Bacillus strains exhibit various plant growth promoting traits and their biofilm-forming capability correlates to their salt stress alleviation effect on maize seedlings.

Soil salinity interferes with plant growth and development. Bacillus genus has been used to increase the growth and productivity of a wide variety of crops by alleviating the effects of salt stress. A total of thirty two Bacillus isolates were obtained from maize rhizosphere, and their plant growth-promoting (PGP) traits and biocontrol activities were tested. Bacillus isolates displayed varying degrees of PGP properties-the production of extracellular enzymes, indole acetic acid, hydrogen cyanide, phosphate solubilization, biofilm formation, and antifungal potential against several fungal pathogens. The phosphate-solubilizing isolates belong to B. safensis, B. thuringiensis, B. cereus, and B. megaterium species. Each Bacillus isolate demonstrated different levels of antifungal activity against the fungal pathogens tested. Biofilm production by some salt-tolerant isolates significantly increased at elevated levels of NaCl (p < 0.05). The strains B. safensis B24, B. halotolerans B7/B18, B. subtilis B26, and B. thuringiensis B10 significantly increased the length of root (by 32.7-38.2%) and shoot (by 19.5-29.8%) of maize (p < 0.05). Maize plants treated with some Bacillus strains displayed significantly greater chlorophyll content with an increase of 26.7-32.1% (p < 0.05). Among PGP properties, enhanced biofilm formation played a more important role in maize growth under higher salinity. These salt-tolerant biofilm-forming strains could be efficiently used as bio-inoculant for maize under salinity stress.