Application of Plant Endophytic Microorganisms (Endophytes) in the Treatment of Heavy Metal Pollution in Soils

Heavy metal contaminated soils may pose risk and hazards to humans and the ecosystem. Physiochemical approaches have been widely used for remedying polluted soil; however, their large-scale application is difficult due to high cost and side effects. Current research interests are moving towards the application of in situ strategies to reduce costs and to resolve pollution dispersal problems. Phytoremediation is a plant-based, environment-friendly, and cost-effective technology that can potentially be used to remediate contaminated media. However, phytoremediation is with some critical shortcomings, such as phytotoxicity, slower than mechanical method and limited mechanical uptake. Some plant-associated bacteria can overcome these constraints by assisting plants to accumulate higher amount of metal without increasing phytotoxity. While rhizosphere microorganisms can enhance phytoremediation according to numerous studies, endophytes appear to do so more efficiently by interacting closely with host plants. Endophytes are all microorganisms that inhabit the interior of plant tissues, causing no harm to the host and developing no external structures. In the plant endophyte symbiosis, endophytes receive carbohydrates from plants and improve plant resistant to biotic and abiotic stresses in return. Moreover, recent studies showed that many endophytes are metal resistant, able to degrade organic contaminants and have been successfully used in phytoremediation. This paper focuses on the overview of studies on the ability of endophytes to support plant absorption of heavy metals as an object with potential in environmentally friendly and inexpensive bioremediation.