Enhanced biodegradation of crude oil contamination by indigenous bacterial consortium under real conditions

This study was performed to evaluate the efficiency of using locally isolated bacteria to degrade crude oil in sea water-based medium. The bacteria were isolated from water samples taken from different sea environments (Mediterranean, Aegean, Marmara, and Black Sea). The experiments for crude oil degradation were carried out in small volume (100 mL sea water medium in 250 mL shaking flasks) or large volume (14 L sea water-based medium in a plastic container). Furthermore, the media were not sterilized and remained open to the environment (non-sterile conditions). On the other hand, the media were shaken at a low speed of 50 rpm to mimic sea conditions. Of twelve bacterial isolates, four isolates (PB1, PB4, PB6, and PB7) having higher oil degradation potential were selected. According to 16S rRNA analysis, the isolates PB4 and PB6 were identified as, respectively, Rhodococcus qingshengii and Alcanivorax venustensis, and the other two isolates (PB1 and PB7) as Pseudomonas sabulinigri. When the usability of four isolates alone or as a co-culture for crude oil degradation was tested, co-cultures were found to cause more crude oil degradation than individual bacterial cultures. Among the co-cultures, the maximum degradation of crude oil was achieved with the association of PB6 + PB4. During the experiments, carbon sources and minerals were not supplemented to the sea water medium, and even the supplementation of only nitrogen source (especially ammonium sulphate) was determined to significantly enhance the crude oil degradation potential of the bacterial consortium (PB6 + PB4). Spectrophotometric analyses (OD225) demonstrated that crude oil degradation continued up to 12th day in small volume but 16th day in large volume. GC-MS analyses revealed that co-culture of PB6 and PB4 degraded 100% of C9-C12 and C16-C29 hydrocarbons and 85% of C13-C15 hydrocarbons.