Bioremediation of two oil-contaminated Kuwaiti hyper-saline soils by cross bioaugmentation and the role of indigenous halophilic/halotolerant hydrocarbonoclastic bacteria

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Hyper-saline evaporitic sandflats known as Sabkhas occur in areas prone to oil contamination throughout the Gulf states. Bioaugmentation of Sabkha environments using enrichments of indigenous microorganisms is a potential means of ameliorating oil pollution. Two soil samples from the north and south Kuwaiti Sabkhas were contaminated with 5% w/w oil to prepare inocla enriched with hydrocarbonoclastic bacteria. Inocula were then used in a 6-month cross-bioaugmentation process to assess oil bioremediation in two artificially oil-contaminated soils collected from the same Sabkhas. Although the numbers of hydrocarbonoclastic bacteria increased and oil degradation was observed in both unbioaugmented and bioaugmented samples for both locations, bioaugmentation significantly enhanced degradation at only one location. The predominant culturable strain Bacillus oceanisediminis in the enriched inocula failed to colonize the bioaugmented soils in both locations. For further insight into oil biodegradation by Sabkha bacteria, sixteen hydrocarbonoclastic isolates were recovered and their oil biodegradation potential was recognized under different salinity conditions. All isolates tolerated up to 10% w/v salinity and most still grew at up to 18% and showed maximum oil consumption at their optimal salinity requirement. To simulate a serious pollution event, the potential response of Sabkha soils after high oil contamination reached 20% was tested, and this indicated both soils showed a significant self-cleaning potential at this high pollutant level. Overall, we conclude that bioremediation of contaminated hyper-saline soils depends mainly on the allochthonous halotolerant/halophilic hydrocarbonoclastic bacteria adapted to their native area, and the potential for microbial bioremediation even under high contamination levels is potentially high.