Bioreduction of hexavalent chromium by Pseudomonas stutzeri L1 and Acinetobacter baumannii L2

Bioreduction of the very toxic hexavalent chromi- um ion [Cr(VI)] to the non-toxic trivalent chromium ion [Cr(III)] is a key remediation process in chromium- contaminated sites. In this study, we investigated the bioreduction of Cr(VI) by Pseudomonas stutzeri L1 and Acinetobacter baumannii L2. The optimum pH (5–10), tem- perature (27, 37 and 60 °C) and initial chromium Cr(VI) concentration (100–1000 mg L−1) for Cr(VI) reduction by strains L1 and L2 were determined using the diphenylcarbazide method. In the presence of L1 and L2, the bioreduction rate of Cr(VI) was 40–97 and 84–99%, respectively. The bioreduction of Cr(VI) by L2 was higher, reaching up to 84%—than that by L1. The results showed that strain L2 was able to survive even if exposed to 1000 mg L−1 of Cr(VI) and that this tolerance to the effects of Cr(VI) was linked to the activity of soluble enzyme fractions. Overall, A. baumannii L2 would appear to be a potent Cr(VI)-tolerant candidate for the bioremediation of chromium (VI)-contaminated wastewater effluent.