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Appl Environ Microbiol. 1990 September; 56(9): 2692-2697
Copyright © 1990, American Society for Microbiology. All Rights Reserved.

Coexisting Bacterial Populations Responsible for Multiphasic Mineralization Kinetics in Soil

S. K. Schmidt^* and M. J. Gier

Department of Environmental, Population and Organismic Biology, University of Colorado, Boulder, Colorado 80309

ABSTRACT

Experiments were conducted to study populations of indigenous microorganisms capable of mineralizing 2,4-dinitrophenol (DNP) in two soils. Previous kinetic analyses indicated the presence of two coexisting populations of DNP-mineralizing microorganisms in a forest soil (soil 1). Studies in which eucaryotic and procaryotic inhibitors were added to this soil indicated that both populations were bacterial. Most-probable-number counts with media containing different concentrations of DNP indicated that more bacteria could mineralize low concentrations of DNP than could metabolize high concentrations of it. Enrichments with varying concentrations of DNP and various combinations of inhibitors consistently resulted in the isolation of the same two species of bacteria from soil 1. This soil contained a large number and variety of fungi, but no fungi capable of mineralizing DNP were isolated. The two bacterial isolates were identified as a Janthinobacterium sp. and a Rhodococcus sp. The Janthinobacterium sp. had a low µ_max and a low K_m for DNP mineralization, whereas the Rhodococcus sp. had much higher values for both parameters. These differences between the two species of bacteria were similar to differences seen when soil was incubated with different concentrations of DNP. Values for µ_max from soil incubations were similar to µ_max values obtained in pure culture studies. In contrast, K_s and K_m values showed greater variation between soil and pure culture studies. The results of this study help to confirm predictions that two physiologically distinct bacterial populations are responsible for the multiphasic mineralization kinetics observed in the soil studied.

^* Corresponding author.

Present address: Engineering-Science, Inc., Denver, CO 80204.

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