The Interactive Molecular Mechanism Of Heavy Metals On The Soil-microorganism Interface

Soil microorganisms are the active colloids in the soil, with charges, high specific surface areas and metabolic activities. Many tolerant fungi and bacteria will exist in the soil after polluted by heavy metals, they could influence the species, bioavailability and transportation processes of heavy metals through varies actions. In this paper, a heavy metal-tolerant strain, Pseudomonas putida CZ1, was isolated from the contaminated soils. The actions of biosorption and molecular species of heavy metal binding, the interaction mechanisms of microorganism-clay-metal were investigated using Electron microscopy (EM), Energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and X-ray absorption spectroscopy (XAS) combined with conventional physical-chemical methods, which could provide theory basis for risk evaluation and bioremediation of heavy metal contaminated soils. The main results were as follows:A strain was isolated from the rhizosphere of Elsholtzia splendens obtained from the heavy-metal-contaminated soil in the north-central of Zhejiang province of China. Based on 16S ribosomal DNA sequencing, the microorganism was closely related to Pseudomonas putida. It exhibited high minimal inhibitory concentration (MIC) values (about 3 mM Cu and 5 mM Zn) for metals and antibiotic resistance to ampicillin, but not to kanamycin. Based on the results of heavy metal toxicity screening, inhibitory concentrations in solid media were lower than those in liquid media. Moreover, it was found that the toxicity of copper was higher than that of zinc. Pseudomonas putida CZ1 was capable of removing about 87.2% of Cu and 99.8% of Zn during the active growth cycle with a specific biosorption capacity of 27.7 and 26.0 mg/L, respectively. Although copper and zinc under low concentration slightly damage the surfaces of some cells, it was still demonstrated to have higher biosorption capacities of copper and zinc.It was found that the optimum pH for Zn(II) removal by living and nonliving cells was 5.0, while it was 5.0 and 4.5, respectively for Cu(II) removal. At the optimal conditions, metal ion biosorption was increased as the initial metal concentration increased but the removal efficency decreased. The adsorption data with respect to both metals provide an excellent fit to the Langmuir isotherm. The binding capacity of living cells is significantly higher than that of nonliving cells at tested conditions. It demonstrated that about 40-50%...