Bacillus flexus strain As-12, a new arsenic transformer bacterium isolated from contaminated water resources Mohammad Ahmadi Jebeli a , Afshin Maleki a, *, 1 , Mohammad Ali Amoozegar b, c , Enayatollah Kalantar d, **, 1 , Hassan Izanloo e , Fardin Gharibi a a Environmental Health Research Center, Kurdistan University of Medical Sciences, Sanandaj, Iran b Extremophiles Laboratory, Department of Microbiology, Faculty of Biology University of Tehran, Tehran, Iran c Center of Excellence in Phylogeny of Living Organisms, College of Science, University of Tehran, Tehran, Iran d Dietary Supplement and Probiotic Research Center, Alborz University of Medical Sciences, Karaj, Iran e Research Center for Environmental Pollutants, School of Public Health, Qom University of Medical Sciences, Qom, Iran highlights graphical abstract  Isolation of arsenic-resistant bacteria from arsenic-contaminated traver- tine spring water.  Identification of a new Gram-stain- positive, endospore-forming rod- shaped, non-motile with high resis- tance to arsenate.  Exploration and recognition of Bacil- lus flexus strain As-12 as a new arsenic transformer bacterium.  Bacillus flexus strain As-12 was an arsenic transformer and can used for in-situ bioremediation. article info Article history: Received 26 May 2016 Received in revised form 24 November 2016 Accepted 25 November 2016 Handling Editor: T Cutright Keywords: Arsenic Bioremediation Bacillus flexus Water resource abstract A total of 14 arsenic-resistant bacteria were isolated from an arsenic-contaminated travertine spring water in the central district of Qorveh county, Kurdistan Province, Iran. One of strains designated As-12 was selected for further investigation because of its ability to transform arsenic. The strain was identified by cultural, morphological and biochemical tests, and 16S rRNA gene sequencing. Finally, the growth characteristics of the isolate were investigated in a chemically defined medium which included varied ranges of environmental factors such as pH, temperature and salinity. Moreover, the resistance of this strain to some heavy metals was evaluated. The bacterium was a Gram-positive, endospore-forming with all other characteristics of the genus Bacillus. It revealed maximum similarity at the 16S rRNA gene level with Bacillus flexus. The optimum growth of the strain was observed at 38  C, pH 9 and 2% salinity. This strain was resistant to heavy metals such as zinc, chromium, lead, nickel, copper, mercuric and cadmium at concentrations of 15 mM, 15.5 mM, 11.5 mM, 12 mM, 11 mM, 5.5 mM, and 1 mM, respectively. The isolated bacterium was able to reduce As (V) to As (III) (about 28%) and oxidize As (III) to As (V) (about 45%) after 48 h of incubation at 37  C. In conclusion, Bacillus flexus strain As-12, was identified as an arsenic transformer, for the first time. © 2016 Elsevier Ltd. All rights reserved. * Corresponding author. ** Corresponding author. E-mail addresses: maleki43@yahoo.com (A. Maleki), ekalantar@hotmail.com (E. Kalantar). 1 These two authors have equal roles in this study. Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere http://dx.doi.org/10.1016/j.chemosphere.2016.11.129 0045-6535/© 2016 Elsevier Ltd. All rights reserved. Chemosphere 169 (2017) 636e641