Alginate overproduction in Pseudomonas aeruginosa can be caused by the proteolysis of the anti-sigma factor MucA regulated by the AlgW protease. Here, we show that inactivation of MucD, an HtrA/DegP homolog and alginate regulator, can bypass AlgW, leading to an atypical proteolysis of MucA that is dependent on the MucP protease.