Regeneration of Oxidative Assimilation Capacity by Intracellular Conversion of Storage Products to Protein

Previous studies have shown that the capacity of a heterogeneous microbial population for oxidative assimilation of glucose can be renewed by periodically subjecting the sludge (or a portion of it) to endogenous respiration in the presence of an exogenous source of nitrogen. Further study of this system led to a modification of the activated sludge process for nitrogen-deficient wastes. However, it was not known whether renewal of oxidative assimilation capacity was possible for substrates which required the presence of inducible enzyme(s) or for substrates which were not carbohydrates. Therefore, studies with lactose and acetate as carbon sources were designed. Both carbon sources were removed under conditions of oxidative assimilation, and the storage products (or a portion of these products) were converted into protein when the sludge was subjected to a period of endogenous respiration (with respect to carbon source) in the presence of an exogenous supply of ammonium sulfate. The “regenerated” sludge exhibited a renewed capacity for oxidative assimilation, thereby indicating that requisite inducible enzymes (e.g., β-galactosidase in the case of lactose; iso-citritase and malate synthetase in the case of acetate) were not diluted out in the endogenous phase to a degree sufficient to hamper renewed oxidative assimilation capacity. The results also indicated that a noncarbohydrate carbon source can be successfully removed from the medium with this process. However, in the case of acetate, the oxidative assimilation capacity after “regeneration” was not fully restored to the initial level.