Characterization of a molybdenum-reducing bacterium with the ability to degrade phenol, isolated in soils from Egypt

Polluted sites often contain both heavy metals and organic xenobiotic contaminants. This warrants the use of either a great number of bacterial degraders or bacteria having the ability to detoxify several toxicants simultaneously. In this research, the ability of a molybdenum-reducing (Mo-reducing) bacterium isolated from contaminated soil to decolorize various phenolics independent of Mo reduction was screened. Studies showed that this bacterium was able to grow on 4-nonylphenol and reduced molybdate to M0-blue. The optimal condition for this activity was pH between 6.3 and 6.8 and temperature of 34°C. Glucose proved to be the best electron donor for supporting molybdate reduction followed by galactose, fructose, and citrate in descending order. Other requirements included a phosphate concentration between 2.5 mM and 7.5 mM and a molybdate concentration between 20 and 30 mM. The absorption spectrum of the Mo-blue produced was similar to numerous previously described Mo-reducing bacteria, closely resembling a spectrum of the reduced phosphomolybdate. Mo reduction was inhibited by mercury (II), silver (I), copper (II), cadmium (II), and chromium (VI) at 2 ppm by 79.6%, 64.2%, 51.3%, 28.1%, and 25.0%, respectively. The biochemical analysis resulted in a tentative identification of the bacterium as Pseudo- monas aeruginosa strain Amr-11. The ability of this bacterium to detoxify Mo and grow on nonylphenol makes this bacterium an important tool for bioremediation.