The effect of salinity-resistant biofilm-forming Azotobacter spp. on salt tolerance in maize growth

Abstract

Increasing soil salinity is among the most detrimental threats restricting crop growth and productivity. In recent years, root inoculation with biofilm-forming plant growth-promoting rhizobacteria (PGPR) has been greatly interested in improving abiotic stress tolerance. This study examined the plant growth-promoting and biofilmforming potential of Azotobacter spp. obtained from maize rhizosphere, tested the salinity effect (up to 300 mM NaCl) on biofilm formation and exopolysaccharide (EPS) production, and evaluated their effect on maize growth at different concentrations (0, 50, and 150 mM) of NaCl under greenhouse conditions. The isolates produced different amounts of indole acetic acid (IAA) (from 0.96 to 7.51 µg mL −1 ) and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (from 2.10 to 19.50 µmol α-ketobutyrate mg −1 h −1 ). On average, the highest biofilm formation was found in A. chroococcum. Both biofilm formation and EPS production significantly increased (p < 0.05) at 150 and 300 mM NaCl in A. chroococcum SC8, A. beijerinckii SC10, and A. tropicalis SC4. These strains also significantly increased (p < 0.05) root depth by 44.1-55.9%, shoot height by 52.3-58.8%, fresh root weight by 42.8-52.4%, and fresh shoot weight by 44.6-53.6% at 150 mM NaCl compared with the uninoculated salinitystressed (control) treatment. Among plant growth regulators, higher biofilm formation and EPS production under increasing salinity exhibited better maize growth under salinity stress. Therefore, these respective strains might be promising bioinoculants for alleviating salinity stress in field experiments.

Metal-Resistant PGPR Strain Azospirillum brasilense EMCC1454 Enhances Growth and Chromium Stress Tolerance of Chickpea (Cicer arietinum L.) by Modulating Redox Potential, Osmolytes, Antioxidants, and Stress-Related Gene Expression

“…Recent reports demonstrated significant consequences of environmental stresses (salinity and heavy metals) on the stress-tolerant traits of PGPR, such as survivability, biofilms, ACC deaminase activity, minerals uptake, and generation of exopolysaccharide and IAA [34,42,77]. In the current study, the bacterial population in culture media amended with 0, 130, and 260 µM K 2 Cr 2 O 7 was measured to determine the survivability of A. brasilense EMCC1454.…”

“…and IAA [34,42,77]. In the current study, the bacterial population in culture media amended with 0, 130, and 260 µM K2Cr2O7 was measured to determine the survivability of A. brasilense EMCC1454.…”

“…The highest levels of trehalose (3.4 µ/mg FW), ACC deaminase (0.68 µmol α-ketobutyrate mg −1 h −1 ), IAA (41.9 µg mL −1 ), and exopolysaccharides (6.3 mg mL −1 ) were recorded at 260 µM K2Cr2O7 (Figures 3B and 4). and IAA [34,42,77]. In the current study, the bacterial population in culture media amended with 0, 130, and 260 µM K2Cr2O7 was measured to determine the survivability of A. brasilense EMCC1454.…”