Diversity, metal resistance and uranium sequestration abilities of bacteria from uranium ore deposit in deep earth stratum Ekramul Islam 1 , Pinaki Sar n Department of Biotechnology, Indian Institute of Technology, Kharagpur 721302, India article info Article history: Received 27 August 2015 Received in revised form 31 December 2015 Accepted 4 January 2016 Keywords: Uranium ore deposits Metal resistant bacteria 16S rRNA gene U sequestration Transmission electron microscopy abstract Metal resistance and uranium (U) sequestration abilities of bacteria residing in subsurface U ore was investigated using 122 pure culture strains isolated through enrichment. The cumulative frequencies of isolates resistant to each metal tested were as follows: As(V), 74%; Zn, 58%; Ni, 53%; Cd, 47%; Cr(VI), 41%; Co, 40%; Cu, 20%; and Hg, 4%. 16S rRNA gene analysis revealed that isolated bacteria belonged to 14 genera with abundance of Arthrobacter, Microbacterium, Acinetobacter and Stenotrophomonas. Cobalt did not interfere with the growth of most of the bacterial isolates belonging to different groups while U allowed growth of four different genera of which Stenotrophomonas and Microbacterium showed high U tolerance. Interestingly, tolerance to Ni, Zn, Cu, and Hg was observed only in Microbacterium, Ar- throbacter, Paenibacillus¸ and Acinetobacter, respectively. However, Microbacterium was found to be dominant when isolated from other five different metal enrichments including U. Uranium removal study showed that 84% of the test bacteria could remove more than 50 mg U g À1 dry weight from 80 or 160 mg L À1 U within 48 h. In general, Microbacterium, Arthrobacter and Acinetobacter could remove a higher amount of U. High resolution transmission electron microscopy (HRTEM) study of U exposed cells revealed that accumulated U sequestered mostly around the cell periphery. The study highlights that indigenous U ore deposit bacteria have the potential to interact with U, and thus could be applied for bioremediation of U contaminated sites or wastes. & 2016 Elsevier Inc. All rights reserved. 1. Introduction Groundwater, soil and sediment contamination with U around the world is a persistent threat to the environment and human health for several decades (Sivaswamy et al., 2011; VanEngelen et al., 2011). Excavation and subsequent processing of U ore are one of the major sources contamination of impacted ecosystems. Within the ore deposit U mainly exists as immobile U(IV) form which upon exposure to atmosphere after excavation often transformed into mobile and more toxic form U(VI). Additionally, weathering of U ore bearing rocks and waste rock piles results in the dissemination of toxic metals; thus posing a severe risk of environmental pollution (Anderson and Lovley, 2002; Radeva et al., 2013; Islam et al., 2014; Choudhary and Sar, 2015a; Woods et al., 2015). Understanding the key processes that regulate mo- bility, bioavailability and toxicity of metals including U and other radionuclides present within the ore bodies constitute a critical component for developing sustainable strategies for mining such minerals (Kenarova et al., 2014; Newsome et al., 2014; Woods et al., 2015). It is observed that inhabitant bacteria within heavy metal (HM) and radionuclide rich natural deposits are well adapted to the ‘local harsh conditions’ and play critical role in biogeochemical cycling of toxic elements including their mobility and toxicity (Suzuki and Banfield, 2004; Choudhary and Sar, 2015b). Interac- tion of the indigenous bacteria with these metallic elements often leads to their precipitation and immobilization that are being considered as one of the promising remediation strategies for cleaning up contaminated environments (Kazy et al., 2009; Lloyd and Macaskie, 2000). Considering the abundance and diversity of bacteria in natural U and other HM rich environments with su- perior metal resistance and removal capacities it is considered to be of great importance to identify the metal resistant populations and characterize their metal removal/sequestration potential. In the past, several studies aimed to decipher microbial community composition and function in U rich environment including both anthropogenic and natural U containing sites (Geissler, 2007; Is- lam and Sar, 2011a, Islam et al., 2011; Radeva et al., 2013; News- ome et al., 2014; Islam et al., 2014 and references within). Al- though a number of these reports provided information on Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ecoenv Ecotoxicology and Environmental Safety http://dx.doi.org/10.1016/j.ecoenv.2016.01.001 0147-6513/& 2016 Elsevier Inc. All rights reserved. n Corresponding author. E-mail addresses: ekramul.rs@gmail.com (E. Islam), sarpinaki@yahoo.com (P. Sar). 1 Present address: Department of Microbiology, University of Kalyani, Kalyani 741235, India. Ecotoxicology and Environmental Safety 127 (2016) 12–21