Hesham Abdulla

COMPARATIVE STUDIES OF MICROBIAL COMMUNITIES ON STONE MONUMENTS IN TEMPERATE AND SEMI-ARID CLIMATES

Climate is recognised to play an important part in influencing the activity of microorganisms on stone in monuments and other objects of cultural value. In the UK and Greece, the numbers and distribution of heterotrophic bacteria were not strongly related to seasonal changes in temperature and rainfall. At Portchester Castle, qualitative changes in bacterial populations have been observed; actinomycetes were found only on decayed stone and dominant on stone from Tell Basta, in semi-arid Egypt. In the Minoan Palace at Petras and the fortifications of Khania, higher counts of halotolerant heterotrophic bacteria were found in sheltered areas on stone showing other biological growths and salt efflorescence. For all monuments, stones of lower mechanical strength supported higher bacterial counts and electron microscopy showed extensive sheets of biofilm. Estimations of carbohydrate in stone could also be related to whether the sites were exposed or protected. There is evidence to suggest that variations in the nature of bacterial populations may be dependent on season in temperate regions and in the Mediterranean climate related to the location within the monument. Biofilm production and perhaps halotolerance provide means by which bacteria resist adverse changes in moisture levels. Extreme fluctuations in moisture may induce major shifts in bacterial populations selecting filamentous, spore-forming types that penetrate deeper into the stone.

Bioleaching of Uranium From Egyptian Rocks Using Native Actinomycete Strains

ABSTRACT Bioleaching is an economic, novel practice for extraction of metals from their sources by microorganisms. The current study aimed to extract uranium from Egyptian ores using native strains of actinomycetes. Two types of rocks and one ore sample were collected from west-central Sinai, Egypt. Major oxides of the samples and fourteen heavy metals, including uranium, were determined. X-ray diffraction analysis proved that uranium was present in the samples in various structures. Uranium was present in different concentrations, 220, 770, and 550 mg/kg in sandstone, granite, and manganese ore, respectively. Thirty-four actinomycete isolates were recovered from the studied samples using four different isolation media. Acid production capabilities were employed to select isolates for further leaching experiments. Bioleaching experiments were carried out using sterile and non-sterile ore samples. Using sterile ore samples, the highest solubilization percentages of U3O8 were 44.5, 38.55, and 16.76% from sandstone, manganese ore, and granite sample, achieved by isolates UA12, UA5, and U7, respectively. Lower solubilization percentages of U3O8 were recorded by using non-sterile ore samples. Investigating the factors affecting the bioleaching abilities of the tested organisms revealed that 10 days of incubation with 4% pulp density were the best conditions for U3O8 solubilization. The most efficient isolates were identified using 16S rRNA gene sequence analysis. UA12 identified to be Streptomyces bacillaris, while UA5 could not be identified, and U7 was assigned as uncultured bacterium clone. Scanning electron microscope examination of the bioleaching experiment showed different growth intensity within the active isolates. For larger-scale extraction purposes, a kilogram of sandstone, containing 220 mg of U3O8, was used in the form of a truncated cone in a heap leaching experiment. After 20 cycles, 14.72 mg/l (6.7%) of U3O8 was leached by S. bacillaris, while 19.36 mg/l (8.8%) of U3O8 was leached by chemical leaching using sulfuric acid. The results of this study prove that the extraction of uranium using actinomycetes could be exploited as less polluting, more economical, and more effective than traditional chemical extraction especially from low-grade ores or mining wastes.