Assessment of Cadmium and Lead effect on the growth of phosphate dissolved bacterium Bacillus polymyxa and its efficiency in vitro

An incubation experiment was conducted to evaluate the effect of heavy metals (cadmium and lead) on growth of phosphate dissolved bacteria (Bacillus polymyxa). Cadmium nitrate and lead acetate were prepared at concentration of 0, 5, 10, 25 and 50 ppm in pvk media. The studies were conducted during different incubation periods 7, 14, 21, 28 and 30 days then estimated the efficiency of the bacteria to dissolve phosphorus fertilizer, adding rock phosphate (10% P) by determining mean of pH level, total acidity and soluble phosphorus in contaminated pvk medium. Results showed that the highest tolerance of B. polymyxa against the metals was found to be at 10 ppm for both cadmium and lead. The parameters affecting the bioadsorption of heavy metals; such as time, metal concentration and biomass concentrations have been investigated, Pb was attained within 14 days as compared with control treatment (no metals) that refers to higher tolerance of bacteria at lag phase and stationary phase than at late phase of growth. Results indicated that B. polymyxa has high ability to solve insoluble phosphorus (rock phosphate) to soluble state, rates (55% and 40%) at 10 ppm for both cadmium and lead respectively as compared to control (concentration = 0), hence efficiency of bacteria improved although contaminated conditions. From this study it is evident the efficiency and biomass are directly related to soluble phosphorus source supply to cells in lag phase than in late phase and live cells absorbed heavy metals more than dead cells.