University of Khartoum

Assessment of Selected Tree Species and their Rhizospheric Bacteria for Bio-Remediation of Petroleum Hydrocarbon- Contaminated Soil

Assessment of Selected Tree Species and their Rhizospheric Bacteria for Bio-Remediation of Petroleum Hydrocarbon- Contaminated Soil

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Title: Assessment of Selected Tree Species and their Rhizospheric Bacteria for Bio-Remediation of Petroleum Hydrocarbon- Contaminated Soil
Author: Mohammed, Amel Hassan Abdallah
Abstract: The objective of this study was to test the abilities of Acacia seyal, A. polycantha, A. sieberiana, Balanites aegyptiaca and parkinsonia aculeata with their associated rhizobacteria to remediate crude oil contaminated soil under laboratory conditions. Seedlings of each tree species were transplanted and grown in a set of four polyethylene bags (29X20cm) each containing three kg sand soil contaminated with crude oil at concentrations (%) of 0.5, 1.00, 1.5 or 2.00 for 180 days. A set of seedlings for each tree species was also raised, as a control, in oil- free soil and the experiment was laid out in a completely randomized design with three replicates. Plant growth parameters were measured at two, four and six month intervals. At zero time and then at the mentioned intervals individual hydrocarbons present were determined, using GC-MS, in soil contaminated with 0.5 % crude oil and planted with A.sieberiana seedlings. Also, at six month interval total hydrocarbon residue in soil was determined and oil degradation percentages, as compared to the control, were calculated. Viable counts of dominant bacteria in rhizospheric oil –contaminated and non- contaminated soils were determined at different intervals using two media viz starch ammonium agar and meat peptone agar. The most dominant bacterial colonies were repeatedly subcultured for purification and characterized by standard microscopic and biochemical procedures. These isolates were screened for their abilities to degrade crude oil using Bushnel Hass Medium contaminated with 0.5 and 1.0% oil. The most efficient oil degraders were identified to the strain level by partial sequencing of 16srRNA gene. In general, the performance of the studied tree species under oil stress at different oil concentrations and different intervals was significantly (P≤ 0.05) better than that of the control as indicated by one or more of the growth parameters measured . Oil concentrations of up to 2.0, 1.5, 1.0 and 0.5 per cent has been well tolerated by A.sieberiana, A.polycantha, B.aegyptiaca , P.aculeata and A.seyal, respectively. Shoot length and shoot and root weight have not been negatively affected by oil, compared to the control , up to a concentration of 1.5% for up to six months. Crude oil degradation percentages were found to be in the range of 49-79%. The highest degradation percentage was recorded for the soil collected from underneath A.sieberiana seedlings (79%) followed by A.polycantha (76%) and B.aegyptiaca (74%). However, per cent degradation values comparable to the control (49%) were recorded for soil samples taken from rhizospheric soil of P.aculeata (55%) and A.seyal (54%). A total of 81 different hydrocarbons were detected in soil samples at zero time and most of them were found to be of long (≥ 30 carbon atoms) and moderate (10-29 C) hydrocarbon chains, the most abundant of which were hentriacontane, heneicosane, nonadecane, heptadecane and hexadecane. Of the 81 hydrocarbon detected at zero time, only 15, 9 and 19 were detected at 60,120 and 180 days intervals, respectively. Thirty eight and 22 compounds, which were considered as the degradation products of more complex compounds originally present in the crude oil, were detected at 60 and 180 days sampling intervals, respectively. Viable microorganism’s count in oil-contaminated soil at any of the concentrations tested was significantly (P≤0.01) higher than that in oil free soil at any sampling interval. Nine of the 21 recovered isolates were found to grow in Bushnel Haas mineral salt medium and were also found to produce proteins and to lower both medium pH and surface tension, characteristics which support the use of these isolates for oil degradation trials under field conditions. The most efficient oil degraders (isolate 3kok15 and kt con.A) were identified to the species level as Bacillus anthracis str. Ames and Streptomyces minutiscleroticus str.NRRLB.12202. To the best of our knowledge, this is the first report on these two bacterial species to be involved in biosurfactants production and degradation of crude oil. Future research to evaluate oil degradation potential of A .sieberiana under field conditions and to explore the oil degradation pathways by the potential bacterial isolates is recommended.
URI: http://khartoumspace.uofk.edu/123456789/25978


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