Soil bacteria with the combined potential for oil utilization, nitrogen fixation, and mercury resistance

Pristine and oil-polluted coastal and desert soil samples from Kuwait contained between about 1.0 × 107 and 2.5 × 108 colony-forming units (CFU) g−1 of bacteria with the combined potential for hydrocarbon utilization, nitrogen fixation, and Hg2+ resistance and volatilization. Soils with a long history of oil pollution were richest in these bacteria, and contained strains with the highest resistance to mercury. In the presence of oil, mercury resistance by the studied predominant strains decreased, but strains from oily desert soils could still resist up to 80 ppm HgCl2 in the presence of oil. The oil-attenuation potential of predominant strains in culture was also inhibited by HgCl2. However, satisfactory oil-attenuation rates still occurred in culture in the presence of up to 400 ppm of HgCl2. The diazotrophic potential of these bacteria makes them self-sufficient, as far as their nitrogen nutrition is concerned. These findings highlight the role of these bacterial consortia in self-cleaning and bioremediation of environments contaminated with oil and mercury.