Role of bacterial extracellular polymeric substances (EPS) in uptake and accumulation of co-contaminants

Coexistence of many contaminants in effluents discharged from industries is a serious environmental concern, even though these contaminants can individually be transformed into less toxic forms, but very few studies have reported simultaneous treatment of such contaminants. Present work was aimed at investigating the capability of extracellular polymeric substances from Bacillus subtilis MB378 for simultaneous uptake and accumulation of malachite green dye and selected metals (Cr, Cu and Cd). EPS showed highest uptake of cadmium (95.31%) at a rate of 1.04 mg g−1 without any dye addition. Chromium removal efficiency of 91.12% combined with malachite green was observed with a unit adsorption rate of 0.54 mg g−1, while 90.98% of copper removal was recorded in the presence of malachite green dye with highest binding capacity of 1.84 mg g−1 compared to individual metal ions. However, a reduction in color removal efficiency was noticed for malachite green in combination with metals compared to dye molecules alone. Quantification of decolorization revealed 94.91% removal of dye molecules by bacterial cells with EPS following bacterial cells without EPS (87.02%) and EPS (82.34%). Highest dye binding affinities of 0.66 and 0.64 mg g−1 were observed on combining the dye with chromium and cadmium, respectively. The formation of new peaks, disappearance and shifting of exiting in the UV–Vis absorption and FTIR spectra suggested possible adsorption and accumulation of dye combined with metals onto the charged or ionizable functional groups present on EPS surface, indicating EPS from B. subtilis MB378 as promising adsorbent in terms of potential pollutant removal and remediation.