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Abstract
Amany Abd El Hameed: Removal of some toxic heavy metals contaminants from Egyptian phosphatic fertilizers using microorganisms. Unpublished M.Sc. Thesis, Department of Agric. Microbiology. Faculty of Agriculture, Ain shams University, 2016.
A number of 50 microbial isolates were isolated from 3 representative samples (monophosphate fertilizer, tri-phosphate fertilizer and rock phosphate). The highest number and percentage of isolates were obtained from tri-phosphate fertilizer followed by rock phosphate then monophosphate fertilizer samples. Theses isolates were tested for biosorption of heavy metal on solid medium supplemented with different metal ions at 50 ppm. Thirty microbial isolates (12 bacterial and 18 fungal isolates) out of 50 isolates were able to grow on solid medium containing heavy metal. The selected isolates were also screened for removal heavy metal with different concentrations (0- 150 ppm) in liquid medium. Among these 30 isolates, 11 isolates (6 fungal isolates and 5 bacterial isolates) were chosen for their high capability to tolerance high concentration of heavy metals (150 ppm). Only 5 isolates (BR5 & BR12 bacterial isolates and FR1, FR11 and FR13 fungal isolates) were selected as high ability to remove heavy metals. The identification of the most effective two bacterial isolates BR5 and BR12 and three fungal isolates FR1, FR11 and FR13 were carried out using phenotype. Some nutritional factors (carbon and nitrogen sources) affecting heavy metal removal by selected isolates were investigated. Glucose and lactose were the best carbon sources and tryptone or yeast extract were the best nitrogen sources for selected bacterial or fungal isolates, respectively. Evaluation of 7 factors, culture conditions (pH, temperature, inoculums size, incubation period and agitation speed) and medium constitution (carbon source concentration and nitrogen source concentration) affecting heavy metal removal by the most efficient isolates Bacillus sp. BR12 and Aspergillus sp. FR1 was investigated using the Placket-Burman statistical experimental design. The most positive significant variables affecting heavy metals
biosorption by Bacillus sp. BR12 being tryptone, temperature, agitation, inoculum size & incubation period in presence Cr+5 and glucose, pH & temperature in presence Rock phosphate and Aspergillus sp. FR1 being yeast extract, temperature, & inoculum size in presence Cr+5 and lactose, yeast extract, temperature & incubation period in presence Cu+2 were further optimized by using Response Surface Methodology (RSM) based central composite design (CCD). By using the surface plots and response optimizer of statistical software package Design-Expert software 9.0.0 (Stat-Ease, Inc., Minneapolis, MN 55413, USA 2014). the maximum growth of Bacillus sp. BR12 in presence of RP being 3.39 gl-1 was predicted when glucose was 1.5 and adjusted pH 7 then incubated at 25°C and maximum growth in presence of Cr+2 was predicted being 4.22 gl-1, corresponding 0.8 % tryptone, an incubation temperature of 35°C, 100 rpm of agitation speed, 5% inoculum size and 32h incubation period. Whereas the highest growth of Aspergillus sp FR1 in presence of Cr+5 and Cu+2 (4.31 gl-1 and 3.69 gl-1) were attained at 0.15% yeast extract and inoculated with 2% inoculum size then incubated at 28°C and 0.65 % lactose, 0.15% yeast extract, an incubation temperature of 30 °C and 8 days incubation period, respectively. The most efficient heavy metal resistant isolates (Bacillus sp. BR12 and Aspergillus sp. FR1) were identified using 16 and 18SrRNA gene sequencing. The strain of Bacillus sp. BR12 was close to the gene sequencing of Bacillus eiseniae strain. While Aspergillus sp. FR1 was close to the gene sequencing of Aspergillus terreus strain. There are no difference signification between absorption and adsorption mechanism for reduction heavy metals from samples. So, both strains dependent on absorption mechanism.
Keywords: Aspergillus, Bacillus, Biosorption, Heavy metals, Phosphatic fertilizers, Pseudomonas, Response surface methodology