Characterization of Halophilic Bacteria Capable of Efficiently Biodegrading the High-Molecular-Weight Polycyclic Aromatic Hydrocarbon Pyrene

Contamination of the environment by high-molecular-weight PAH (HMW-PAH) occurs in hypersaline conditions, mainly in produced water derived from petroleum extraction, and biological treatment offers a potential option to remove these pollutants. 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 24 hr when pyrene was used at concentrations <50 ppm, 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°C, efficiently biodegraded aromatic compounds of lower molecular weight than pyrene (sodium salicylate, naphthalene, phenanthrene, and anthracene). Within 18 d, the strains had biodegraded 50% of 50 ppm pyrene, and GC/MS identified 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.