Mechanisms of Hexavalent Chromium Reduction by Rhodococcus qingshengii strain SC26

Chromium represents a serious threat for both human health and ecosystems equilibrium. It is mainly present in two stable inorganic forms: trivalent and hexavalent, the latter one being more toxic due to its high solubility and mobility in biological systems. The major pollution sources are electroplating and tannery industries. Among possible remediation strategies, the use of biological systems can be proposed since microorganisms interact with metals by passive adsorption processes and active enzymatic reactions. In the present study, Rhodococcus quingshengii strain SC26 was characterized for its ability to resist to hexavalent chromium (MIC of 300 mg L-1) and to reduce up to 51.14 mg L-1 hexavalent to trivalent chromium in growing-cell conditions. The reduction was always paralleled by cell growth. Part of the metal was present on cell pellet (1.9 mg g-1). Not proliferating cells were not able to reduce/adsorb hexavalent chromium, thus excluding passive adsorption processes. Trials conducted with contaminated electroplating wastewaters are ongoing to assess the bioremediation potential of R. qingshengii strain SC26 in close-to-real scenarios.