Adsorption of chromium by exopolysaccharides extracted from lignolytic phosphate solubilizing bacteria

In the present study, exopolysaccharide (EPS) producing phosphate solubilizing bacterium, Enterobacter soli was screened from rhizospheres soils of mangrove environment. The enhanced production of EPS by Enterobacter soli (EsEPS) was obtained by optimization of cultural conditions, maximum production (3.86 ± 0.03 g/L) was obtained at pH 6.0 and 1% sucrose as carbon source. Biochemical composition of EsEPS was found as 72.83% of carbohydrate and 8.52% of protein. Structural characteristics of EsEPS were investigated using Fourier Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR) and Dynamic Light Scattering (DLS), High Pressure Liquid Chromatography (HPLC) and Matrix-Assisted Laser Desorption/Ionization-Time of Flight (MALDI-TOF). The EsEPS exhibited effective removal of Cr and the highest metal adsorption was found at 6.0 pH. Freundlich and Langmuir isotherm models deployed to determine Cr adsorption ability of EsEPS. Langmuir isotherm fitted well than Freundlich model, maximum adsorption (Qmax) value was 460.82 mg/g. Morphological and structural changes of EsEPS with Cr was characterized using FTIR, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). FTIR results showed changes in wave numbers of functional groups involved in metal adsorption. The SEM micrograph showed changes in surface morphology of EsEPS as the concentration of Cr increased. EDS reports revealed an increasing concentration of Cr involved in the reduction of organic elements of EsEPS. The current study exemplifies the EPS production capacity of E. Soli bacterium and demonstrated effective Cr-removal by EPS through biosorption.