FleQ-Dependent regulation of the ribonucleotide reductase repressor NrdR in Pseudomonas aeruginosa during biofilm growth and infection.

Ribonucleotide reductases (RNRs) are essential enzymes that catalyze the conversion of ribonucleotides to deoxyribonucleotides (dNTPs), a critical step in DNA synthesis and repair. While all organisms encode for at least one RNR class, Pseudomonas aeruginosa harbors three, providing a competitive advantage that allows it to adapt and colonize various environments. Despite their importance, the mechanisms coordinating the expression of different RNRs in microorganisms with multiple RNR classes remain poorly understood. The transcriptional regulator NrdR controls the expression of all three RNR classes by binding to conserved motifs (NrdR boxes) in their promoters. However, the regulation of nrdR itself remains unknown. In this study, we investigated the transcriptional regulation of nrdR using a combination of bioinformatics and experimental approaches we identified potential transcription factors (TF) involved in nrdR regulation. Our analysis identified four potential TF that could regulate nrdR, and we experimentally confirmed that specifically, FleQ is responsible for regulating nrdR expression under aerobic and anaerobic conditions. Furthermore, we explored nrdR regulation under biofilm-forming conditions and in the Galleria mellonella infection model to gain insights into how nrdR might be regulated in vivo.