Isolation and characterization of endophytic plant growth-promoting bacteria from date palm tree (Phoenix dactylifera L.) and their potential role in salinity tolerance

Endophytic bacteria were isolated from date palm (Phoenix dactylifera L.) seedling roots, characterized and tested for their ability to help plants grow under saline conditions. Molecular characterization showed that the majority of these strains belonged to the genera Bacillus and Enterobacter and had different degrees of resistance to various antibiotics. Some of these strains were able to produce the enzyme 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and the plant growth regulatory hormone indole-3-acetic acid (IAA). Some strains were also able to chelate ferric iron (Fe3+) and solubilize potassium (K+), phosphorus (PO43-) and zinc (Zn2+), and produce ammonia. The results also showed that ACC deaminase activity and IAA production was slightly increased in some strains in response to an increase in NaCl concentration in the growth media. Consistent with these results, selected strains such as PD-R6 (Paenibacillus xylanexedens) and PD-P6 (Enterobacter cloacae) were able to enhance canola root elongation when grown under normal and saline conditions as demonstrated by a gnotobiotic root elongation assay. These results suggest that the isolated and characterized endophytic bacteria can alter ethylene and IAA levels and also facilitate nutrient uptake in roots and therefore have the potential role to promote the growth and development of date palm trees growing under salinity stress.