Repair of DNA damage induced by bile salts in Salmonella enterica

Exposure of Salmonella enterica to sodium cholate, sodium deoxycholate, sodium chenodeoxycholate, sodium glycocholate, sodium taurocholate, or sodium glycochenodeoxycholate induces the SOS response, indicating that the DNA-damaging activity of bile resides in bile salts. Bile increases the frequency of GC --> AT transitions and induces the expression of genes belonging to the OxyR and SoxRS regulons, suggesting that bile salts may cause oxidative DNA damage. S. enterica mutants lacking both exonuclease III (XthA) and endonuclease IV (Nfo) are bile sensitive, indicating that S. enterica requires base excision repair (BER) to overcome DNA damage caused by bile salts. Bile resistance also requires DinB polymerase, suggesting the need of SOS-associated translesion DNA synthesis. Certain recombination functions are also required for bile resistance, and a key factor is the RecBCD enzyme. The extreme bile sensitivity of RecB-, RecC-, and RecA- RecD- mutants provides evidence that bile-induced damage may impair DNA replication.