Unveiling the performance of a novel alkalizing bacterium Enterobacter sp. LYX-2 in immobilization of available Cd

Abstract

A novel alkalizing strain Enterobacter sp. LYX-2 that could resist 400 mg/L Cd was isolated from Cd-contaminated soil, which immobilized 96.05% Cd2+ from medium. Cd distribution analysis demonstrated that more than half of the Cd2+ was converted into extracellular precipitated Cd through mobilization of the alkali-producing mechanism by the strain LYX-2, achieving the high immobilization efficiency of Cd2+. Biosorption experiments revealed that strain LYX-2 had superior biosorption capacity of 48.28 mg/g for Cd. Pot experiments with Brassica rapa L. were performed with and without strain LYX-2. Compared to control, 15.92% bioavailable Cd was converted to non-bioavailable Cd and Cd content in aboveground vegetables was decreased by 37.10% with addition of strain LYX-2. Available Cd was mainly immobilized through extracellular precipitation, cell-surface biosorption and intracellular accumulation of strain LYX-2, which was investigated through Cd distribution, Scanning Electron Microscope and Energy-Dispersive X-ray Spectroscopy (SEM-EDS), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) analysis. In addition, the application of strain LYX-2 significantly promoted the growth of vegetables about 2.4-fold. Above results indicated that highly Cd-resistant alkalizing strain LYX-2, as a novel microbial passivator, had excellent ability and reuse value to achieve the remediation of Cd-contaminated soil coupled with safe production of vegetables simultaneously.