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 Mgdechelatase 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.