Transcriptional regulation of two redundant 3-bromo-4-hydroxybenzoate catabolic operons via two different regulatory modes in <i>Pigmentiphaga kullae</i> strain H8

In bacteria, catabolic genes for pollutant degradation often possess functionally redundant duplicates, providing a genetic basis for rapid adaptation to complex polluted environments. Synergic regulation plays an important role in balancing the physiological burden of extra genetic material with the adaptive benefits conferred by genetic redundancy. Although the co-existence of two redundant 3-bromo-4-hydroxybenzoate (3-Br-4-HB)-catabolic operons has been proven to enhance the metabolic robustness and adaptability of the host strain <i>Pigmentiphaga kullae</i> H8, how these two inducible catabolic operons are regulated remains unclear. This study identified two regulators, the LysR-type transcription regulator BhbR1 and the MarR-family transcription factor BhbR2, which activated transcription of the two 3-Br-4-HB-catabolic operons using different modes, and also revealed interactions of these two regulators with their effectors and target promoters. These findings not only clarify two distinct transcriptional strategies employed by redundant catabolic operons but also enhance our understanding of the significance of regulatory diversity for bacterial adaptation to complex polluted environments.