264 ISSN 0026-2617, Microbiology, 2017, Vol. 86, No. 2, pp. 264–275. © Pleiades Publishing, Ltd., 2017. Diversity of Bacterial Communities Inhabiting Soil and Groundwater of Arsenic Contaminated Areas in West Bengal, India 1 S. Paul a , Md. N. Ali a, b, *, S. Chakraborty c , and S. Mukherjee a a Department of Agricultural Biotechnology, Faculty Centre for Integrated Rural Development and Management, Ramakrishna Mission Vivekananda University b Department of Agricultural Biotechnology, Faculty of Agriculture, Bidhan Chandra Krishi Viswavidyalaya c Department of Soil Sc. and Agril. Chem, Uttar Banga Krishi Viswavidyalaya *e-mail: nasimali2007@gmail.com Received June 1, 2016 AbstractSoil and water contaminated with arsenic (As) through natural or anthropogenic inputs are com- monly considered as native source of tolerant bacterial strains. The present study was successful in character- izing 12 hyper-tolerant bacteria, satisfying maximum tolerable concentration (MTC) for arsenate (As 5+ ) ≥ 300 mM and arsenite (As 3+ ) ≥ 30 mM, isolated from As affected North 24 Parganas and South 24 Parganas districts of West Bengal, India. Most of the bacteria showing higher level of tolerance to As 5+ and As 3+ were found as gram-positive and bacilli in shape. Positive responses to different biochemical tests indicated that some of these bacteria could be potent sources of various biotechnologically important enzymes. Some of the hyper-tolerant bacteria could reduce As 5+ to As 3+ while all others could oxidise As 3+ to As 5+ . Phylogenetic analysis revealed that those hyper-tolerant bacterial strains were distributed among three phyla such as Acti- nobacteria, Firmicutes, and γ-Proteobacteria. The Firmicutes were well represented in this study with more than half of the hyper-tolerant strains corresponding to members of this group. Moreover, majority of the iso- lates except SR10 belonging to this phylum were affiliated to different species of the genus Bacillus and showed different tolerance capability to As 3+ and As 5+ . We present the first report of the genus Paenibacillus as being involved in arsenite oxidation with hyper-tolerance property to As. Four isolates named as SDe5, SDe12, SDe13, and SDe15 belonging to genera Bacillus and Rhodococcus exhibited highest tolerance to As and therefore represented as good candidates for bioremediation processes of native polluted soil and ground water. Keywords: arsenic, hyper-tolerant bacteria, biochemical characterization, phylogenetic analysis DOI: 10.1134/S0026261717020151 The health status of South-East Asian countries is getting severely affected by soil and groundwater arse- nic (As) contamination since few decades (Mukherjee et al., 2006). Among As-affected countries, India ranks second after Bangladesh (Chakraborti et al., 2009). In recent past, the several areas of India, partic- ularly West Bengal, being As contaminated, received global attention (Chakraborti et al., 2004). Conse- quently, the sufferings from As induced toxicity such as skin lesion (Saha, 1984; GuhaMazumder, 1998; Chakraborti, 2002), lung cancer (GuhaMazumder, 1998), liver cancer (Santra et al., 1999), gastrointesti- nal and cardiovascular diseases (Ahmad et al., 1997; Rahman et al., 1999) etc. have been increased by many folds. This toxic metalloid naturally exists in both organic and inorganic forms with the predominant oxidation states being –3, +3 or +5 (Cullen and Reimer, 1989). Arsenite (As 3+ ) is generally considered as more toxic than arsenate (As 5+ ) due to its relatively higher solubility and mobility (Rhine et al., 2006), higher affinity for protein thiols (Kostal et al., 2004) and inhibition of oxidative phosphorylation (Goyer and Clarkson, 2001). Now a day, in situ or ex situ As remediation using potential microbes, called bioremediation, has gained increased concern in comparison to conventional physico-chemical treatments (Zouboulis and Katsoy- iannis, 2005) due to its ecofriendly and economic approach of management. Bacterial bioremediation became persuasive alternative as bacteria have evolved certain mechanisms either to combat As-induced tox- icity (Bhattacharjee and Rosen, 2007) or even to get benefits from As exposure (Jackson et al., 2003). They utilize As in their metabolism either generating energy through chemoautotrophic As 3+ oxidation (Santini et al., 2000) or using As 5+ as a terminal electron accep- tor in an aerobic respiration (Ahmann et al., 1994). The survival strategies under metal stressed condition 1 The article is published in the original. EXPERIMENTAL ARTICLES