Genetic and biochemical determinants in potentially toxic metals resistance and plant growth promotion in Rhizobium sp LBMP-C04

The association of bacteria resistant to potentially toxic metals (PTMs) with plants to remove, transfer, or stabilize these elements from the soil is an appropriate tool for phytoremediation processes in metal-contaminated environments. The objective of this study was to evaluate the potential of Rhizobium sp. LBMP-C04 for phytoremediation processes and plant growth promotion in metal-contaminated soils. Functional annotation allowed us to predict a variety of genes related to PTMs resistance and plant growth promotion in the bacterial genome. Resistance genes are mainly associated with DNA repair, and the import or export of metals in bacterial cells to maintain cell homeostasis. Genes that promote plant growth are related to mechanisms of osmotic stress tolerance, phosphate solubilization, nitrogen metabolism, biological nitrogen fixation, biofilm formation, heat shock responses, indole-3-acetic acid (IAA) biosynthesis, tryptophan, and organic acids metabolism. Biochemical tests indicated that Rhizobium sp. LBMP-C04 can solubilize calcium phosphate and produce siderophores and IAA in vitro in the presence of the PTMs Cd²⁺,Cu²⁺,Cr³⁺,Cr⁶⁺, Zn²⁺, and Ni²⁺. Results indicate the possibility of using Rhizobium sp. LBMP-C04 as a potentially efficient bacterium in phytoremediation processesin environments contaminated by PTMs and simultaneously promote plant growth.