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

Bioremediation is a rising technique for heavy metal 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 for the optimization of the physiological factors affecting chromium bioremediation 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. the optimum conditions were reached 92.3% chromium removal. The interactions between Cr 6+ concentration (ppm) and inoculum size (ml) were the most significant factors. Electron microscopic and proteomic studies showed that chromium is not adsorbed by the potent consortium but rather bioaccumulated via sulphate transporters with the release of the reduced chromium (Cr 3+ ) in the surrounding medium. Furthermore, consortium B uses malate dehydrogenase and a peptide-binding periplasmic ABC transporter to reduce Cr 6+ to Cr 3+ . It can be concluded that the present consortia is a suitable bioremediation tool.