534 Journal of Basic Microbiology 2007, 47, 534 – 539 © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jbm-journal.com Research Paper Hydrocarbon degradation by thermophilic Nocardia otitidiscaviarum strain TSH1: physiological aspects Majid Zeinali 1 , Manouchehr Vossoughi 2 , Sussan K. Ardestani 1 , Esmaeil Babanezhad 3 and Mohamadreza Masoumian 4 1 Institute of Biochemistry and Biophysics (IBB), University of Tehran, Tehran, Iran 2 Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran 3 Department of Chemistry, Sharif University of Technology, Tehran, Iran 4 Faculty of Applied Sciences, Malek-Ashtar University of Technology, Tehran, Iran Indigenous thermophilic hydrocarbon degraders are of special significance for the bioreme- diation of oil-contaminated desert soils with ambient temperature of 45 – 50 °C. The first objective of this study was to demonstrate the hydrocarbon-degrading capability of Nocardia otitidiscaviarum TSH1 (DSM 45036) which grows optimally at 50 °C. Analysis of the metabolic profile of the strain TSH1 showed that it could metabolize phenol, intermediate-chain-length n-alkanes and some polycyclic aromatic hydrocarbons (PAHs) ranging in size from two to four fused rings efficiently, but not toluene and xylene. N. otitidiscaviarum TSH1 was able to survive and grow at phenol concentrations up to 875 mg l –1 . For the first time, the physiological response of a thermophilic Nocardia strain to poorly available hydrophobic compounds was also investigated. When grown on a mineral salt medium with hexadecane, N. otitidiscaviarum TSH1 showed very high affinity for the organic phase. Additionally, PAH-grown cells were considerably hydrophobic. The capacity of PAH-utilizing N. otitidiscaviarum TSH1 isolate to produce biosurfactants was also investigated. Fatty acids (C 14 –C 18 ) were detected by GC-MS analysis during bacterial growth in PAH supplemented mineral media. High cell surface hydrophobicity and capability of N. otitidiscaviarum TSH1 to degrade different hydrocarbons at 50 °C may make it an ideal candidate to treat oil-contaminated desert soils. Keywords: Thermophile / Nocardia otitidiscaviarum / PAHs / Phenol / Straight-chain alkanes Received: September 05, 2007; accepted: September 19, 2007 DOI 10.1002/jobm.200700283 Introduction * Crude oils are composed of mixtures of hydrocarbons, including n- and branched-chain alkanes, cycloalkanes, monoaromatics, phenolic and polycyclic aromatic hy- drocarbons (PAHs). Therefore, many petroleum con- taminated sites are characterized by the presence of complex mixtures of pollutants. Microbial degradation is the major mechanism for the elimination of spilled oil from the environment but the success of bioreme- Correspondence: Manouchehr Vossoughi, Department of Chemical and Petroleum Engineering, Sharif University of Technology, Azadi Ave., Tehran, Iran E-mail: vosoughi@sharif.ir Tel.: +98 (21) 66165487 Fax: +98 (21) 66005417 diation techniques will depend on the ability of bacte- ria to degrade all of the components of crude oils. Thermophiles possess a substantial potential for the conversion of all major classes of environmental pol- lutants. On the other hand, thermophilic microorgan- isms can serve as excellent sources for more thermo- stable biocatalysts than presently available [1]. Since elevated temperatures can increase solubility, mass transfer rates and the enzyme activities involved in the biodegradation of oil hydrocarbons, indigenous ther- mophilic hydrocarbon degraders are of special signifi- cance for the bioremediation of oil-polluted desert soils [2]. Substrate utilization rates of thermophilic bacteria have been reported to be 3 to 10 times greater than those observed with the mesophilic bacteria [3].