A STUDY OF THE BIOTECHNOLOGICAL APPLICATIONS OF NOVOSPHINGOBIUM PUTEOLANUM PP1Y.

Abstract

Environmental pollution caused by the release of a wide range of xenobiotic compounds has assumed serious proportions. Bioremediation techniques, utilizing microorganisms to reduce the concentration and toxicity of various chemical pollutants such as petroleum hydrocarbons, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, industrial solvents and pesticides, are the most promising strategies for the restoration of polluted environments. Several bacterial strains with promising degradative abilities have already been isolated and characterized. However, the full exploitation of the potential of bioremediation strategies requires not only the isolation of a large number of strains with wide degradative abilities but also an accurate characterization of these strains both at the microbiological and biochemical/genetic level. This knowledge is necessary to perform a rational planning of bioremediation interventions. The present work describes isolation of new strains able to degrade aromatic hydrocarbons directly from polluted environments by means of appropriate selection procedures. Novosphingobium sp. PP1Y, isolated from a surface seawater sample collected from a closed bay in the harbor of Pozzuoli (Naples, Italy), uses fuels as its sole carbon and energy source. Like some other Sphingomonads, this strain can grow as either planktonic free cells or sessile-aggregated flocks. In addition, this strain was found to grow as biofilm on several types of solid and liquid hydrophobic surfaces including polystyrene, polypropylene and diesel oil. Strain PP1Y is not able to grow on pure alkanes or alkane mixtures but is able to grow on a surprisingly wide range of aromatic compounds including mono, bi, tri and tetracyclic aromatic hydrocarbons and heterocyclic compounds. During growth on diesel oil, the organic layer is emulsified resulting in the formation of small biofilm-coated drops, whereas during growth on aromatic hydrocarbons dissolved in paraffin the oil layer is emulsified but the drops are coated only if the mixtures contain selected aromatic compounds, like pyrene, propylbenzene, tetrahydronaphthalene and heterocyclic compounds. These peculiar characteristics suggest strain PP1Y has adapted to efficiently grow at the water/fuel interface using the aromatic fraction of fuels as the sole carbon and energy source. The whole PP1Y genome sequence could provide clues about the metabolism of this species and about the possibility of manipulating it for bioremediation purposes. The PP1Y genome is comprised of a single 3.9 Mbp circular chromosome and of 3 plasmids, one megaplasmid (Mpl; 1.16 Mbp), one large plasmid (Lpl; 0.19 Mbp), and one small plasmid (Spl; 0.05 Mbp). Notably, this is the first time that a megaplasmid of such size has been identified in a sphingomonad. Our results will help to clarify the molecular basis of the unusual features of this strain and to engineer strains with enhanced cultural and bioremediation abilities.