The removal of radionuclide and toxic heavy metals from aqueous solutions, especially from contaminated sources, seems to be a significantly useful subject for environmental control and human health. In this regard, the biosorption of several heavy metals from the aqueous solution using various microorganisms has been investigated. Among the microorganisms tested, high uranium absorption ability was exhibited by certain gram-positive bacterial strains, notably Arthrobacter nicotianae IAM12342, Bacillus subtilis IAM1026, and Micrococcus luteus IAM1056 at pH 5.8. A. nicotianae cells which showed the best performance, could adsorb 698 mg uranyl ion (2.58 mmol) per gram dry wt. microorganism cells in 1 h. The amount of uranium absorbed by A. nicotianae cells was increased with increasing pH of the solution below pH 5. On the other hand, zeta-potential of the surface of A. nicotianae cells was decreased with increasing pH of the solution below pH 5. The dominant chemical species of uranium is UO₂²⁺ below pH 4. Thus, the bond between positively charged uranyl ion and negatively charged A. nicotianae cells was increased with increasing pH of the solution below pH 5. Generally, the negative charge of gram-positive bacteria depends of the amount of phosphate groups in the teichoic acid polymers of the surface of the cells. The molar ratio of negatively charged H₂PO₄^- increased with increasing pH of the solution below pH 4.5. Additionally, the biosorption of gold using various microorganisms were also examined. The amounts of absorbed gold by the most of gram-negative bacteria were higher than those by the most of gram-positive bacteria. The effect of pH on the amount of absorbed gold and the Zeta-potential of the surface of Pseudomonas maltophilia cells, which absorbed the highest amount of gold, will be also discussed.