A tritium (3H2)-oxidizing soil isolate was identified as Alcaligenes paradoxus, a gram-negative, rod-shaped bacterium. This organism belongs to a group of facultative autotrophs referred to as the 'hydrogen bacteria' due to their unique ability to utilize hydrogen as a sole source of energy for chemolithotrophic growth. Experiments with washed cells of A. paradoxus suspended in 0.025M potassium phosphate buffer (resting cells) showed that 1.0 ppm mercury (as Hg(NO3)2) caused a 95 percent reduction in hydrogen oxidation, whereas, concentration of 0.1 ppm and lower showed no inhibitory effects. When suspensions of A. paradoxus were added to sterile soil and then amended with mercury at concentrations of 1.0, 10.0, and 100.0 ppm, hydrogen oxidation was reduced 80 percent, 85 percent, and 95 percent, respectively, compared to soil controls with no mercury added. This showed that soil afforded, at least temporarily, some protection from toxic mercury effects. When cadmium or lead was used in solution, it was found that up to 100.0 ppm of these metals produced no detectable inhibition in the rate or extent of the hydrogen oxidation reaction at either pH 7.0 or 5.0. However, pretreatment of A. paradoxus cells with a combination of ethylenediaminetetraacetate (EDTA) and tris-(hydroxymethyl)-aminomethane (Tris), at a pH of 8.0, resulted in a reduction in oxidation in solutions containing 10.0 ppm of cadmium or lead, with the greater reduction being due to cadmium.

Monitoring Systems Research and Development Division, Environmental Monitoring and Support Laboratory. April 1979. Includes bibliographical references (pages 28-32).