ENVIRONMENTAL BIOTECHNOLOGY Optimization and modeling of phenanthrene degradation by Mycobacterium sp. 6PY1 in a biphasic medium using response-surface methodology Arwa Abdelhay & Jean-Pierre Magnin & Nicolas Gondrexon & Stéphane Baup & John Willison Received: 8 November 2007 / Revised: 10 January 2008 / Accepted: 12 January 2008 / Published online: 7 February 2008 # Springer-Verlag 2008 Abstract In the present paper, the degradation of phenan- threne, a model polycyclic aromatic hydrocarbon com- pound, by the Mycobacterium strain 6PY1 was optimized in a biphasic culture medium. The optimization and modeling were performed using the design of experiments methodology. The temperature, the silicone oil/mineral salts medium volume ratio, and the initial cell concentration, were used as the central composite design parameters. In all experiments, the phenanthrene was degraded to undetect- able levels. Response surface methodology was successful- ly employed to derive an empirical model describing the rate and time of degradation and to deduce the optimal degradation conditions. As a result of the optimization processes, the optimal responses for the degradation rate, the volumetric degradation rate, and the 90% degradation time were estimated to be 0.172 mg h -1 , 22 mg l -1 h -1 , and 18 h, respectively. Keywords Polycyclic aromatic hydrocarbons . Phenanthrene . Mycobacterium . Biodegradation . Biphasic culture . Design of experiments Introduction Polycyclic aromatic hydrocarbons (PAHs) are environmental- ly ubiquitous and recalcitrant organic contaminants produced naturally or as a result of incomplete combustion of organic materials. The persistence of PAHs is an environmental concern and has attracted much attention because many of these compounds have been reported to be carcinogenic and mutagenic (Cerniglia 1992; Cerniglia 1993). Many approaches have been proposed to destroy or render this type of contaminant, such as landfilling, solvent extraction, high-temperature incineration, and various types of chemical decomposition (Jonker and Koelmans 2002; Ledakowicz et al. 1999; Yip et al. 2006). However, bioremediation has been considered as a promising potential option for PAH elimina- tion in comparison to the previously conventional practices. As such, it uses relatively low-cost, low-technology tech- niques, which generally have a high public acceptance and can often be carried out on-site (Vidali 2001). In this context, many review articles have described the ability of numerous soil microorganisms to biotransform and mineralize PAHs (Prabhu and Phale 2003; Kim et al. 2005). Among them, mycobacteria oxidize the greatest variety of PAHs (Boldrin et al. 1993; Miyata et al. 2004; Churchill et al. 1999; Cerniglia 2003; Guerin and Jones 1988). Improving this Appl Microbiol Biotechnol (2008) 78:881–888 DOI 10.1007/s00253-008-1365-x A. Abdelhay (*) Laboratoire d’Electrochimie at de Physico-chimie des Matériaux et des Interfaces (LEPMI), Institut National Polytechnique de Grenoble, ENSEEG, nº 1130 rue de la Piscine, BP 75, Domaine Universitaire 38402 Saint-Martin d’Heres Cedex, France e-mail: arwa.abdelhay@lepmi.inpg.fr J.-P. Magnin Laboratoire d’Electrochimie et de Physico-chimie des Matériaux et des Interfaces (LEPMI), Centre National de la Recherche Scientifique (CNRS), ENSEEG, nº 1130 rue de la Piscine, BP 75, Domaine Universitaire 38402 Saint-Martin d’Heres Cedex, France N. Gondrexon : S. Baup Laboratoire d’Electrochimie et de Physico-chimie des Matériaux et des Interfaces (LEPMI), Université Joseph Fourier, ENSEEG, nº 1130 rue de la Piscine, BP 75, Domaine Universitaire 38402 Saint-Martin d’Heres Cedex, France J. Willison IRTSV, Laboratoire de Chimie et Biologie des Métaux (LCBM), CEA Grenoble 17 rue des Martyrs 38054, Grenoble cedex 9, France