Indian Journal of Experimental Biology Vol. 53, May 2015, pp. 256-263 Enhanced Chrysene Degradation by a Mixed culture Biorem-CGBD using Response Surface Design Bharti P Dave * , Chirag M Ghevariya, Jwalant K Bhatt, Dushyant R Dudhagara & Rahul K Rajpara Department of Life Sciences, Sardar Vallabhbhai Patel Campus, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar, Gujarat-364 002, India Received 21 April 2014; revised 09 June 2014 Degradation of chrysene, a four ringed highly carcinogenic polycyclic aromatic hydrocarbon (PAH) has been demonstrated by bacterial mixed culture Biorem-CGBD comprising Achromobacter xylosoxidans, Pseudomonas sp. and Sphingomonas sp., isolated from crude oil polluted saline sites at Bhavnagar coast, Gujarat, India. A full factorial Central Composite Design (CCD) using Response Surface Methodology (RSM) was applied to construct response surfaces, predicting 41.93% of maximum chrysene degradation with an experimental validation of 66.45% chrysene degradation on 15 th day, using a combination of 0.175, 0.175 and 0.385 mL of OD 600 =1 inoculum of A. xylosoxidans, Pseudomonas sp. and Sphingomonas sp., respectively and a regression coefficient (R 2 ) of 0.9485 indicating reproducibility of the experiment. It was observed that chrysene degradation can be successfully enhanced using RSM, making mixed culture Biorem-CGBD a potential bioremediation target for PAH contaminated saline sites. Keywords: Biodegradation, Bioremediation, Carcinogenic, Mutagenic, PAH, Polycyclic aromatic hydrocarbons, RSM Polycyclic aromatic hydrocarbons (PAHs) are organic compounds with two or more fused aromatic rings in various structural configurations. Because of PAHs’ carcinogenic, mutagenic and teratogenic properties, they are of great environmental concern 1,2 . Though there are many chemical and physical approaches viz. landfilling, solvent extraction, high temperature incineration and chemical decomposition to destroy PAHs 3 , biodegradation is the major route for detoxification of PAH impacted environments 4 . The degradation of low molecular weight (LMW) PAHs such as naphthalene, phenanthrene and anthracene has been extensively studied and degradative pathways are well documented. However, knowledge of the ability of microorganisms to metabolize high molecular weight (HMW) PAHs is scarce 4 . Chrysene a four ringed carcinogenic HMW PAH with low water solubility is highly resistant to microbial attack, limiting the success of biodegradation. Thus, research on biodegradation study has focused on evaluating a wide diversity of microorganisms for their degradative abilities. This has led to identification of bacteria and fungi with an ability to degrade HMW PAHs by either partial degradation, co-metabolism, detoxification, biotransformation or by complete mineralization 5,6 . Indigenous microorganisms are observed to be efficient in degrading recalcitrant compounds, but an individual strain is incapable of complete degradation, due to its limited catabolic activities 7 . However, mixed cultures are more efficient due to their co-operative, cumulative and synergistic effects 8 . Syntrophic and complementing catabolic activities of mixed cultures can lead to elevated degradation rates which can result in complete removal of recalcitrant PAHs. The initial microbial strength is a crucial factor which affects degradation rates. When the population is small, or when it is unable to degrade mixture of PAHs, use of higher cell biomass can be an interesting approach. In contrast, where a native flora has adapted to recalcitrant PAHs, and stability established, an increase in cell biomass does not always result in increased degradation rates 9-11 . Central Composite Design (CCD) using Response Surface Methodology (RSM), which is a collection of mathematical techniques, is the most popular design applied to generate 3D plots to optimize conditions influenced by process variables, by plotting response surface and contour graphs. It has an added benefit over the traditional ‘one factor at a time’ approach —————— *Correspondence: Telefax: +91 278 2521545 E-mail: bpd8256@gmail.com