Lead and Cadmium Bioremoval by Halomonas sp., an Exopolysaccharide-Producing Halophilic Bacterium

Toxic heavy metals, such as lead (Pb) and cadmium (Cd) are widely used in industry and their accumulation in the living tissues may cause serious health problems and ecological hazards. Twenty four moderately halophilic bacteria isolated from saline environments of Iran were used to study their ability to bioremediation of lead and cadmium. Amongst them, a Gram-negative rod shaped bacterium, designated as strain D showed remarkable ability for removal of Pb and Cd and could grow in media supplemented with 5 mM of these toxic heavy metals. Phenotypic characterization and phylogenetic analysis based on 16S rRNA gene sequence comparisons indicate this strain belongs to the genus Halomonas. Atomic absorption (AA) spectroscopy was used to estimate the removal rate of lead and cadmium by bacterial biomass, autoclaved biomass and exopolysaccharide (EPS) matrix under different conditions. The strain D could uptake more than 90% and 50% of lead and cadmium, respectively. Biomass showed the best lead removal at pH 3.0- 6.0, 35 °C and 5% NaCl (w/v), while the EPS showed maximum removal at pH 5.0, 35 °C and 10% NaCl (w/v). For cadmium removal by biomass, the best results were obtained at pH 3.0, 25 °C and 1% NaCl (w/v) while the EPS showed the optimal cadmium removal at pH 5.0, 45 °C and 1% NaCl (w/v). The results suggest that halophilic bacteria such as Halomonas sp. could be used for remediation of Pb and Cd in contaminated saline soils and wastes discharge sites