Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech Isolation and characterization of biosurfactant producing and oil degrading Bacillus subtilis MG495086 from formation water of Assam oil reservoir and its suitability for enhanced oil recovery Poulami Datta a , Pankaj Tiwari a,b, ⁎ , Lalit M. Pandey a,c, ⁎ a Centre for the Environment, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India b Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India c Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India ARTICLE INFO Keywords: Isolation Biosurfactant Crude oil Surface tension Optimization ABSTRACT The strains isolated from the formation water were characterized and screened considering their crude oil de- gradation capability and biosurfactant production ability. The growth kinetics study of isolated Bacillus subtilis MG495086 was carried out by varying growth parameters i.e. carbon source, temperature, pH and salinity. The biosurfactant production was optimized adopting RSM-CCD considering carbon source (1–5%), pH (3–11) and temperature (25–65 °C) as matrix parameters. The optimum biosurfactant production (6.3 ± 0.1 g/L) and the minimum surface tension 29.85 mN/m were obtained after 96 h of incubation under optimal conditions i.e. 3.8% (v/v) of light-paraffin oil as sole carbon source at 62.4 °C and pH 7.7 with the maximum oil degradation cap- ability of 91.3 ± 5%. Critical micelle concentration value of crude biosurfactant was found to be 40 mg/L with high emulsification activity of 72.45 ± 0.85%. The produced biosurfactant was identified as lipopeptide (Surfactin) and characterized using various analytical techniques to establish its suitability for microbial en- hanced oil recovery. 1. Introduction The oil production from the oil reservoir fields happen in three methods; primary (5–10%), secondary (30–40%) and tertiary or en- hanced oil recovery. Various tertiary (enhanced) oil recovery ap- proaches are being investigated worldwide to recover residual oil after primary and secondary phase of oil extraction (Banat, 1995; Belyaev et al., 2004; Sen, 2008; Urum et al., 2004). In microbial enhanced oil recovery (MEOR) scheme, microorganisms (indigenous or injected in the reservoir) or their metabolites are used to retrieve the residual oil from oil reservoirs. The microbial metabolites may be biosurfactants (Iglauer et al., 2010; Sharma et al., 2018), biomass (Desai and Banat, 1997), biopolymers (Gudina et al., 2013), biosolvents (Fratesi, 2002), bioacids (Fratesi, 2002), biogases (carbon dioxide, methane, hydrogen) (Nerurkar et al., 2012). The EOR with the help of biosurfactants is considered to be one of the current strategies. Biosurfactants possess some unique properties of low toxicity, lower critical micelle con- centration (CMC), higher selectivity and its acceptable production economics (Chandankere et al., 2013; Liu et al., 2016; Thomas et al., 2013). Biosurfactants are surface active diverse group of molecules mainly consist of lipopeptides and lipoproteins, glycolipids, fatty acids, phospholipids, natural lipids, polymeric and particulate biosurfactants (Desai and Banat, 1997; Kiran et al., 2010). Among them, Surfactin, a cyclic lipopeptide, produced by different strains of Bacillus subtilis, is considered a potential biosurfactant due to its excellent surface activity required to mobilize the entrapped oil. Various biosurfactant producing novel strains have been isolated from different oil reservoir fields worldwide such as Enterobacter cloacae, Enterobacter hormaechei from formation water of southwest of Iran oil reservoirs (Rabiei et al., 2013), Pseudomonas aeruginosa SG from Xinjiang oilfield China (Zhao et al., 2016), Bacillus subtilis RI4914 from formation water of Brazilian oil field (Fernandes et al., 2016), Bacillus licheniformis from water samples from Niage field of Egypt (El- Sheshtawy et al., 2015), Pseudomonas aeruginosa (WJ-1), Bacillus subtilis (H10) and Rhodococcus erythropolis (Z25) from formation water of Chinese petroleum reservoir (Xia et al., 2011), and Bacillus subtilis B30 from petroleum contaminated soil samples in Oman (Al-Wahaibi et al., 2014). This indicated the presence and suitability of distinct bio- surfactant producing microorganisms in various geographical locations (Balan et al., 2017). Biosurfactant productions using various isolated https://doi.org/10.1016/j.biortech.2018.09.047 Received 9 July 2018; Received in revised form 7 September 2018; Accepted 8 September 2018 ⁎ Corresponding authors at: Centre for the Environment, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India. E-mail addresses: pankaj.tiwari@iitg.ac.in (P. Tiwari), lalitpandey@iitg.ac.in (L.M. Pandey). Bioresource Technology 270 (2018) 439–448 Available online 10 September 2018 0960-8524/ © 2018 Elsevier Ltd. All rights reserved. T