BackgroundBiodegradation is a cheap and environmentally friendly process that could breakdown and utilizes heavy crude oil (HCO) resources. Numerous bacteria are able to grow using hydrocarbons as a carbon source; however, bacteria that are able to grow using HCO hydrocarbons are limited. In this study, HCO degrading bacteria were isolated from an Omani heavy crude oil field. They were then identified and assessed for their biodegradation and biotransformation abilities under aerobic and anaerobic conditions.ResultsBacteria were grown in five different minimum salts media. The isolates were identified by MALDI biotyper and 16S rRNA sequencing. The nucleotide sequences were submitted to GenBank (NCBI) database. The bacteria were identified as Bacillus subtilis and B. licheniformis. To assess microbial growth and biodegradation of HCO by well-assay on agar plates, samples were collected at different intervals. The HCO biodegradation and biotransformation were determined using GC-FID, which showed direct correlation of microbial growth with an increased biotransformation of light hydrocarbons (C12 and C14). Among the isolates, B. licheniformis AS5 was the most efficient isolate in biodegradation and biotransformation of the HCO. Therefore, isolate AS5 was used for heavy crude oil recovery experiments, in core flooding experiments using Berea core plugs, where an additional 16 % of oil initially in place was recovered.ConclusionsThis is the first report from Oman for bacteria isolated from an oil field that were able to degrade and transform HCO to lighter components, illustrating the potential use in HCO recovery. The data suggested that biodegradation and biotransformation processes may lead to additional oil recovery from heavy oil fields, if bacteria are grown in suitable medium under optimum growth conditions.
Crude oil contamination is one of the major environmental concerns and it has drawn interest from researchers and industries. Heavy oils contain 24-64% saturates and aromatics, 14-39% resins and 11-45% asphaltene. Resins and asphaltenes mainly consist of naphthenic aromatic hydrocarbons with alicyclic chains which are the hardest to degrade. Crude oil biodegradation process, with its minimal energy need and environmentally friendly approach, presents an opportunity for bioremediation and as well for enhanced oil recovery to utilize heavy oil resources in an efficient manner. Biodegradation entails crude oil utilization as a carbon source for microorganisms that in turn change the physical properties of heavy crude oil by oxidizing aromatic rings, chelating metals and severing internal bonds/chains between molecules. Biodegradation does not necessarily lower quality of crude oil as there are cases where quality was improved. This paper provides information on heavy crude oil chemistry, bioremediation concept, biodegradation enzymes, cases of Microbial Enhanced heavy crude Oil Recovery (MEOR) and screening criteria towards a better understanding of the biodegradation application. Through the utilization of single microorganisms and consortia, researchers were able to biodegrade single pure hydrocarbon components, transform heavy crude oil fractions to lighter fractions, remove heavy metals and reduce viscosity of crude oil.
Abundance of heavy crude oil resources and costly enhanced oil recovery (EOR) techniques necessitate development of inexpensive heavy oil recovery methods. Microbial EOR (MEOR) techniques are environmentally friendly and need little input of energy to produce MEOR agents. One potential application of MEOR is in the biotransformation of heavy oil where bacteria break heavier fractions of heavy crude oil to lighter compounds; thus, improving oil recovery. In this study, two spore forming bacteria: Bacillus subtilis AS2 and Bacillus licheniformis AS5, which were isolated from heavy oil (13.3 °API) contaminated soil samples from a heavy oil field, Oman, were tested for their biotransformation abilities. Bacterial growth was analyzed by optical density measurements and heavy crude oil recovery was determined by core flooding experiments. At aerobic biodegradation flask experiments, M2 medium spiked with glucose had the highest bacteria growth and crude oil biodegradation in comparison with: (1) M2 medium with no added chemicals and (2) M2 medium spiked with sodium thiosulfate. At anaerobic in situ conditions Berea sandstone core flooding experiments, additional 2.9% and 3.1% of residual oil saturation was recovered by B. subtilis AS2 and B. licheniformis AS5 respectively after one week of incubation. By increasing the incubation time and inoculation percentage for isolate AS5, the oil recovery increased to 5.0%. When glucose was added to M2 medium, AS5 oil recovery increased to 16.4%.The results showed that locally isolated bacterial strains have the potential for biotransformation of heavy oil and enhanced oil recovery.
Here, we report the draft genome sequence of Bacillus subtilis AS2 that was isolated from heavy crude oil-contaminated soil samples from sludge pits of an Omani heavy-oil field. B. subtilis AS2 was able to biodegrade heavy crude oil and produce biosurfactant. In order to provide a better understanding of the biodegradation mechanism and biosynthesis of metabolites, the B. subtilis AS2 genome was sequenced and compared to those of other B. subtilis strains.
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