Bioremediation is based on microorganisms able to use pollutants either as a source of carbon or in co-metabolism, and is a promising strategy in cleaning the environment. Using soil contaminated with petroleum products from an industrial area in Saudi Arabia (Jubail), and after enrichment with the polycyclic aromatic hydrocarbon (PAH) naphthalene, a Methylobacterium radiotolerans strain (N7A0) was isolated that can grow in the presence of naphthalene as the sole source of carbon. M. radiotolerans is known to be resistant to gamma radiation, and this is the first documented report of a strain of this bacterium using a PAH as the sole source of carbon. The commonly reported Pseudomonas aeruginosa (strain N7B1) that biodegrades naphthalene was also identified, and gas chromatography analyses have shown that the biodegradation of naphthalene by M. radiotolerans and P. aeruginosa did follow both the salicylate and phthalate pathways.

Polycyclic aromatic hydrocarbons (PAHs) are significant pollutants found in petroleum products. There is ample literature on the biodegradation of PAHs containing less than five rings, but little has been done on those with more than five rings. Coronene (CRN), a seven-ring-containing PAH, has only been shown to be degraded by one bacterial strain. In this study, a bacterial strain 10SCRN4D was isolated through enrichment in the presence of CRN and 10% NaCl (w/v). Analysis of the 16S rRNA gene identified the strain as Halomonas caseinilytica. The strain was able to degrade CRN in media containing 16.5–165 μM CRN with a doubling time of 9–16 hours and grew in a wide range of salinity (0.5–10%, w/v) and temperature (30–50°C) with optimum conditions of pH 7, salinity 0.5%–10% (w/v), and temperature 37°C. Over 20 days, almost 35% of 16.5 μM CRN was degraded, reaching 76% degradation after 80 days as measured by gas chromatography. The strain was also able to degrade smaller molecular weight PAHs such as benzo[a]pyrene, pyrene, and phenanthrene. This is the first report of Halomonas caseinilytica degrading CRN as the sole carbon source in high salinity, and thus highlights the potential of this strain in bioremediation.