Comparison of Hydrocarbon-Degrading Consortia from Surface and Deep Waters of the Eastern Mediterranean Sea: Characterization and Degradation Potential

The Eastern Mediterranean Sea (EMS) has attracted great interest in recent years due to large oil and gas reservoirs that have been discovered in deep and ultra-deep waters. A potential oil spill accident, similar to that of Deepwater Horizon in the Gulf of Mexico, could have severe impact in the marine life and economy of the surrounding countries in Eastern Mediterranean basin. Here, the diversity and degradation capacity of hydrocarbon-degrading consortia enriched from surface (10m) and deep (1040m) waters of EMS, were studied in a series of experiments. Microcosms were set up in ONR7a medium at in situ temperatures, 25°C and 14°C for Surface and Deep sea consortia respectively with crude oil as the sole carbon source. The Deep sea consortium was additionally investigated at 25° C to allow the direct comparison of degradation rates to the Surface consortium. By the end of the experiment, ~50% of alkanes and ~15% of polycyclic aromatic hydrocarbons were degraded in all treatments. Approximately ~95% of the total biodegradation by the Deep consortium took place within 6 days regardless of temperature, whereas comparable levels of degradation were reached on day 12 by the Surface consortium. Both consortia were dominated by well-known hydrocarbondegrading taxa. Temperature played a significant role in shaping the Deep sea consortia communities with Pseudomonas and Pseudoalteromonas dominating at 25°C and Alcanivorax at 14°C. Overall, the Deep sea consortium exhibited a higher efficiency for hydrocarbon degradation within the first week following contamination, which is critical in the case of oil spills and thus, further investigation is required to arrive at site-specific bioremediation technologies exploiting the characteristics of deep sea consortia.