Phylogenetic and functional diversity of metagenomic libraries of phenol degrading sludge from petroleum refinery wastewater treatment system

Wastewater treatment plants (WWTP) represent habitats of continuous change in chemical composition (Szczepanowski et al. 2008). In oil refineries, the wastewater influent differs daily in terms of concentrations and composition of pollutant compounds, including light fraction aliphatic and aromatic petroleum hydrocarbons, organochlorines originated from cooling liquids used in the industrial process (Stepnowski et al. 2002) and other compounds such as phenol, chlorides, sulphides, sodium hydroxide, ammonia and heavy metals (Braile 1979; Mariano 2001). Phenols and derivatives are prominent pollutants in these wastes. These compounds are widely used as raw materials in the petrochemical industry and in oil refineries, for example in the washing and conditioning of alkaline or acid products. The increasing presence of phenols in the environment represents a serious ecological problem due to toxicity hazard for living creatures, including micro-organisms (Ojumu et al. 2005; Barrios-Martinez et al. 2006). Besides, the presence of phenols reduces significantly the biological degradation of the other compounds.Several processes are used to eliminate phenolic compounds from industrial wastewater, but the biological treatments have been preferred for large-scale removal. However, this is not an easy task because of the proper toxicity of phenol towards microorganisms (Barrios-Martinez et al. 2006). In this sense, the monitoring of the microbiota is very important for efficient performance of biological treatment systems.Traditionally, the diversity of microbial communities has been accessed by means of cultivation-based techniques or optical microscopy (Henze et al. 1997; Ojumu et al. 2005; Chang et al. 2005). Although very useful for taxonomic, physiological and genetic studies, culture-based techniques are insufficient for a more precise characterization of the functional and phylogenetic diversity of microbial communities, since it is now well known that only a small frac