STUDIES ON THE ENVIRONMENTAL MICROBIOLOGY AND BIOGEOCHEMISTRY OF DESERT SURFACE SOILS

Microorganisms play a key role in the functioning of the environment, particularly in relation to the biogeochemical cycles. Here, a study was made of the microbial activity of primitive desert surface soils in comparison with that exhibited by a fertile agricultural loam soil. The microbial transformations studied included nitrification, the hydrolysis of urea, the oxidation of elemental sulphur to sulphate and phosphate solubilisation; these processes were collectively used to study the biogeochemical activity of desert surface soils. Bacterial population densities in the desert surface soils, fertile loam soils and volcanic, cave rock samples were also determined. A variety of bacterial isolates from desert surface soils and cave rock samples have been identified using molecular identification techniques like DNA extraction, PCR amplification, determinations of 16S and 18S rRNA gene sequences. The isolation and characterization of extremophilic bacterial strains from a dormant volcano on the island of Reunion is reported, using molecular identification, morphological and physiological studies. As the area of the volcano, from which these bacteria were isolated, has not been recently active, it was considered of interest to determine if these bacteria grow, or merely survive, in a mesophilic environment. Nuclear magnetic resonance spectroscopy (NMR) was used to study the compatible solutes in these isolates when growing under high temperatures, low and high pH stresses and at various concentrations of NaCl. Finally, various environmental samples were tested in order to detect the presence of Mycoplasma using an EZ-PCR Mycoplasma Test Kit.