Biodesulfurization of benzonaphthothiophene by an isolated Gordonia sp. IITR100 Ashok Kumar Chauhan a , Abrar Ahmad a , Surya Pratap Singh b , Ashwani Kumar a, * a Environmental Biotechnology Division, Indian Institute of Toxicology Research (Council of Scientific & Industrial Research), M.G. Marg, Lucknow 226001, India b Department of Biochemistry, Faculty of Science, Banaras Hindu University, Varanasi, India article info Article history: Received 7 January 2015 Received in revised form 24 May 2015 Accepted 29 May 2015 Available online xxx Keywords: Biodesulfurization Gordonia sp. IITR100 Benzonapthothiophene Dibenzothiophene Crude oil abstract Studies on the desulfurization of three or more ringed-compounds, which are considered to inhibit biodesulfurization of crude oil, are rare. In this paper, desulfurization of a three-ringed compound benzo [b]naphtho[2,1-d]thiophene (BNT) by an isolated strain Gordonia sp. IITR100 is described. The bacterium mediates desulfurization of BNT and utilizes the released sulfur for its growth. The reaction is accom- panied with the formation of metabolites BNT-sulfone and BNT-sulfinate, in addition to the reported BNT-hydroxide. Recombinant E. coli cells, harboring DszC or DszA, were also able to mediate the metabolism of BNT to BNT-sulfone, or of BNT-sulfone to BNT-sulfinate, respectively. Desulfurization of BNT, both by IITR100 and E. coli-DszC cells was strongly inhibited in the presence of dibenzothiophene. The results are discussed in the context of the biodesulfurization of petroleum fractions where several organosulfur compounds are present together. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Numerous organosulfur compounds are present in the petro- leum products (Liu et al., 2010), and pose various serious problems e.g. (i) sulfurous emissions in the air upon their burning, causing health problems and acid rain (ii) souring of refinery equipment, and (iii) increase in viscosity of a large fraction of crude oil, rendering it non-amenable to refinery process (Korte and Boedefeld, 1978; Lewtas, 2007). Biodesulurization is an attractive option for reduction of the sulfur content of crude-oil and its fractions (Kilbane, 2006). Studies with the model compound dibenzothiophene (DBT) and its derivatives have revealed that the desulfurization occurs by a ‘4S’ pathway that includes serial activity of the enzymes DszC, DszA and DszB, resulting in the formation of hydroxy-biphenyl as end product (Gallagher et al., 1993; Oldfield et al., 1997; Santos et al., 2007; Mohebali and Ball, 2008). Genes for these proteins i.e. dszC, dszA and dszB have been characterized from several organisms, where these are present together as dszABC in an operon and are co-ordinately regulated (Denome et al., 1994; Mohebali and Ball, 2008). Pathway for the desulfurization of ben- zothiophene, at least in part, is analogous to the ‘4S’ pathway and formation of the metabolites BT-sulfoxide & BT-sulfone has been reported (Gilbert et al., 1998; Tanaka et al., 2001). Metabolism of BT- sulfone is followed with the formation of benzo[c][l,2]oxathiin S- oxide that undergoes transformation into either 2-(2 0 -hydrox- ypheny1) ethan-1-al (Kilbane, 2006) or o-hydroxystyrene (Tanaka et al., 2001), as seen in the strains Gordonia sp. 213E and Sino- rhizobium sp. KT55, respectively. Recently, three genes designated as bdsABC, which are distinct from dszABC that were identified earlier for DBT-desulfurization, have been characterized from a Gordonia terrae strain C-6, whose products mediate the trans- formation of BT into o-hydroxystyrene (Wang et al., 2013). Many of the isolated organisms have also been shown to mediate the desulfurization of crude oil and its various fractions. In most cases, while the desulfurization of light-oil fractions is reasonable (~95%), the desulfurization of various crude oil is modest (~50%) (Kilbane, 2006; Mohebali and Ball, 2008; Bhatia and Sharma, 2010, 2012). It is now recognized that the desulfurization of heavy oils is inhibited progressively in the presence of increasing concentrations of the three- or more ringed-sulfur compounds (Choudhary et al., 2008). Studies on these compounds, however, are scarce. The organisms Bacillus subtilis WU-S2B (Kirimura et al., 2001) and Rhodococcus erythropolis XP (Yu et al., 2006) have been * Corresponding author. E-mail addresses: ashokchauhan44@gmail.com (A.K. Chauhan), abrar.ahmadg@ yahoo.com (A. Ahmad), ssingh35@bhu.ac.in (S.P. Singh), ashwani.iitr26@gmail. com (A. Kumar). Contents lists available at ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod http://dx.doi.org/10.1016/j.ibiod.2015.05.024 0964-8305/© 2015 Elsevier Ltd. All rights reserved. International Biodeterioration & Biodegradation 104 (2015) 105e111