EFFECTS OF MEDIUM AND TRACE-METALS ON KINETICS OF CARBON-TETRACHLORIDE TRANSFORMATION BY PSEUDOMONAS SP STRAIN-KC

Under denitrifying conditions, Pseudomonas sp. strain KC transforms ca rbon tetrachloride (CT) to carbon dioxide via a complex but as yet und etermined mechanism. Transformation rates were first order with respec t to CT concentration over the CT concentration range examined (0 to 1 00 mug/liter) and proportional to protein concentration, giving pseudo -second-order kinetics overall. Addition of ferric iron (1 to 20 muM) to an actively transforming culture inhibited CT transformation, and t he degree of inhibition increased with increasing iron concentration. By removing iron from the trace metals solution or by removing iron-co ntaining precipitate from the growth medium, higher second-order rate coefficients were obtained. Copper also plays a role in CT transformat ion. Copper was toxic at neutral pH. By adjusting the medium pH to 8.2 , soluble iron and copper levels decreased as a precipitate formed, an d CT transformation rates increased. However, cultures grown at high p H without any added trace copper (1 muM) exhibited slower growth rates and greatly reduced rates of CT transformation, indicating that coppe r is required for CT transformation. The use of pH adjustment to decre ase iron solubility, to avoid copper toxicity, and to provide a select ive advantage for strain KC was evaluated by using soil slurries and g roundwater containing high levels of iron. In samples adjusted to pH 8 .2 and inoculated with strain KC, CT disappeared rapidly in the absenc e or presence of acetate or nitrate supplements. CT did not disappear in pH-adjusted controls that were not inoculated with strain KC.