Journal of Hazardous Materials 165 (2009) 71–77 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Bioprocessing of seleno-oxyanions and tellurite in a novel Bacillus sp. strain STG-83: A solution to removal of toxic oxyanions in presence of nitrate Mohammad Reza Soudi a,∗ , Parisa Tajer Mohammad Ghazvini a , Khosro Khajeh b , Sara Gharavi a a Department of Microbiology, Faculty of Sciences, Alzahra University, Vanak, Tehran, Iran b Department of Biology, Faculty of Sciences, Tarbiat Modares University, Tehran, Iran article info Article history: Received 25 May 2008 Received in revised form 3 September 2008 Accepted 19 September 2008 Available online 26 September 2008 Keywords: Bacillus sp. STG-83 Bioremediation Nitrate Reduction Selenate Selenite Tellurite Volatilization abstract Bioremediation of toxic nonmetal and metalloid oxyanions is of great interest. In this study, among 148 bacterial isolates from two types of polluted water, strain STG-83 showed maximum oxyanion reduction and resistance ability. Sequencing of the 16S rDNA gene of STG-83 showed that the strain is closely related to Bacillus pumilus and morphological and biochemical tests confirmed the result. The strain was nitrate negative, but it could reduce half of tellurite in solution containing 1-mM concentration and completely reduced selenite and selenate in solutions containing 1-mM concentrations. Both reduction to elemental form and volatilization occurred in case of all oxyanions tested, according to hydride generation atomic absorption spectroscopy and proton induced X-ray emission analytical methods. The strain was able to tolerate remarkably high concentrations of selenite (640 mM), selenate (320 mM), and tellurite (1250 M); and tolerance to tellurite increased in presence of selenite and selenate. Biochemical tests and zymogram of extracted culture solutions on gel electrophoresis showed that the strain was nitrate negative and therefore nitrate did not interfere with reduction of other oxyanions. Thus, the strain opens up good opportunities for the bioremediation of polluted waters in natural environment, since nitrate usually inhibits or decelerates reduction of the mentioned toxic oxyanions. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Selenium is found in fossil fuels, shale, alkaline soils and as a constituent in over 40 minerals [1]. Selenate [Se(VI)] and selenite [Se(IV)] are the predominant species in aqueous environments, and occur as soluble oxyanions. Selenium is also found in ground water which may be used as a source of drinking water in many devel- oping countries [2]. Under certain conditions, Se(VI) and Se(IV) can be reduced to insoluble elemental selenium [Se(0)] in natural envi- ronments. Se(0) is the dominant species of Se in anoxic sediments [1], where the transformation of Se in nature occurs primarily by biotic processes [3]. In contrast to selenooxyanions, tellurite [Te(IV)] is generally not found in biological systems. It is more toxic to living organisms than elemental tellurium [Te(0)] and tellurate [Te(VI)], with toxicity being related to its activity as a strong oxidant [4]. Although low Se status is associated with several chronic dis- eases in limited regions [5], the main problem in many areas of the world is assigned to increased concentrations of the related oxyanions in a range of g/mL concentrations which are released in ∗ Corresponding author. Tel.: +98 21 8804 40 51; fax: +98 21 8805 8912. E-mail addresses: msoudi@alzahra.ac.ir, msoudi@yahoo.com (M.R. Soudi). environment due to anthropogenic activities such as mining, fossil fuel combustion, and agricultural activities specially in arid areas. Most of the oxyanionic forms of Se and Te are toxic to living organ- isms and bacteria as well as many other organisms. Microorganisms apply their metabolic capacity in different ways to transform the oxyanions to other non-toxic chemicals, and also possess a high capacity for detoxifying and metabolizing of Se- and Te-oxyanions. In contrast to Se, less work has been carried out on Te inter- actions with microorganisms. Te compounds can be found in considerable concentrations near sites of waste discharge, and their toxicity to living organisms, particularly to gram negative bacteria, is well established [6]. Apparently, microbes that can reduce Se(VI) and Se(IV) are not restricted to any particular group/subgroup of prokaryotes and examples are found throughout the bacterial and archaeal domains [7]. Although microbial reduction of Se(IV) to Se(0) and selenide [Se(II)] has been widely reported [8], reports of Se(VI) being reduced to Se(IV), Se(0), or Se(II) are less numerous [8]. Several bacteria isolated from different environments are capable of reducing Se(VI) to Se(0), These include Wolinella succinigenes, Pseudomonas stutzeri, Bacillus sp. SF-1, Bacillus selenitireducens, Citerobacter freundii, Citerobacter braakii, Enterobactercloacae, Enter- obacter taylorae, Sulfurodpirillum barnesii and Thauera selenatis [9]. Reduction of the mentioned oxyanions is in relation with reduction 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.09.065