Role of Mfd and GreA in Bacillus subtilis Base Excision Repair-Dependent Stationary-Phase-Mutagenesis

We reported that the absence of a guanine oxidized (GO) system or the AP-endonucleases Nfo, ExoA and Nth promoted stress-associated mutagenesis (SAM) in B. subtilis YB955 (hisC952, metB5, leuc427). Moreover, MutY-promoted SAM was Mfd-dependent suggesting that transcriptional transactions over non-bulky DNA lesions promoted error-prone repair. Here, we inquired whether Mfd and GreA, which control transcription-coupled repair and transcription fidelity, influence the mutagenic events occurring in nutritionally stressed B. subtilis YB955 cells deficient for the guanine oxidized (GO) or the AP-endonuclease repair proteins. To this end, mfd and greA were disabled in genetic backgrounds defective in the GO and the AP-endonuclease repair proteins and tested for growth-associated and SAM. Results revealed that disruption of mfd or greA abrogated the production of SA amino acid revertants in the GO and nfo exoA nth strains, respectively. These results suggest that in nutritionally stressed B. subtilis cells, accumulation of spontaneous non-bulky DNA lesions are processed in an error-prone manner with participation of Mfd and GreA. In support of this notion stationary-phase DeltaytkD DeltamutM DeltamutY (hereafter DeltaGO) and Deltanfo DeltaexoA Deltanth (hereafter DeltaAP) cells accumulated 8-OxoG lesions, which significantly increased following disruption of Mfd. In contrast, during exponential growth, disruption of mfd or greA increased the production of His(+), Met(+) or Leu(+) prototrophs in both DNA repair deficient strains. Thus, in addition to unveiling a role for GreA in mutagenesis, our results suggest that Mfd and GreA promote or prevent mutagenic events driven by spontaneous genetic lesions during the life cycle of B. subtilis ImportanceIn this manuscript, we report that spontaneous genetic lesions of oxidative nature, in growing and nutritionally stressed B. subtilis cells of strain YB955 (hisC952, metB5 and leuC427), drive Mfd- and GreA-dependent repair transactions. However, whereas Mfd and GreA elicit faithful repair events during growth to maintain genome fidelity, under starving conditions, both factors promote error-prone repair to produce genetic diversity allowing B. subtilis to escape from growth-limiting conditions.