Screening Of Efficient Cadmium-accumulating Strain And Study On Its Accumulation Characteristics

Environmental cadmium pollution is of increasing concern. Microorganisms are deemed to have great potential in treating cadmium pollution. Biosorption, has emerged as the most promising process because of its high efficiency and favorable economics. In this study, microorganisms with high ability of cadmium resistance and accumulation were isolated and screened, then characteristics and mechanisms of cadmium removal by selected strain were studied.One cadmium resistance strain of fungi designated as F2 which could survive 2000mg/L of cadmium was isolated from blende soil with high content of cadmium. It showed high ability of cadmium accumulation. It belongs to Phoma sp. according to morphologic characteristics. When cultured in liquid medium, cadmium with initial concentration below 4.61mg/L didn't inhibited the growth of F2, 163.8mg/L of cadmium affected it obviously but growth continued to a great extent. Cadmium removal from medium by F2 under liquid culture was not so stable with low cadmium concentration below 4.61mg/L, but removal ratio reached 96% with initial cadmium concentration of 163.8mg/L and cadmium content of biomass reached 28%, which showed high capacity of cadmium accumulation by F2. Growth phase of biomass was important for cadmium removal by living biomass of F2, and components of medium seemed interfered in the removal ability. Cadmium adsorption by lyophilized biomass of F2 was more efficient than oven dried biomass with removal ratio above 88% in water with cadmium concentrations of 0.96, 9.22 and 51.3mg/L. The adsorption process accord with stair adsorption kinetics, and initial pH value of solutions has a little effect on cadmium removal.Environmental scanning electron microscopy (ESEM) observation of F2 mycelium cultured in liquid medium with 100mg/L of cadmium showed that there were crystalline precipitations attached to the surface of F2. Transmission electron microscopy (TEM) and energy-dispersive analysis microscope (EDAM) examination revealed that there were many granules with high content of cadmium around the cell wall. Thus precipitations of cadmium outside and inside the cell were considered to be important mechanisms of cadmium resistance and accumulation of F2, and it is possibly related to alkali produced by F2 during growth. These results provide new information on study of mechanisms of cadmium resistance and accumulation in fungi.