Role of rhizospheric and endophytic bacteria in enhancing plant resistance to soil heavy metal contamination (Review)

This article presents a review of scientific literature published over the past five years in leading Russian and foreign journals concerning heavy metal (HM) contamination in agricultural systems. The use of advanced molecular methods for elucidating interaction mechanisms between plant-associated microorganisms and plants exposed to HM stress is discussed. In addition, the approaches of microbiome engineering and synthetic biology to reducing HM toxicity through HM-resistant strains and using a combination of rhizospheric and endophytic microorganisms are analyzed. The conducted review has revealed that environmentally sustainable biological methods, specifically those involving rhizospheric and endophytic bacteria capable of diminishing HM concentration and toxicity, represent a prominent and rapidly evolving direction in reducing plant HM accumulation. Metal-tolerant microorganisms employ diverse resistance mechanisms, including redox transformations, ion exchange, methylation, complex formation, precipitation, sequestration, and the production of biosurfactants, siderophores, phytohormones, as well as extracellular precipitation and valence alteration. Prior field testing of promising microbial strains is essential for specific crops, cultivars, or rootstocks under defined soil and climatic conditions, due to the variability in potential HM detoxification pathways. The conclusion is made that the use of bacteria which combine plant growth-promoting traits with the ability to detoxify HMs in the rhizosphere or plant endosphere represents a cost-effective and promising approach for eco-friendly agricultural biotechnologies. Optimizing both rhizospheric and endophytic bacterial communities of crops based on microbiome engineering, synthetic biology, and omics technologies appears a prospective and efficient strategy to mitigate the risks of HM contamination in agricultural products.