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Bacterial Community Structure Change Induced by Gamma Irradiation in Hydrocarbon Contaminated and Uncontaminated Soils Revealed by PCR-Denaturing Gradient Gel Electrophoresis

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Author(s): Wael S. El-Sayed | S. Ghanem

Journal: Biotechnology
ISSN 1682-296X

Volume: 8;
Issue: 1;
Start page: 78;
Date: 2009;
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Keywords: DGGE | contaminated soil | soil bacteria | Gamma irradiation

ABSTRACT
The effect of gamma irradiation on bacterial community structure in garden clay, uncultivated clay and hydrocarbon contaminated soils were investigated by exposing soils to various doses of ionizing radiation using a Co-60 source. Bacterial community structure in irradiated soils was examined 30 days after irradiation at 1, 2, 3, 4, 5 and 10 kGy doses. Gamma irradiation was found to have a selective impact on the microbial community structure in certain soils. Sensitivity to irradiation varies among microbial species and is affected by the properties of the soil. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA gene fragments amplified from the three soils were performed. Bacterial population in garden clay soil was stimulated by low irradiation doses and sharply decreased at higher doses. Phylogenetic analysis revealed predominance of only cloroflexi bacterium at elevated doses of irradiation in garden clay soil. In uncultivated clay soil, much of the bacterial populations were affected by irradiation treatment, however, two representatives of gammaproteobacteria, Enterobacter sp. and Pseudomonas sp. showed some resistance to irradiation and were present at all irradiation doses. DGGE profile suggested that bacteria in hydrocarbon contaminated soil were more resistant to irradiation than garden and/or clay soils. The bacterial diversity in polluted soil remained intact throughout all radiation treatments. Phylogenetic analysis showed that members belonging to three taxonomic groups, alphaproteobacteria, gammaproteobacteria and actinobacteria were present in hydrocarbon polluted soil that were not affected by all radiation treatments. Gamma irradiation had a greater effect on bacterial community in both garden and uncultivated clay soils.
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