Chromium bioremediation mechanistic action assessment using bacterial consortium isolated from Egyptian Petroleum Refining Company

Abstract

Bioremediation is a rising technique for heavy metals removal. The current study aimed to evaluate the removal of chromium using a native bacterial consortium. The bacterial consortium B (Providencia rettgri DSM 4542, Bacillus altitudinis 41KF2b and Bacillus tropicus MCCC1A01406) reported the maximum chromium tolerance. Taguchi statistical design was used for the optimization of the physiological factors affecting chromium bioremediation which revealed that 48 h incubation, pH 9; Cr concentration, 90 ppm; inoculum size, 15 ml; inoculum age, 72 h; peptone, 2.5 g; beef extract, 1.5 g; yeast extract, 1.5 g and NaCl, 0.5 g at 40 °C were the optimum conditions reaching 92.3 % chromium removal. The interactions between Cr⁶⁺ concentration (ppm) and inoculum size (ml) were the most significant factors. Electron microscopic and proteomic studies showed that the chromium ions were not adsorbed by the potent consortium but rather bioaccumulated via sulphate transporters with the release of the reduced chromium (Cr³⁺) in the surrounding medium. Furthermore, consortium B used malate dehydrogenase and a peptide-binding periplasmic ABC transporter to reduce Cr⁶⁺ to Cr³⁺. It can be concluded that the present consortia is a suitable bioremediation tool.