Exploration and impact of Metlaoui-Gafsa phosphate rock amendment: the role of Serratia plymuthica BMA1 in phosphate solubilization, heavy metal rhizoaccumulation, and enhanced nutrition in Vicia faba L

The geochemical analysis of Gafsa rock phosphate (GRP) revealed relatively high concentrations of essential plant minerals and trace heavy metals (HMs). Environmental contamination factors indicated moderate to very strong HM contamination due to GRP soil amendment. The potential use of the Serratia plymuthica BMA1 strain, which is known for its ability to solubilize GRP, to enhance mineral nutrition in Vicia faba L. and its role in HM rhizoaccumulation from GRP were explored. Pot experiments revealed that bacterization with S. plymuthica BMA1 in V. faba grown in sand supplemented with GRP as the sole source of phosphorus significantly increased the potassium concentration by 64% in roots and 40% in shoots, iron by 20% in roots and 10% in shoots, and manganese by 27% in roots and 20% in shoots compared to that in V. faba not inoculated with S. plymuthica BMA1. The total dry biomass of V. faba increased by approximately 85%, while the accumulation of cadmium (Cd), copper (Cu), zinc (Zn), and lead (Pb) in the roots increased by 114%, 30%, 37%, and 44%, respectively. However, in the shoots, they increased by 35%, 10%, 85%, and 25%, respectively, for Cd, Cu, Zn, and Pb compared to those in the non-inoculated V. faba. The evaluation of the HM translocation factor, bioaccumulation factor, and bioconcentration factor with GRP highlighted the key role of S. plymuthica BMA1 in preventing the mobility of toxic HMs from reaching the aerial parts of plants. These findings suggest that S. plymuthica BMA1 has the potential to enhance mineral nutrition in V. faba and facilitate the rhizoaccumulation of toxic HMs, which has implications for plant cultivation and human consumption.