Application of single- and multiphasic michaelis-menten kinetics to predictive modeling for aquatic ecosystems

Abstract

The transport, fate and effects of many toxic chemicals in aquatic ecosystems are largely mediated by microbial transformations. In our research, we have assumed that the transformations are a result of enzymatic reactions, and thus follow Michaelis‐Menten kinetics. Using diverse field‐collected and laboratory microcosm microbiota, we obtained sufficient experimental data to reach some general conclusions concerning the strengths and weaknesses of using Michaelis‐Menten kinetics in making environmental predictions. We concluded that this approach is best suited to predicting microbial transformations for pollutant concentrations of approximately 10−7 M or lower. The approach also is applicable to high pollutant concentrations (saturated systems), provided that toxic effects of the pollutant and adaptation are considered. Unfortunately, most experiments have been conducted in the upper 10−7 to 10−4 M pollutant concentration range, which may approach saturation for a portion of enzymatic systems in a mixed population. This range is ideal for analytical purposes, but could be confounded by mixed‐order and multiphasic kinetics, toxic effects of the pollutant and adaptation. Adaptation, mass‐transport effects, multiphasic kinetics of pollutant uptake and transformation, and suppression of transformation by diauxie, biologically produced inhibitors, and other xenobiotic chemicals are some of the factors that we believe need to be more thoroughly evaluated to improve predictive modeling capabilities.

Growth Kinetics of Suspended Microbial Cells: From Single-Substrate-Controlled Growth to Mixed-Substrate Kinetics

“…To date, the discussion of whether intrinsic or extant kinetic parameters are better suited to describe the biodegradation processes and to predict the fate of organic compounds in nature and engineered systems is still under way (86,180). Unfortunately, most of the kinetic data reported in literature were determined somewhere between the two well-defined kinetic properties discussed above (150). Such data must therefore be interpreted with caution.…”

Kinetics of mineralization of phenols in lake water

“…A number of kinetic models have been developed or applied to characterize biodegradation in natural environments (7,10,25). Recently, however, a number of new models have been formulated to characterize the kinetics of biodegradation by pure cultures of bacteria, and statistical means have been proposed for evaluating the fits of these models to data obtained in studies of microbial processes (12,18).…”

Multiphasic Kinetics for Transformation of Methyl Parathion by Flavobacterium Species

“…As part of an effort to determine maximum safe levels of toxic chemicals in natural aquatic systems, the U.S. Environmental Protection Agency is developing and testing mathematical models for predicting the transport and fate of pollutants. For chemicals transformed or degraded via microbial processes, models typically employ rate coefficients based on Michaelis-Menten kinetics for substrate-enzyme reactions (8,10). More specifically, current models incorporate the assumption that a single set of kinetic constants, including a half-saturation (Km) value and a maximum velocity (V) value, governs reaction rates for a particular pollutant.…”