Extracellular polysaccharide production by bacteria as a mechanism of toxic heavy metal biosorption and biosequestration in the marine environment

Abstract

Marine environments are one of the most diverse environments owing to their vast natural resource of imperative functional molecules. Interestingly, marine bacteria offer a great diversity of polysaccharides which could play an important role in biotechnology and industry. Among the various bioactive compounds, marine exopolymers are attracting major interest and attention due to their structural and functional diversity. Bacterial exopolysaccharides (EPSs) contain ionizable functional groups, which enable them to bind and sequestrate toxic heavy metal ions. Due to their biodegradability and safety of the environment, biosorption of heavy metals by these biopolymers has attracted considerable attention as promising alternatives capable to compete with expensive, inefficient and conventional technologies, including chemical precipitation, adsorption on activated carbon, membrane separations, ion exchange and solvent extraction methods. This review particularly emphasizes on utilization of marine bacteria in the field of bioremediation and understanding the mechanism behind acquiring the characteristic feature of adaptive responses. Fundamental insights regarding metals in relation to metal-binding proteins/peptides for immobilization, information regarding genetic engineering for enzymes involved in metal transformation and strategies that can be employed to overcome the bottlenecks associated with microbial-based remediation are highlighted in this review. The important engineering properties based on structural characteristics such as adsorption, biodegradability and hydrophilicity/hydrophobicity of EPS matrix are also discussed. A thorough understanding of microbes that produce exopolysaccharides for metal biosequestration and biosorption would solve several problems in bioremediation process.