(88e) Exploring the Interlinks between SOS Response, Mutagenesis, and Resistance during the Recovery Period

Although the mechanistic connections between SOS-induced mutagenesis and antibiotic resistance are well-established, our current understanding of the impact of SOS response levels, recovery durations, and transcription/translation activities on mutagenesis remains relatively limited. In this study, when bacterial cells were exposed to mutagens like ultraviolet light for defined time intervals, a compelling connection between the rate of mutagenesis and the RecA-mediated SOS response levels became evident. Our observations also indicate that mutagenesis primarily occurs during the subsequent recovery phase following the removal of the mutagenic agent. When transcription/translation was inhibited or energy molecules were depleted at the onset of treatment or during the early recovery phase, there was a noticeable decrease in SOS response activation and mutagenesis. However, targeting these processes later in the recovery phase does not have the same effect in reducing mutagenesis, suggesting that the timing of inhibiting transcription/translation or depleting energy molecules is crucial for their efficacy in reducing mutagenesis. Active transcription, translation, and energy availability within the framework of SOS response and DNA repair mechanisms appear to be conserved attributes, supported by their consistent manifestation across diverse conditions, including the use of distinct mutagens such as fluoroquinolone antibiotics and various bacterial strains.

Furthermore, we implemented a two-step screening methodology to gain a deeper understanding of the downstream mechanisms of RecA-mediated mutagenesis. In the first method, we screened RecA-LexA-regulated promoters by exposing cells carrying the promoter reporters to UV, aiming to identify SOS response genes significantly upregulated upon UV exposure (Fig.1). In the second method, we screened an E. coli knockout cell library encompassing all potential repair mechanisms that might be involved in the observed mutagenesis, particularly focusing on genes whose expression was not significantly upregulated in our initial screening. Through these methods, we identified several genes whose deletions significantly affected either mutagenesis alone (e.g., umuC and umuD) or both mutagenesis and cell culturability (e.g., uvrA and recB) (Fig.1). Monitoring the expression level of the candidate genes using flow cytometry provided a deeper insight into their regulation and potential roles in UV-induced mutagenesis and cell culturability. Overall, this study sheds light on the complex interplay among the convoluted, error-prone mutagenic pathways in the context of antibiotic resistance and evolutionary processes.