THE MICROBIOLOGY AND BIOGEOCHEMISTRY OF DESERT SOILS NOTABLY IN RELATION TO MICROBIAL PHOSPHATE SOLUBULIZATION

The aim of the work reported in this Thesis was to investigate the role of a range of microorganisms in the functioning of the desert environment, particularly in relation to the biogeochemical cycles. A study was made of the microbial activity of phosphate soils in comparison with that found in a fertile, temperate grassland soil. The microbial transformations studied included phosphate solubilization, the oxidation of elemental sulphur to sulphate, nitrification and the hydrolysis of urea by microbes and were collectively used to study the biogeochemical activity of soils. Bacterial and fungal population densities in the soils, temperate grassland, and phosphate mine spoil desert-vegetated soil samples were investigated. In all cases the highest activity of the individual components of the mineral cycles was not surprisingly, found in the temperate grassland (control soil). The highest activities in the desert soils were associated with vegetation cover, i.e. the establishment of a rhizosphere. A variety of bacteria and fungi were isolated from phosphate mine spoil desert-vegetated soil and desert non-vegetated soil samples were identified using molecular identification techniques based on DNA extraction, PCR amplification and determination of the sequences 16SrRNA and 18SrRNA genes. The isolates were: bacteria- Paracoccus sp., Rhizobium sp, Bacillus megaterium, Cupriavidus necator, Bacillus simplex and Bacillus foraminis and fungi Cochliobolus lunatus, Penicillium daleae, Mucor sp. and Aspergilus oryzae. The following desert soil fungi, solubilized insoluble phosphate: Cochliobolus lumans, Penicillium daleae and Mucor Sp. Using NMR it was shown that soluble phosphate was released into the medium and also taken up by the fungi and fixed as metal phosphates.