Evaluation of the Phytoprotective and Plant Growth-Promoting Role of Pseudomonas agronomica in the Forage Crop Lupinus albus var. Dorado Grown in Mercury-Contaminated Soils

Abstract

Soil contamination by mercury (Hg) represents a significant ecotoxicological risk due to its high toxicity and environmental persistence. This study evaluated the effects of the native strain Pseudomonas agronomica on the growth, physiological status and antioxidant response of Lupinus albus cultivated in soils with different Hg concentrations, as well as the influence of inoculation on Hg accumulation and translocation within plant tissues. A pot experiment was conducted using three Hg levels, with and without bacterial inoculation. Plant growth and antioxidant parameters were assessed, Hg concentrations were quantified by ICP-MS, and soil metabolic activity and microbial community structure were analyzed using Biolog EcoPlates®, cenoantibiogram assays and 16S rRNA gene sequencing. Inoculation with P. agronomica significantly reduced Hg accumulation in roots and leaves (p < 0.001) and malondialdehyde levels (p < 0.05), decreased community-level antibiotic resistance, and increased plant biomass, particularly at intermediate Hg concentrations, while enhancing soil functional diversity without altering alpha diversity. Overall, these findings highlight the potential of Pseudomonas agronomica C69 as a native plant growth-promoting bioinoculant to improve the sustainable cultivation and phytoremediation capacity of low-alkaloid Lupinus albus grown in Hg-contaminated soils.