Supplemental Carbon Use by Microorganisms Degrading Toxic Organic Compounds and the Concept of Specific Toxicity

Abstract

ABSTRACT

Biological treatment can be used to decontaminate soil and water polluted by toxic organic compounds. Some compounds are metabolized too slowly under natural conditions to be effectively removed from the contaminated system. The technical literature contains several examples where nutrient manipulation has been used to enhance microbial metabolism. One promising technique for increasing absolute biodegradation rates of organic toxins is to augment microbial biomass by adding a supplemental carbon substrate. Simultaneous metabolism of the toxic and supplemental substrates requires maintenance of growth limiting carbon concentrations in culture to avoid catabolite repression. Populations of microorganisms can metabolize very low levels of organic toxins at accelerated rates when an ancillary carbon source is supplied. Cell-specific degradation rates may remain unchanged, but absolute removal rates are increased by virtue of increased biomass. Ancillary carbon can also stabilize a population of microorganisms in the presence of high and otherwise inhibitory concentrations of organic toxins. In such cases where organic toxin levels are high and biomass is augmented by supplemental carbon a measure of toxicity is required which accounts for microbial population density as well as toxin concentration. This second order parameter is called specific toxicity.