Choline-betaine pathway contributes to hyperosmotic stress and subsequent lethal stress resistance in Pseudomonas protegens SN15-2

ABSTRACT

Pseudomonas protegens SN15-2, a typical non-spore-forming rhizosphere bacterium, has excellent biocontrolcapabilities; thus, it is necessary to explore the stress resistance of SN15-2. The choline–glycine betainepathway is considered as an important mechanism by which bacteria adapt to stressful environments. In thiswork, we demonstrated that the expression of the betA and betB genes, which are involved in the choline–glycine betaine pathway in SN15-2, was highly increased by 12-fold and 26-fold, respectively, by hyperosmotic stress and choline treatment. The accumulation of betaine in SN15-2 (5.54 g/L) was significantly higherthan that in the mutants D betA (3.44 g/L) and D betB (2.68 g/L) under hyperosmotic stress and cholinetreatment. Moreover, choline enhanced the growth of SN15-2 greatly, but it did not enhance the growth of DbetB under hyperosmotic stress. Choline combined with hyperosmotic adaptation significantly increased thelethal stress resistance of SN15-2 while the resistance of D betA and D betB was significantly decreased. Thisresearch illuminated a strategy underlying the adaptation to osmotic stress in P. protegens and provided aneffective method to improve the stress resistance of this species, thus provided a theoretical basis for thepractical application of P. protegens SN15-2.