Plant–Microbe Interactions in Bioremediation of Toxic Wastes in Tropical Environment

Abstract

Pollution occurs through natural and anthropogenic activities. Toxic substances generated from different sources may accumulate in the soil and water bodies and potentially alter their physicochemical properties and ecosystem function. Although several environmental remediation methods have traditionally been tried with some success, bioremediation processes have been found eco-friendlier and cost-effective. Plant-assisted bioremediation, a remediation method that utilizes green plants and their associated microflora to eliminate contaminants from the soil or environment has been found commercially applicable because of its cost-effectiveness among other benefits. Phytoextraction, rhizofiltration, phytostabilization, and phytovolatilization among others are techniques commonly used to remove heavy metals and inorganic contaminants from polluted environments. Endophytes such as bacterial or fungal organisms that live within or between healthy plant tissues are known to portray either obligate or facultative association along with complex interaction with their host plant, which may be mutualistic and antagonistic in nature. Plant root exudates also contribute to plant–microbe interaction due to the fact that these exudates provide important nutrients and energy for associated soil microorganisms. Chemotaxis influences the movement of bacteria to plant root by the attraction of root exudates that exist between the soil and the rhizosphere. Specifically, the natural ability of most rhizospheric bacteria to tolerate environmental contaminants has lent them to phytoremediation use, especially in removing organic pollutants from food crops. Similarly, the ability of some plant species to be tolerant to specific stress in a time-dependent manner is being exploited in phytoremediation processes. For example, maintenance of high antioxidant levels that are capable of detoxifying toxic reactive oxygen species is associated with a plant’s ability to tolerate environmental stress. Therefore, information on rhizospheric microorganisms and their benefits in phytoremediation processes should continually be updated, especially in tropical environments where cost is a critical factor. Furthermore, screening of plants to identify those with phytoremediation potentials, especially in tropical regions of the world that harbor rich plant biodiversity is imperative for cost-effective bioremediation of polluted environments.