Sequential Preconditioning and Its Effect on Crude Oil Bioremediation by Indigenous Soil Bacteria

Preconditioning has been proved to result in a significant increase in adaptability of biological organisms to adverse environmental stimulations and various stressful conditions. Accordingly, in a new approach attempt was made to enhance hydrocarbon degradation ability of selected potential isolates from a petroleum polluted soil through sequential adaptation. Firstly 8 isolates selected based on their growth at 5% (v/v) crude oil. Second selection performed based on their ability to adapt gradually them to 10%, 20% and 50% (v/v) crude oil concentration respectively, at simulated natural conditions (6.5 pH, 32°C). Isolates transferred to higher concentration of crude oil every 14 days. Their exponential growth rate served as an indicator of their adaptation success. Selected bacteria identified biochemically and morphologically according to Bergey's manual accompanied by 16s rRNA sequencing. Bacterial species were identified as P. putida, A. lwoffi, A. hydrophila, P. stutzeri, and A. johnsonii. Bacterial isolates were tested for their biodegradation ability individually and as a consortium; based on gas chromatographic analysis the consortium proved to be more efficient in n-alkane degradation as 93% of C8-C33 was removed in liquid cultures and 70% of hydrocarbons in artificially polluted soils, in 28 days. In addition ratios of n17/ pristane and n18/ phytane degradation supported the promising bioremediation ability of the consortium. Comparison between adapted and un-adapted bacteria revealed that aliphatic degradation enhanced up to 40% in soil. In general the results suggest that preconditioning bacterial isolates to higher oil concentration can significantly enhance their biodegradation ability especially as a consortium.