The protective role of potassium in the adaptation of Pseudomonas protegens SN15-2 to hyperosmotic stress

Pseudomonas protegens is an important biocontrol agent with the ability to suppress plant pathogens and promote plant growth. P. protegens’ ability to endure hyperosmotic stress is crucial to its effectiveness as a biocontrol agent. This study elucidated potassium’s role and mechanism of action in enabling the hyperosmotic tolerance of P. protegens. Potassium was observed to significantly improve the growth of P. protegens under hyperosmotic conditions. Four functionally redundant potassium transporters, KdpA1, KdpA2, TrkH, and Kup, were identified in P. protegens, of which KdpA2 and TrkH were particularly important for its growth under hyperosmotic conditions. Potassium enhanced the biofilm formation and cell membrane stability of P. protegens under hyperosmotic conditions. In addition, we revealed that K⁺ stimulates the expression of several genes related to DNA damage repair in P. protegens under hyperosmotic conditions. Further experiments revealed that the DNA repair-related recG induced by potassium contributes to P. protegens’ hyperosmotic tolerance. We also found that the sigma factor RpoN participates in the hyperosmotic adaptation of P. protegens. Furthermore, we revealed that the opuCABCD operon, whose expression is induced by potassium through RpoN, serves as the key pathway through which betaine, choline, and carnitine improve the hyperosmotic tolerance of P. protegens.