Mercury absorption by Pseudomonas fluorescens BM07 grown at two different temperatures

Pseudomonas fluorescens BM07 was characterized as a producer of cold-induced biopolymer by decreasing the temperature down to as low as 10°C. It was previously shown that the synthesis of BM07 biopolymer was inhibited at 30°C. The present study was conducted to investigate the biosorption of mercury (Hg²⁺) ions on the BM07 cells grown on Ml minimal medium at two temperatures (10°C and 30°C). The effects of various factors including pH, contact time, initial concentration of metal and cell biomass on the biosorption yield were also studied. Study of the effect of pH on mercury removal indicated that the metal biosorption increased with increasing pH from 3.0 to 7.0. The optimum adsorption pH value was found to be 7.0. Our results showed that, at optimum pH, BM07 cells were able to uptake the mercury up to 102 and 60 mg Hg²⁺/g dry biomass for 10°C and 30°C grown cells respectively. The removal capacity of cells increased when the cell biomass concentrations increased. The maximum removal efficiency was obtained when cells concentration was 0.83 mg dry biomass/ml for both conditions. The initial metal ion concentration significantly influenced the equilibrium metal uptake and adsorption yield. The equilibrium data were analyzed using Langmuir adsorption model. The qmax was 62.9 and 82.25 mg Hg²⁺/g dry biomass for cells grown at 30°C and 10°C respectively. The results suggest that, the existence of residual cold-induced biopolymer on the external surface of cells may play an important role in biosorption efficiency, as P. fluorescens BM07 cells which were grown at 10°C under similar conditions showed higher efficiency to biosorbe mercury than non-polymer producing cells grown at 30°C.