Enhanced salinity tolerance in the common bean (Phaseolus vulgaris) plants using twin ACC deaminase producing rhizobacterial inoculation

The present study demonstrates the efficacy of consortium inoculum formulated with two salt-tolerant, 1-Amino-cyclopropane-1-carboxylate (ACC) deaminase producing, Aneurinibacillus aneurinilyticus strain AIOA1 (MH645748) and Paenibacillus sp. strain SG_AIOA2 (MH645749) on common bean plants grown under saline stress (100 mM) conditions. Initially, the common bean seeds were inoculated by coating with bacterial consortium for seedling performance under saline stress conditions. The consortium inoculated common bean seedlings has down-regulated the ethylene levels by similar to 61% and its associated growth inhibition through ACC deaminase activity. It has significantly enhanced seed germination percentage, root/shoot length, fresh weight and dry weight of root/shoot biomass, relative water content (RWC), chlorophyll and carotenoid content as well as osmoprotectants (proline, total soluble sugar) levels of salt exposed common bean plants. Furthermore, consortium application decreased the membrane permeability, electrolyte leakage as well as oxidative stress biomarkers (MDA and H2O2) content of common bean plants. The inoculants scavenged salt-induced reactive oxygen species (ROS) by enhancing the activities of antioxidative defensive enzymes (POD, SOD, CAT) and phenolics content. The strains have the potential to successfully colonize the root surface of plants confirmed by the colony-forming units (CFU) count method as well as bright field and scanning electron microscopy (SEM). The highest occurrence of ACC deaminase producing PGPR was found at root tips of fine roots. We conclude that our two strains are useful bio-inoculants to mitigate the negative impact of salt stress on common bean plants, and these should be field tested to verify their usefulness.