Abstract
Contamination of the environment by high-molecular-weight polycyclic aromatic hydrocarbons (HMW-PAH) occurs in hypersaline conditions, mainly in produced water derived from petroleum extraction, and biological treatment offers an attractive option to remove these pollutants. This study aimed at isolating and characterizing bacteria that biodegrade HMW-PAH pyrene in a halophilic environment. Two bacteria, 10PY2B and 20PY1A, were isolated by enrichment culture in 10% and 20% NaCl, respectively, in the presence of pyrene as the sole source of carbon. Using 16S rRNA analyses, 10PY2B was identified as Halomonas shengliensis and 20PY1A as Halomonas smyrnensis. These strains had doubling times of less than 24h when pyrene was used at concentrations <50ppm, making them as rapidly growing pyrene-biodegrading bacteria as the reference strain Mycobacterium vanbaalenii. 10PY2B and 20PY1A were more active at neutral to alkaline conditions, and at 25 degrees C, efficiently biodegraded aromatic compounds of lower molecular weight than pyrene (sodium salicylate, naphthalene, phenanthrene, and anthracene). Within 18 days, the strains had biodegraded 50% of 50ppm pyrene, and gas chromatography/mass spectroscopy led to identification of the metabolites 4-phenanthrenecarboxylic acid, 4-(1-hydroxynaphthalen-2-yl)-2-oxo-but-3-enoic acid, and phthalic acid. A possible pathway for pyrene biodegradation has been proposed based on these metabolites.