chromate stress. The ΔrecA mutant also showed increased sensitivity to chemicals other than DNA-damaging agents such as S-(2-aminoethyl)- l-cysteine, l-histidine, ruthenium red, D-penicillamine, carbonyl cyanide 3-chlorophenylhydrazone (CCCP), cerulenin, and l-cysteine. Microarray analysis showed that expressions of glnK, nac, and glnLG encoding nitrogen assimilation regulators together with amtB encoding ammonium transporter decreased in the ΔrecA mutant strain. These results suggest that ΔrecA mutation affect not only SOS response but also nitrogen assimilation. Transcriptomes of the ΔrecA mutant strain and the wild-type strain were compared by DNA microarray analysis. Both strains were grown on the modified M9 medium and total RNA was isolated from the cells in the early exponential growth phase. The comparison was performed in triplicate, starting from independent cultures.