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Authors: Muhammad Rafique, Hafiz
Keywords: Applied Sciences
Agriculture & related technologies
Issue Date: 2015
Abstract: Petroleum, the backbone of today's mechanized society, now became a threat to environment due to extraction and transportation. Due to transportation accidental spills occur regularly all over the world. Such spills have also occurred at many locations throughout Pakistan over time. Petroleum and its products contain carcinogenic and mutagenic compounds and therefore contamination of soil from petroleum hydrocarbons is a serious problem. Efforts are now focused on seeking potential remediation techniques for cleanup of petroleum contaminated soils in a cost effective and eco-friendly way. Plant assisted bioremediation of petroleum contaminated soil is getting attention as compared to the alone use of either microorganism or plant. The challenging task for such efforts to be successful is not only the survival of microorganisms upon their inoculation into xenobiotic environment but also microbe’s positives interaction with plants. Plant growth promoting bacteria (PGPB) having 1-aminocyclopropane 1-carboxylic acid deaminase (ACC-deaminase) are considered to helpful for plants in stressed environment by reducing stress induced ethylene. Over three hundred bacterial isolates were cultured from collected petroleum contaminated soil samples. Bioremediation and ACCmetabolism assays screened out 27 from 301 bacterial isolates. These 27 bacterial isolates possessed medium to high bioremediation potential for PAHs and also high ACC deaminase activity. Compatibility of these 27 bacterial isolates with alfalfa, maize and canola was assayed in growth pouches and jar experiment under axenic conditions. Finally, on the basis of bioremediation, ACC-deaminase and plant growth promotion activity, 8 bacterial isolates were screened out. Plant -assisted bioremediation of artificially spiked coarse textured soil bearing 10,000 mg kg-1 (w/w) crude oil concentration was carried out both under controlled and ambient conditions of light and temperature. Also growth performance of inoculated plants was compared with uninoculated plants for each crop. After 60 days, results revealed that four bacterial isolates Bacillus subtilis, Bacillus cereus and other Bacillus sp. significantly degraded petroleum hydrocarbons. The most efficient was Bacillus subtilis which reduced TPH contamination 47%, 37% and 43% in combination with alfalfa, canola and maize, respectively. While the same bacterium when inoculated alone reduced 33% TPH contamination under controlled light and temperature while 31% under ambient light and temperature. Significant increase in growth attributes such as root length, shoot length and fresh biomass of all three crops was observed as compared to their corresponding un-inoculated plant control. Comparatively, alfalfa with respect to germination and growth in petroleum contaminated soil performed better as compared to maize and canola. Study can be concluded that use of bacteria possessed with dual traits of bioremediation potential and ACC-deaminase activity in combination with plant can be a good approach for remediation of petroleum hydrocarbons contaminated soil.
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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