ABSTRACT
Bacteria, cyanobacteria, algae, fungi and yeasts are able to remove metal ions from their surrounding environment by means of physicochemical mechanisms, as adsorption, and/or metabolic-dependent activity, as transport. When using non-viable biomass, mechanical or chemical treatments after cell growth may increase the maximum metal ion amounts removed by adsorption. Immobilization improves the physical characteristics of biomass for use in reactors, permits continuous operation and protects the microorganisms from microbial degradation. There are six predominant mechanisms by which microorganisms facilitate removal of soluble metal ions from solution: volatilization, extracellular precipitation, extracellular complexing and subsequent accumulation, intracellular accumulation, oxidationreduction reactions and adsorption to the cell surface. The envelopes of cyanobacteria are similar to those of Gram-negative bacteria. The most probable candidates for metal ion binding are the phosphate groups that are resident within the polar head groups of the lipopolysaccharide and phospholipids of the outer membrane, and the carboxylate groups of the peptidoglycan.
