Nonlinear estimation of the parameters of Monod kinetics that best describe mineralization of several substrate concentrations by dissimilar bacterial densities.

The kinetics of mineralization of a wide range of concentrations of benzoate, glucose, and benzylamine by Pseudomonas sp., Salmonella typhimurium, and microorganisms in acclimated sewage was studied. The treatment of initial substrate concentration and population density as independent variables in nonlinear regression analysis permitted the estimation of a single value for each of the parameters of Monod kinetics that best described the mineralization of substrate at each concentration by the pure cultures and the sewage microflora. One value for each of the parameters of Monod kinetics was used for each of the three compounds to produce theoretical curves which lay close to the observed data on mineralization. Statistically significant differences existed in the values of the parameters of Monod kinetics that best described mineralization in cultures differing only in initial substrate concentration and cell density. However, for the compounds tested, the variance left by analyses using one value for each parameter of Monod kinetics was less than double the unexplained variance left by individual analyses of the data from each treatment. Although significant, this increase is small compared with the amount of variance that could be explained using only one value for each parameter of Monod kinetics.     

Nonlinear estimation of the parameters of Monod kinetics that best describe mineralization of several substrate concentrations by dissimilar bacterial densities

The kinetics of mineralization of a wide range of concentrations of benzoate, glucose, and benzylamine by Pseudomonas sp., Salmonella typhimurium, and microorganisms in acclimated sewage was studied. The treatment of initial substrate concentration and population density as independent variables in nonlinear regression analysis permitted the estimation of a single value for each of the parameters of Monod kinetics that best described the mineralization of substrate at each concentration by the pure cultures and the sewage microflora. One value for each of the parameters of Monod kinetics was used for each of the three compounds to produce theoretical curves which lay close to the observed data on mineralization. Statistically significant differences existed in the values of the parameters of Monod kinetics that best described mineralization in cultures differing only in initial substrate concentration and cell density. However, for the compounds tested, the variance left by analyses using one value for each parameter of Monod kinetics was less than double the unexplained variance left by individual analyses of the data from each treatment. Although significant, this increase is small compared with the amount of variance that could be explained using only one value for each parameter of Monod kinetics.     

Kinetics of mineralization of phenols in lake water.

The kinetics of mineralization of phenol and p-nitrophenol in lake water was determined at concentrations from 200 pg/ml to 5 micrograms/ml. The mineralization data were fit by nonlinear regression to equations for 14 kinetic models that describe patterns of biodegradation by nongrowing cells or by microorganisms growing on either the test chemical or other organic substrates. The kinetics od mineralization of phenol in water samples collected in July was best described by first-order models for 0.5 ng of phenol per ml; by Monod-without-growth, logistic, and logarithmic models for 1.0 and 2.0 ng/ml and 5.0 ng/ml to 1.0 micrograms/ml, respectively, if it is assumed that the mineralizing population uses phenol as the sole carbon source for growth; by models (for phenol at concentrations of 2.0 ng/ml to 1.0 micrograms/ml) that assume that the phenol-mineralizing populations do not grow or grow logarithmically or logistically on uncharacterized carbon compounds but metabolize the phenol when present at levels below and above Km, respectively, for that compound; and by a logarithmic model at 5.0 micrograms/ml. Under the test conditions, usually less than 10% of the phenol C that was metabolized was incorporated into microbial cells or retained by other particulate material in the water at substrate concentrations of 10 ng/ml or less, and the percentage increased at higher substrate concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetics of mineralization of phenols in lake water

The kinetics of mineralization of phenol and p-nitrophenol in lake water was determined at concentrations from 200 pg/ml to 5 micrograms/ml. The mineralization data were fit by nonlinear regression to equations for 14 kinetic models that describe patterns of biodegradation by nongrowing cells or by microorganisms growing on either the test chemical or other organic substrates. The kinetics od mineralization of phenol in water samples collected in July was best described by first-order models for 0.5 ng of phenol per ml; by Monod-without-growth, logistic, and logarithmic models for 1.0 and 2.0 ng/ml and 5.0 ng/ml to 1.0 micrograms/ml, respectively, if it is assumed that the mineralizing population uses phenol as the sole carbon source for growth; by models (for phenol at concentrations of 2.0 ng/ml to 1.0 micrograms/ml) that assume that the phenol-mineralizing populations do not grow or grow logarithmically or logistically on uncharacterized carbon compounds but metabolize the phenol when present at levels below and above Km, respectively, for that compound; and by a logarithmic model at 5.0 micrograms/ml. Under the test conditions, usually less than 10% of the phenol C that was metabolized was incorporated into microbial cells or retained by other particulate material in the water at substrate concentrations of 10 ng/ml or less, and the percentage increased at higher substrate concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetics of p-nitrophenol mineralization by a Pseudomonas sp.: effects of second substrates.

The kinetics of simultaneous mineralization of p-nitrophenol (PNP) and glucose by Pseudomonas sp. were evaluated by nonlinear regression analysis. Pseudomonas sp. did not mineralize PNP at a concentration of 10 ng/ml but metabolized it at concentrations of 50 ng/ml or higher. The Ks value for PNP mineralization by Pseudomonas sp. was 1.1 micrograms/ml, whereas the Ks values for phenol and glucose mineralization were 0.10 and 0.25 micrograms/ml, respectively. The addition of glucose to the media did not enable Pseudomonas sp. to mineralize 10 ng of PNP per ml but did enhance the degradation of higher concentrations of PNP. This enhanced degradation resulted from the simultaneous use of glucose and PNP and the increased rate of growth of Pseudomonas sp. on glucose. The Monod equation and a dual-substrate model fit these data equally well. The dual-substrate model was used to analyze the data because the theoretical assumptions of the Monod equation were not met. Phenol inhibited PNP mineralization and changed the kinetics of PNP mineralization so that the pattern appeared to reflect growth, when in fact growth was not occurring. Thus, the fitting of models to substrate depletion curves may lead to erroneous interpretations of data if the effects of second substrates on population dynamics are not considered.     

Kinetics of p-nitrophenol mineralization by a Pseudomonas sp.: effects of second substrates

The kinetics of simultaneous mineralization of p-nitrophenol (PNP) and glucose by Pseudomonas sp. were evaluated by nonlinear regression analysis. Pseudomonas sp. did not mineralize PNP at a concentration of 10 ng/ml but metabolized it at concentrations of 50 ng/ml or higher. The Ks value for PNP mineralization by Pseudomonas sp. was 1.1 micrograms/ml, whereas the Ks values for phenol and glucose mineralization were 0.10 and 0.25 micrograms/ml, respectively. The addition of glucose to the media did not enable Pseudomonas sp. to mineralize 10 ng of PNP per ml but did enhance the degradation of higher concentrations of PNP. This enhanced degradation resulted from the simultaneous use of glucose and PNP and the increased rate of growth of Pseudomonas sp. on glucose. The Monod equation and a dual-substrate model fit these data equally well. The dual-substrate model was used to analyze the data because the theoretical assumptions of the Monod equation were not met. Phenol inhibited PNP mineralization and changed the kinetics of PNP mineralization so that the pattern appeared to reflect growth, when in fact growth was not occurring. Thus, the fitting of models to substrate depletion curves may lead to erroneous interpretations of data if the effects of second substrates on population dynamics are not considered.     

Two approaches to modeling kinetics of biodegradation by growing cells and application of a two-compartment model for mineralization kinetics in sewage

The patterns of microbial mineralization of 0.3 to 30 ng of glucose, benzoate, and phenol per ml of sewage collected in late fall and winter were analyzed with the integrated Monod equation and a model in which growth of active organisms occurs at the expense of organic compounds other than the test substrate. Either model could be closely fit by nonlinear regression to the data from individual tests with one concentration of substrate added to one dilution of sewage. However, neither model accounted satisfactorily for differences in patterns of mineralization resulting from differences in substrate concentration and cell density between different tests. It is suggested that both the added substrates and other organics present in sewage contributed to the growth of the active organisms. The mineralization of glucose in sewage collected in summer was better described by a two-compartment model than by any other model tested.     

Two approaches to modeling kinetics of biodegradation by growing cells and application of a two-compartment model for mineralization kinetics in sewage.

The patterns of microbial mineralization of 0.3 to 30 ng of glucose, benzoate, and phenol per ml of sewage collected in late fall and winter were analyzed with the integrated Monod equation and a model in which growth of active organisms occurs at the expense of organic compounds other than the test substrate. Either model could be closely fit by nonlinear regression to the data from individual tests with one concentration of substrate added to one dilution of sewage. However, neither model accounted satisfactorily for differences in patterns of mineralization resulting from differences in substrate concentration and cell density between different tests. It is suggested that both the added substrates and other organics present in sewage contributed to the growth of the active organisms. The mineralization of glucose in sewage collected in summer was better described by a two-compartment model than by any other model tested.     

Kinetics of mineralization of organic compounds at low concentrations in soil.

The kinetics of mineralization of 14C-labeled phenol and aniline were measured at initial concentrations ranging from 0.32 to 5,000 ng and 0.30 ng to 500 micrograms/g of soil, respectively. Mineralization of phenol at concentrations less than or equal to 32 ng/g of soil and of aniline at all concentrations began immediately, and the curves for the evolution of labeled CO2 were biphasic. The patterns of mineralization of 4.0 ng of 2,4-dichlorophenol per g of soil and 20 ng of nitrilotriacetic acid per g of soil were similar to the patterns for phenol and aniline. The patterns of mineralization of 1.0 to 100 ng of p-nitrophenol and 6.0 ng of benzylamine per g of soil were also biphasic but after a short apparent lag period. The curves of CO2 evolution from higher concentrations of phenol and p-nitrophenol had increasing apparent lag phases and were S-shaped or linear. Cumulative plots of the percentage of substrate converted to CO2 were fit by nonlinear regression to first-order, integrated Monod, logistic, logarithmic, zero-order, three-half-order, and two-compartment models. None of the models of the Monod family provided the curve of best fit to any of the patterns of mineralization. The linear growth form of the three-half-order model provided the best fit for the mineralization of p-nitrophenol, with the exception of the lowest concentrations, and of benzylamine. The two-compartment model provided the best fit for the mineralization of concentrations of phenol below 100 ng/g, of several concentrations of aniline, and of nitrilotriacetic acid. It is concluded that models derived from the Monod equation, including the first-order model, do not adequately describe the kinetics of mineralization of low concentrations of chemicals added to soil.     

Kinetics of mineralization of organic compounds at low concentrations in soil

The kinetics of mineralization of 14C-labeled phenol and aniline were measured at initial concentrations ranging from 0.32 to 5,000 ng and 0.30 ng to 500 micrograms/g of soil, respectively. Mineralization of phenol at concentrations less than or equal to 32 ng/g of soil and of aniline at all concentrations began immediately, and the curves for the evolution of labeled CO2 were biphasic. The patterns of mineralization of 4.0 ng of 2,4-dichlorophenol per g of soil and 20 ng of nitrilotriacetic acid per g of soil were similar to the patterns for phenol and aniline. The patterns of mineralization of 1.0 to 100 ng of p-nitrophenol and 6.0 ng of benzylamine per g of soil were also biphasic but after a short apparent lag period. The curves of CO2 evolution from higher concentrations of phenol and p-nitrophenol had increasing apparent lag phases and were S-shaped or linear. Cumulative plots of the percentage of substrate converted to CO2 were fit by nonlinear regression to first-order, integrated Monod, logistic, logarithmic, zero-order, three-half-order, and two-compartment models. None of the models of the Monod family provided the curve of best fit to any of the patterns of mineralization. The linear growth form of the three-half-order model provided the best fit for the mineralization of p-nitrophenol, with the exception of the lowest concentrations, and of benzylamine. The two-compartment model provided the best fit for the mineralization of concentrations of phenol below 100 ng/g, of several concentrations of aniline, and of nitrilotriacetic acid. It is concluded that models derived from the Monod equation, including the first-order model, do not adequately describe the kinetics of mineralization of low concentrations of chemicals added to soil.     

Models for the kinetics of biodegradation of organic compounds not supporting growth

We developed 12 models of kinetics to describe the metabolism of organic substrates that are not supporting bacterial growth. These models can be used to describe the biodegradation of organic compounds that are not supporting growth when the responsible populations are growing logistically, logarithmically, or linearly or are not increasing in numbers. Nonlinear regression analysis was used to fit patterns of mineralization by two bacteria to these kinetic models. Pseudomonas acidovorans mineralized 1 ng of phenol per ml while growing exponentially at the expense of uncharacterized organic carbon in a synthetic medium. Phenol at a concentration of 1 ng/ml did not affect the growth of P. acidovorans. These data were best fit by the model that incorporates the equation for logarithmic growth and assumes a concentration of test substrate well below its Km value. In the absence of a second substrate, glucose at concentrations below those supporting growth was mineralized by Salmonella typhimurium in a manner best described by pseudo first-order kinetics. In the presence of different concentrations of arabinose, however, the kinetics of glucose mineralization by S. typhimurium reflected linear, logistic, or logarithmic growth of the population on arabinose. We conclude that the kinetics of mineralization of organic compounds at concentrations too low to support growth are best described either by the first-order model or by models that incorporate expressions for the kinetics of growth of the metabolizing population on other substrates. When growth is at the expense of other substrates, the kinetics observed reflect such growth, as well as the concentration of the substrate of interest.(ABSTRACT TRUNCATED AT 250 WORDS)     

Models for the kinetics of biodegradation of organic compounds not supporting growth.

We developed 12 models of kinetics to describe the metabolism of organic substrates that are not supporting bacterial growth. These models can be used to describe the biodegradation of organic compounds that are not supporting growth when the responsible populations are growing logistically, logarithmically, or linearly or are not increasing in numbers. Nonlinear regression analysis was used to fit patterns of mineralization by two bacteria to these kinetic models. Pseudomonas acidovorans mineralized 1 ng of phenol per ml while growing exponentially at the expense of uncharacterized organic carbon in a synthetic medium. Phenol at a concentration of 1 ng/ml did not affect the growth of P. acidovorans. These data were best fit by the model that incorporates the equation for logarithmic growth and assumes a concentration of test substrate well below its Km value. In the absence of a second substrate, glucose at concentrations below those supporting growth was mineralized by Salmonella typhimurium in a manner best described by pseudo first-order kinetics. In the presence of different concentrations of arabinose, however, the kinetics of glucose mineralization by S. typhimurium reflected linear, logistic, or logarithmic growth of the population on arabinose. We conclude that the kinetics of mineralization of organic compounds at concentrations too low to support growth are best described either by the first-order model or by models that incorporate expressions for the kinetics of growth of the metabolizing population on other substrates. When growth is at the expense of other substrates, the kinetics observed reflect such growth, as well as the concentration of the substrate of interest.(ABSTRACT TRUNCATED AT 250 WORDS)     

Explanations for the acclimation period preceding the mineralization of organic chemicals in aquatic environments

A study was conducted of possible reasons for acclimation of microbial communities to the mineralization of organic compounds in lake water and sewage. The acclimation period for the mineralization of 2 ng of p-nitrophenol (PNP) or 2,4-dichlorophenoxyacetic acid per ml of sewage was eliminated when the sewage was incubated for 9 or 16 days, respectively, with no added substrate. The acclimation period for the mineralization of 2 ng but not 200 ng or 2 micrograms of PNP per ml was eliminated when the compound was added to lake water that had been first incubated in the laboratory. Mineralization of PNP by Flavobacterium sp. was detected within 7 h at concentrations of 20 ng/ml to 2 micrograms/ml but only after 25 h at 2 ng/ml. PNP-utilizing organisms began to multiply logarithmically after 1 day in lake water amended with 2 micrograms of PNP per ml, but substrate disappearance was only detected at 8 days, at which time the numbers were approaching 10(5) cells per ml. The addition of inorganic nutrients reduced the length of the acclimation period from 6 to 3 days in sewage and from 6 days to 1 day in lake water. The prior degradation of natural organic materials in the sewage and lake water had no effect on the acclimation period for the mineralization of PNP, and naturally occurring inhibitors that might delay the mineralization were not present. The length of the acclimation phase for the mineralization of 2 ng of PNP per ml was shortened when the protozoa in sewage were suppressed by eucaryotic inhibitors, but it was unaffected or increased if the inhibitors were added to lake water.(ABSTRACT TRUNCATED AT 250 WORDS)     

Explanations for the acclimation period preceding the mineralization of organic chemicals in aquatic environments.

A study was conducted of possible reasons for acclimation of microbial communities to the mineralization of organic compounds in lake water and sewage. The acclimation period for the mineralization of 2 ng of p-nitrophenol (PNP) or 2,4-dichlorophenoxyacetic acid per ml of sewage was eliminated when the sewage was incubated for 9 or 16 days, respectively, with no added substrate. The acclimation period for the mineralization of 2 ng but not 200 ng or 2 micrograms of PNP per ml was eliminated when the compound was added to lake water that had been first incubated in the laboratory. Mineralization of PNP by Flavobacterium sp. was detected within 7 h at concentrations of 20 ng/ml to 2 micrograms/ml but only after 25 h at 2 ng/ml. PNP-utilizing organisms began to multiply logarithmically after 1 day in lake water amended with 2 micrograms of PNP per ml, but substrate disappearance was only detected at 8 days, at which time the numbers were approaching 10(5) cells per ml. The addition of inorganic nutrients reduced the length of the acclimation period from 6 to 3 days in sewage and from 6 days to 1 day in lake water. The prior degradation of natural organic materials in the sewage and lake water had no effect on the acclimation period for the mineralization of PNP, and naturally occurring inhibitors that might delay the mineralization were not present. The length of the acclimation phase for the mineralization of 2 ng of PNP per ml was shortened when the protozoa in sewage were suppressed by eucaryotic inhibitors, but it was unaffected or increased if the inhibitors were added to lake water.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetics and Extent of Mineralization of Organic Chemicals at Trace Levels in Freshwater and Sewage

A sensitive and rapid method was developed to measure the mineralization of ¹⁴C-labeled organic compounds at picogram-per-milliliter or lower levels in samples of natural waters and sewage. Mineralization was considered to be equivalent to the loss of radioactivity from solutions. From 93 to 98% of benzoate, benzylamine, aniline, phenol, and 2,4-dichlorophenoxyacetate at one or more concentrations below 300 ng/ml was mineralized in samples of lake waters and sewage, indicating little or no incorporation of carbon into microbial cells. Assimilation of ¹⁴C by the cells mineralizing benzylamine in lake water was not detected. Mineralization in lake waters was linear with time for aniline at 5.7 pg to 500 ng/ml, benzylamine at 310 ng/ml, phenol at 102 fg to 10 mg/ml, 2,4-dichlorophenoxyacetate at 1.5 pg/ml, and di-(2-ethylhexyl) phthalate at 21 pg to 200 ng/ml, but it was exponential at several p-nitrophenol concentrations. The rate of mineralization of 50 and 500 ng of aniline per ml and 200 pg and 2.0 ng of the phthalate per ml increased with time in lake waters. The phthalate and 2,4-dichlorophenoxyacetate were mineralized in samples from a eutrophic but not an oligotrophic lake. Addition to eutrophic lake water of a benzoate-utilizing bacterium did not increase the rate of benzoate mineralization at 34 and 350 pg/ml but did so at 5 and 50 ng/ml. Glucose and phenol reduced the percentage of p-nitrophenol mineralized at p-nitrophenol concentrations of 200 ng/ml but not at 22.6 pg/ml and inhibited the rates of mineralization at both concentrations. These results show that the kinetics of mineralization, the capacity of the aquatic community to assimilate carbon from the substrate or the extent of assimilation, and the sensitivity of the mineralizing populations to organic compounds are different at trace levels than at higher concentrations of organic compounds.     

Reasons for possible failure of inoculation to enhance biodegradation

Pseudomonas strains capable of mineralizing 2,4-dichlorophenol (DCP) and p-nitrophenol (PNP) in culture media were isolated from soil. One DCP-metabolizing strain mineralized 1.0 and 10 micrograms of DCP but not 2.0 to 300 ng/ml in culture. When added to lake water containing 10 micrograms of DCP per ml, the bacterium did not mineralize the compound, and only after 6 days did it cause the degradation of 1.0 microgram of DCP per ml. The organism did not grow or metabolize DCP when inoculated into sterile lake water, but it multiplied in sterile lake water amended with glucose or with DCP and supplemental nutrients. Its population density declined and DCP was not mineralized when the pseudomonad was added to nonsterile sewage, but the bacterium grew in sterile DCP-amended sewage, although not causing appreciable mineralization of the test compound. Addition of the bacterium to nonsterile soil did not result in the mineralization of 10 micrograms of DCP per g, although mineralization was evident if the inoculum was added to sterile soil. A second DCP-utilizing pseudomonad failed to mineralize DCP when added to the surface of sterile soil, although activity was evident if the inoculum was mixed with the soil. A pseudomonad able to mineralize 5.0 micrograms of PNP per ml in culture did not mineralize the compound in sterile or nonsterile lake water. The bacterium destroyed PNP in sterile sewage and enhanced PNP mineralization in nonsterile sewage. When added to the surface of sterile soil, the bacterium mineralized little of the PNP present at 5.0 micrograms/g, but it was active if mixed well with the sterile soil.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reasons for possible failure of inoculation to enhance biodegradation.

Pseudomonas strains capable of mineralizing 2,4-dichlorophenol (DCP) and p-nitrophenol (PNP) in culture media were isolated from soil. One DCP-metabolizing strain mineralized 1.0 and 10 micrograms of DCP but not 2.0 to 300 ng/ml in culture. When added to lake water containing 10 micrograms of DCP per ml, the bacterium did not mineralize the compound, and only after 6 days did it cause the degradation of 1.0 microgram of DCP per ml. The organism did not grow or metabolize DCP when inoculated into sterile lake water, but it multiplied in sterile lake water amended with glucose or with DCP and supplemental nutrients. Its population density declined and DCP was not mineralized when the pseudomonad was added to nonsterile sewage, but the bacterium grew in sterile DCP-amended sewage, although not causing appreciable mineralization of the test compound. Addition of the bacterium to nonsterile soil did not result in the mineralization of 10 micrograms of DCP per g, although mineralization was evident if the inoculum was added to sterile soil. A second DCP-utilizing pseudomonad failed to mineralize DCP when added to the surface of sterile soil, although activity was evident if the inoculum was mixed with the soil. A pseudomonad able to mineralize 5.0 micrograms of PNP per ml in culture did not mineralize the compound in sterile or nonsterile lake water. The bacterium destroyed PNP in sterile sewage and enhanced PNP mineralization in nonsterile sewage. When added to the surface of sterile soil, the bacterium mineralized little of the PNP present at 5.0 micrograms/g, but it was active if mixed well with the sterile soil.(ABSTRACT TRUNCATED AT 250 WORDS)     

Rates of Mineralization of Trace Concentrations of Aromatic Compounds in Lake Water and Sewage Samples

The rates of mineralization of phenol, benzoate, benzylamine, p-nitrophenol, and di(2-ethylhexyl) phthalate added to lake water at concentrations ranging from a few picograms to nanograms per milliliter were directly proportional to chemical concentration. The rates were still linear at levels of <1 pg of phenol or p-nitrophenol per ml, but it was less than the predicted value at 1.53 pg of 2,4-dichlorophenoxyacetate per ml. Mineralization of 2,4-dichlorophenoxyacetate was not detected in samples of lake water containing 200 ng of the chemical per ml. The slope of a plot of the rate of phenol mineralization in samples of three lakes as a function of its initial concentration was lower at levels of 1 to 100 μg/ml than at higher concentrations. In lake water and sewage supplemented with <60 ng of ¹⁴C-labeled benzoate or phenylacetate per ml, 95 to 99% of the radioactivity disappeared from solution, indicating that the microflora assimilated little or none of the carbon. The extent of mineralization of some compounds in samples of two lakes and sewage was least in the water with the lowest nutrient levels. No mineralization of 2,4-dichlorophenoxyacetate and the phthalate ester was observed in samples of an oligotrophic lake. These data suggest that mineralization of some chemicals at concentrations of <1 μg/ml is the result of activities of organisms different from those functioning at higher concentrations or of organisms that metabolize the chemicals at low concentrations but assimilate little or none of the substrate carbon.     

Kinetic comparison of seven strains of 2,4-dichlorophenoxyacetic acid-degrading bacteria.

Seven strains of 2,4-dichlorophenoxyacetic acid-degrading bacteria, including Pseudomonas, Alcaligenes, and Bordetella spp., were compared on the basis of growth kinetics. Estimates of maximum growth rate (mu max, k1) and half-saturation growth constant (Ks, k3) were obtained by fitting substrate depletion curves to a four-parameter version of the integrated Monod equation. Estimates of Ks ranged from 2.2 micrograms/ml (10 microM) to 33.8 micrograms/ml (154 microM), and estimates of mu max ranged from 0.20 h-1 (Td = 3.5 h) to 0.32 h-1 (Td = 2.2 h). Estimates of mu max, but not Ks, were affected by changes in initial inoculum density. Maximum growth rates (mu max) were also estimated from turbidity measurements. They ranged from 0.10 h-1 (Td = 6.9 h) to 1.0 h-1 (Td = 0.7 h). There was no correlation between estimates of mu max derived from substrate depletion curves and those derived from turbidity measurements (P = 0.20).     

Kinetic comparison of seven strains of 2,4-dichlorophenoxyacetic acid-degrading bacteria.

Seven strains of 2,4-dichlorophenoxyacetic acid-degrading bacteria, including Pseudomonas, Alcaligenes, and Bordetella spp., were compared on the basis of growth kinetics. Estimates of maximum growth rate (mu max, k1) and half-saturation growth constant (Ks, k3) were obtained by fitting substrate depletion curves to a four-parameter version of the integrated Monod equation. Estimates of Ks ranged from 2.2 micrograms/ml (10 microM) to 33.8 micrograms/ml (154 microM), and estimates of mu max ranged from 0.20 h-1 (Td = 3.5 h) to 0.32 h-1 (Td = 2.2 h). Estimates of mu max, but not Ks, were affected by changes in initial inoculum density. Maximum growth rates (mu max) were also estimated from turbidity measurements. They ranged from 0.10 h-1 (Td = 6.9 h) to 1.0 h-1 (Td = 0.7 h). There was no correlation between estimates of mu max derived from substrate depletion curves and those derived from turbidity measurements (P = 0.20).