International Research Journal of Applied and Basic Sciences. Vol., 3 (1), 138-147, 2012 Available online at http://www. irjabs.com ISSN 2251-838X ©2012 Assessment of biodegradation efficiency of some isolated bacteria from oil- contaminated sites in solid and liquid media containing oil-compounds M. Ebrahimi 1 , M.R. Sarikhani 2* and R. Fallah 3 1- Master of soil science, Mtrr_ebrahimi@yahoo.com 2- Department of Soil Science, Faculty of Agriculture, University of Tabriz, Tabriz, Iran 3- Institute of Soil & Water research, Karaj, rezafayah@yahoo.com * Corresponding author, Tel.:+98-411-339 2023. E-mail address: rsarikhani@yahoo.com. ABSTRACT: Oil contamination in Iran due to high application of oil compounds, is one of the most dangerous pollution factors. Bioremediation is one of principal strategies for remediation, where in the pollutants can be removed by use of microorganism or any biological process that uses microorganisms or their enzymes to return the environment altered by contaminants to its original condition. With regards to the importance of bioremediation, hydrocarbon degrading efficiency of some isolated bacteria from oil- polluted sites of Bushehr province, such as Pseudomonas stutzeri, Pseudomonas alcaligenes, Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Serattia odorifera, Achromobacter xylosoxidans, Acinetobacter johnsonii, Entrobacter cloacae, Ralstonia sp., Vibrio sp., Sphingobacterium sp., Zymomonas sp., Paracoccus sp., Pantoea sp. and Chryseobacterium sp. were determined in a solid and liquid medium enriched by gas oil (2%), toluene (1%) and phenanthrene (0.05%). In order to determine the efficiency of these bacteria in hydrocarbon-degrading an inoculum of bacteria containing 10 8 cfu/ml was used in plate and liquid assays, which were performed in factorial experiment based on completely randomized design with 3 replications. The increasing of diameter of colony and the growth turbidity (OD 600nm ) as indicators for utilization of hydrocarbon was measured in solid and liquid assays, respectively. Results showed that in CFMM plate assay, highest diameter of colony in presence of toluene and phenanthrene were achieved by Chryseobacterium sp. and Sphingobacterium sp., while in liquid assay and in presence of three compounds Serattia odorifera and Entrobacter cloacae were efficient. Moreover, among three compounds highest degradability in bioremediation was related to gas oil, and it’s followed by phenanthrene and toluene, respectively. Keywords: Bioremediation; Oil contamination; Gas oil; Toluene; Phenanthrene INTRODUCTION Biological and non-biological approaches are being used for remediation of oil-pollution. Bioremediation is one of principal strategies for remediation, wherein the pollutants can be removed by use of microorganism or any biological process that uses microorganisms or their enzymes to return the environment altered by contaminants to its original condition (Olu-Arotiowa et al., 2007; Supaka et al., 2001). Many species of microorganisms including bacteria, yeasts and fungi obtain both energy and tissue-building material from petroleum. Petroleum is a complex mixture of aliphatics, aromatics, resins and asphaltenes (Cohen, 2002). Hydrocarbon products contain a mixture of different components and differ in their susceptibility to microbial attack and generally degrade in the following order of decreasing susceptibility: n-alkanes >branched alkanes >low-molecularweight aromatics >cyclic alkanes (Leahy and Colwell, 1990). Fortunately, bacteria are able to feed upon the wide variety of compounds found in petroleum. The ability of many microorganisms in order to biodegradation of hydrocarbons has been studied (Mesdaghinia et al., 2005; Liangli and Hungchen, 2009; Sarikhani et al, 2011). Rashid Ashmasg and coworkers (2009) in a study isolated Acinetobacter from oil-polluted soil and investigated its ability in