This lecture discusses the bioremediation of environments contaminated with transition metals, focusing on the role of microorganisms and plants in reducing metal pollution. Metals are classified according to their biological functions into essential metals required in relatively large amounts, micro-essential metals needed in small quantities, non-essential metals, and toxic metals such as cadmium, lead, and mercury, which can adversely affect human health and biological systems. Metal contamination in water may originate from point or non-point sources and can be managed through conventional methods such as ion exchange, electrolysis, and chemical precipitation. Microorganisms provide an alternative approach through biosorption, in which positively charged metal ions bind to negatively charged functional groups, including phosphate, hydroxyl, carboxyl, and thiol groups, found in microbial cell walls and membranes. Certain microorganisms can also accumulate specific metals, including uranium, mercury, and other transition metals. In contaminated soils, bioremediation can be applied through microbial-assisted phytoremediation, which involves two main processes: phytoextraction and phytostabilization. Phytoextraction uses metal-accumulating plants to absorb and concentrate contaminants from the soil into their tissues, thereby reducing soil metal concentrations, although the harvested plants must not be consumed. Microorganisms support this process by modifying metal oxidation states, producing acids that alter soil pH, and releasing chelating compounds that increase metal availability for plant uptake. The lecture also presents research evidence showing that microbial inoculation can influence cadmium accumulation and distribution between plant roots and shoots. Overall, microbial-assisted bioremediation offers an alternative to costly physical and chemical remediation methods by utilizing microbial activities and plant–microbe interactions to manage transition metal contamination in water and soil.