Strategies for cadmium remediation in nature and their manipulation by molecular techniques: a comprehensive review

The entire environmental integrity is intrinsically tied to the quality of life on earth. The protection of freshwater resources for present and future use is one of the significant global issues. Industrialization introduces toxic metals such as Cadmium, Lead, Mercury, Arsenic, Copper, etc. and their derivatives in the environment which are mutagenic and cancerous even at low doses. Cadmium (Cd) is categorized as a group 1 human carcinogen. Considering its possible removal from the environment, different strategies are used to lessen its concentration in the ecosystem. The conventional techniques used to remove heavy metals have some limitations. Given the restrictions of traditional approaches, the requirements for innovative technologies becomes evident. This narrative review is focused on the following three key aspects. How gene modifications in microorganisms enhance their biodegradation capabilities with the help of overexpression of different metal binding proteins in microbes, such as phytochelatins, glutathione, metallothioneins, CrMTP4, pyrroline-5-carboxylate synthetase and histidine oligopeptide, for the removal of contaminants, specifically Cd. Use of agricultural waste for phytoremediation: The description of genetically and chemically modified wastes from agriculture such as husks, sugarcane bagasse, wheat bran, pineapple waste, date pit, pomegranate and orange peel and different modified strategies for Cd removal, is also provided. Nanotechnology in microbial cell immobilization: The achievements of different strategies especially immobilization and its advantages over free cells. This review discusses the advantages of immobilization of genetically engineered microorganisms are a favored innovation for harnessing the extraordinary metabolic pathway characteristics of microorganisms and nanomaterials enhancement of efficiency and stability of such cells.