LOW CHEMICAL CONCENTRATION AND pH AS FACTORS LIMITING THE SUCCESS OF INOCULATION TO ENHANCE BIODEGRADATION

Abstract

A strain of Pseudomonas that mineralized 1 microgram of p-nitrophenol (PNP) per milliliter in culture failed to mineralize the compound in nonsterile or sterile lake water. The bacterium did not act on PNP at the pH of the lake water (pH 8.0) or in culture medium at the same pH, although it did mineralize PNP when added to sterile lake water samples adjusted to pH 7.0. A second strain of Pseudomonas that grew and mineralized 1 μg PNP/ml in culture at pH 8.0 and in sterile lake water at pH 7.0 neither mineralized nor grew on PNP in sterile lake water at pH 8.0. A third strain of Pseudomonas grew on and mineralized 1 μg PNP/ml in sterile lake water at pH 8.0 but failed to enhance mineralization when added to nonsterile lake water at that pH. Corynebacterium sp. grew on and mineralized 1 μg PNP/ml in culture medium and in sterile lake water, and its inoculation into nonsterile lake water greatly reduced the time for the mineralization of 1.0 and 0.1 μg PNP/ml. The inoculation of nonsterile lake water with Corynebacterium sp., which mineralized 26 and 17 ng PNP/ml in culture, resulted in a biphasic transformation of 26 and 16 ng PNP/ml. Only the initial phase was more rapid than in uninoculated lake water. Inoculation of Corynebacterium sp. into sewage markedly shortened the time for extensive mineralization of 100 ng but not of 26 and 16 ng PNP/ml. We suggest that microorganisms that are able to degrade chemicals in culture may not do so when introduced into natural environments because of unfavorable pH or the organisms' inability to readily use compounds that are present at low concentrations.