Biostimulation effect of Rhodobacter sphaeroides on Arabidopsis thaliana grown in soils contaminated with heavy metals and polychlorinated biphenyls

The study investigated heavy metals (HMs) and polychlorinated biphenyls (PCBs) in a soil from the industrialized area of Taranto, Italy, identifying 16 HMs and 31 PCB congeners. To improve soil quality, plant-assisted bioremediation and beneficial microorganisms were used. The model plant Arabidopsis thaliana was negatively impacted by contamination, but the addition of Rhodobacter (R.) sphaeroides, a growth-promoting photosynthetic bacterium, mitigated its effects. The bacterium overstimulated the expression of the heavy metal-associated proteins, particularly AtHMP23. It also reduced chlorophyll degradation by downregulating the Mg-dechelatase gene, which is otherwise upregulated under pollution stress, showing improved plant health with reduced yellowing of leaves. These findings highlight the potential of R. sphaeroides in supporting plant-assisted bioremediation, making its use a promising strategy for restoring multi-contaminated soils and improving plant resilience to pollutants.