TABLE 2.

Mechanisms used by some selected PGPB for the enhancement of plant drought tolerance.

PGPB	Notable mechanisms	References
Pseudomonas spp.	Regulation of the pathway involved proline biosynthesis pathway and production of exopolysaccharides (EPS).	Sandhya et al., 2010
P. chlororaphis O6	Production of EPS and production of phytohormones and ACC Deaminase	Vurukonda et al., 2016
A. brasilense and H. seropedicae	Improvement of the water content and cell integrity Improvement of the level of phytohormone production and inducement of the defense-related enzymes and proteins.	Furlan et al., 2017
B. subtilis	Improvement of the relative water content, Production of plant growth regulators, e.g., cytokinin	Liu et al., 2013
B. subtilis RJ46 and Pseudomonas sp. RJ15	Regulation of the level of ethylene Production of ACC deaminases	Saikia et al., 2018
B. pumilu	Increment in enzyme activity such as CAT	Gururani et al., 2013
B. subtilis (LDR2)	Reduction in the content of ACC Increment in the content of IAA Regulation of the rate of optimal transpiration	Barnawal et al., 2017
Bacillus spp.	Increment in the sugar contents Increment in relative water content Decrease in the loss of leaf water	Vardharajula et al., 2011