Enzyme and Microbial Technology 39 (2006) 883–888 Characterization of an Ochrobactrum intermedium strain STCr-5 manifesting high level Cr(VI) resistance and reduction potential Sikander Sultan 1 , Shahida Hasnain ∗ Department of Microbiology and Molecular Genetics, University of the Punjab, Quaid-e-Azam Campus, Lahore-54590, Pakistan Received 8 July 2005; received in revised form 1 January 2006; accepted 13 January 2006 Abstract The investigation was conducted to evaluate the Cr(VI) resistance and reduction by a bacterial strain STCr-5 under different conditions. Strain STCr-5 tolerated very high concentration of Cr(VI) i.e., >10 mg ml -1 in nutrient broth and up to 8 mg ml -1 in M9 minimal medium. Based on 16S rRNA gene sequence homology, the isolate was identified as Ochrobactrum intermedium. It showed up to 90% reduction with different forms of Cr(VI) (CrO 4 2- , Cr 2 O 7 2- ). O. intermedium STCr-5 exhibited a broad range of Cr(VI) reduction efficiencies at temperatures from 28 to 50 ◦ C and pH levels from 6 to 8. Cr(VI) reduction capability was related to initial cell concentration and Cr(VI) concentration. O. intermedium STCr-5 demonstrated highly efficient Cr(VI) reduction over the Cr(VI) concentration range 100–1000 g ml -1 . Strain STCr-5 reduced 200 g Cr(VI) ml -1 within 72 h and displayed 50% reduction at the highest Cr(VI) concentration of 1000 g ml -1 within 96 h. Cr(VI) reduction ability of strain STCr-5 was not influenced by sulphate and nitrate up to 1000 g ml -1 . The presence of other metals (Cu 2+ , Co 2+ , Mn 2+ , Ni 2+ , Zn 2+ ) significantly stimulated Cr(VI) reduction by this isolate. O. intermedium STCr-5, thus, holds great promise for detoxification of Cr(VI) under a wide range of environmental conditions. © 2006 Elsevier Inc. All rights reserved. Keywords: O. intermedium; Cr(VI) resistance; Cr(VI) reduction; Tannery waste 1. Introduction Disposal of untreated industrial wastes is a major source of environmental pollution in developing countries like Pak- istan. Industrial waste is mainly composed of toxic levels of organic and inorganic compounds including heavy metals such as Cd, Cu, Cr, Zn, Ni, Pb, etc. Bacteria exposed to these met- als in their environment have adapted themselves to this stress by developing various resistance mechanisms such as adsorp- tion, uptake, oxidation, reduction, etc. [1]. Such bacteria could be employed for detoxification/removal of heavy metals from polluted wastewaters [2]. Among the heavy metals, Cr is an important environmental contaminant. It is most extensively used in leather tanning and electroplating [3]. Trivalent (Cr(III)) and hexavalent (Cr(VI)) forms are the dominant oxidation states of Cr in the environ- ∗ Corresponding author. Tel.: +92 42 9231238; fax: +92 42 9230481. E-mail address: genetic@brain.net.pk (S. Hasnain). 1 Present address: Botany Department, Government College Township, Lahore-54770, Pakistan. ment. Cr(VI) is more water soluble and mobile and is a known carcinogen. Cr(III), however, an essential micronutrient, is water insoluble and much less toxic than Cr(VI) [4]. The traditional methods for the treatment of contaminated Cr are expensive as well as energy intensive [5]. Recently bioremediation has emerged as a safe and cost-effective alternative to the expensive routine methods. Many bacterial strains have been reported to reduce the more toxic Cr(VI) to much less toxic Cr(III), indicat- ing an important bioremidial step in detoxification of Cr(VI)- contaminated wastes [1,6–10]. But the availability of effective Cr(VI) reducing bacterial strain is an essential pre-requisite for developing bioremediation process aimed at detoxification of Cr(VI)-contaminated wastewaters. The objective of the present work is thus to characterize the Cr(VI) resistance and reduction potential of such an effective strain STCr-5 isolated from tannery wastes. 2. Materials and methods 2.1. Media Four different media were used in this study: nutrient broth (g l -1 : beef extract, 3; peptone, 5), nutrient agar (g l -1 : beef extract, 3; peptone, 5; bacto-agar, 0141-0229/$ – see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.enzmictec.2006.01.019