Molecular identification of rhizobacterial isolates from Prosopis limensis and their effect on the growth of Raphanus sativus under salt stress

Abstract

Soil salinity negatively affects the development of agricultural crops. The utilization of plant growth-promoting rhizobacteria is a biotechnological alternative to mitigate this problem. Rhizobacteria were isolated from the roots and rhizosphere of Prosopis limensis Bentham "carob" to identify them and determine their potential as plant growth-promoters under salt stress. First, ACC deaminase activity was determined in Dworkin & Foster (DF) minimum medium with 3.0 mM ACC as a source of nitrogen; besides, tolerance to sodium chloride was determined in Nutrient Broth (NB) supplemented with 10% NaCI. Then, bacteria displaying ACC deaminase activity and a 10% NaCI tolerance were selected, identified through genomic analysis targeting the 16s rRNA gene, and inoculated into Raphanus sativus L. "radish" seeds to determine the effect on germination percentage under salt stress (80 mM NaCI) and, also on indole production and phosphate solubilization. Isolates were also utilized to evaluate their effect on the growth of radish in saline soils. Genomic analysis showed two bacterial isolates from the genus Pseudomonas and one from the genus Bordetella: Isolate MW604823 was identified as Pseudomonas sp.; isolate MW604824, as Pseudomonas hunanensis; and isolate MW604826 as Bordetella muralis. Thee isolates demonstrated ACC deaminase activity and tolerance to 10% NaCI. Inoculation of the isolates on radish seeds increased germination percentage compared to the control. The isolates displayed in vitro indole production and phosphate solubilization capacity. Moreover, the isolates promoted the growth of radish under salt stress conditions, increasing, leave number, root number, aerial, and root biomass, demonstrating their potential as a biofertilizers.