Pseudomonas citronellolis strain SLP6 enhances the phytoremediation efficiency of Helianthus annuus in copper contaminated soils under salinity stress

Abstract

Plant growth-promoting bacteria (PGPB)-assisted phytoremediation, is a promising technique for the removal of copper (Cu) from contaminated soils. Moreover, soil salinity is considered to be one of the major threats to plant growth, and may therefore affect the progress and impact of the plant-driven phytoremediation. In this regard, the multiple interactions among Cu-salinity-plant-microbe, remain largely unknown. This study aimed to investigate the potential of PGPB on phytostabilization of Cu contaminated soils using Helianthus annuus growing under salinity stress. A pot experiment was carried out to determine the effects of Cu and salinity tolerant PGPB inoculation in the phytoremediation of Cu-spiked soils by H. annuus under salt-stressed and non-stressed conditions. Cu- and salinity-tolerant bacterial strains were isolated from Cu contaminated soils. Out of the eight bacterial isolates, SLP6 was selected and identified as Pseudomonas citronellolis by 16S rRNA and characterized in terms of its Cu resistance (up to 400 mg L−1), salinity tolerance (up to 8% NaCl, w/v) and plant growth promoting (PGP) traits. Strain SLP6 displayed 1-aminocyclopropane-1-carboxylic acid deaminase activity, indole-3-acetic acid production, siderophores production, and phosphate solubilization under normal, Cu (100–400 mg L−1) and NaCl (2–8%, w/v) stressed conditions. The inoculation of H. annuus seeds with SLP6 strain significantly enhanced the plant growth, chlorophyll content, anti-oxidant enzymes production and Cu accumulation potential under Cu contamination with and without salt stress, whereas they reduced lipid peroxidation. Pseudomonas citronellolis strain SLP6 could be used as a bio-inoculant for improving the phytostabilization of Cu-contaminated saline soils.