Fig. 6.

A schematic diagram showing the regulation of catalase gene expression and catalase activity during Zn excess in P. aeruginosa. Zn positively regulates the expression of katA and katB with unclear mechanisms, and simultaneously, Zn activates CzcS/CzcR to negatively regulate the expression of katA and katB through the binding of CzcR at their promoters. As a result, the expression of the key catalase genes katA and katB is not influenced by Zn excess. In spite of the unchanged expression of katA and katB, Zn excess induces catalase activity and H₂O₂ tolerance of P. aeruginosa in a CzcR-dependent manner