Molecular identification and characterization of phytobeneficial osmotolerant endophytic bacteria inhabiting root nodules of the Saharan tree Vachellia tortilis subsp. raddiana.

Nodular endophytes of drought-tolerant legumes are understudied. For this reason, we have isolated and studied non-symbiotic endophytic bacteria from nodules of Vachellia tortilis subsp. raddiana, a leguminous tree adapted to the harsh arid climate of Southern Morocco. Rep-PCR analysis followed by 16S rDNA sequencing revealed two main genera, Pseudomonas and Bacillus. Isolates responded variably to salt and water stresses, and mostly produced exopolysaccharides. Differences concerned also plant growth-promoting activities: phosphate, potassium, and zinc solubilization; biological nitrogen fixation; auxin, siderophore, ammonia, and HCN production; and ACC deaminase activity. Some strains exhibited antagonistic activities against phytopathogenic fungi (Fusarium oxysporum and Botrytis cinerea) and showed at least two enzymatic activities (cellulase, protease, chitinase). Four selected strains inoculated to vachellia plants under controlled conditions have shown significant positive impacts on plant growth parameters. These strains are promising bio-inoculants for vachellia plants to be used in reforestation programs in arid areas increasingly threatened by desertification.