Isolation and characterization of PAH degrading bacteria from polluted Venice lagoon

Polycyclic aromatic hydrocarbons (PAHs) are contaminants widely distributed in the environment. Many PAH are highly toxic to microorganisms as well as to humans. To contain and detoxify PAH-contaminated environment several technologies have been developed. Considerable efforts have recently focused on the isolation of microorganisms able to degrade PAHs producing less harmful and non-hazardous substances that are then integrated into natural biogeochemical cycles. This process, known as Bioremediation, is a non-destructive, cost- and treatment-effective. The aim of this study was the isolation of microbial communities from Italian contaminated sediments (Gran Canal of Venice Lagoon) and the characterization of their ability to degrade the PAHs present in this site. We used naphthalene as model compound because it is the simplest, the most soluble PAH and it is a common component of the aromatic fraction of pollutants. Different communities of bacteria were isolated and characterized based on microbiological and biochemical tests. Among them 3 bacterial species were able to use naphthalene as a sole carbon source both in liquid and solid media. Phylogenetic analysis performed on 16S rRNA gene indicated that these strains belong to the species of Shewanella algae (LCS1, facultative anaerobes), Pseudomonas aeruginosa (LCS9, aerobes) and Pseudomonas fluorescens (LCC11, aerobes). The ability of these bacteria to metabolize naphthalene was determined by measuring the activity of enzymes of naphthalene degradation pathway. We found that the activity of salicylaldheyde dehydrogenase and salycilate hydroxylase enzymes, catalysing the reactions of the last steps of naphthalene degradation pathway, was significantly induced in the selected strains. We think that the selected microbial consortium, consisting of two aerobes strains and one facultative anaerobe strain, has a promising potential for the development of new strategies in environmental bioremediation, and in particular in the treatment of polluted sediments in which both oxic (surface) and anoxic (bottom) layers are present.