Microbial Transformation Rate Research Articles

Initial Test of the Benchmark Chemical Approach for Predicting Microbial Transformation Rates in Aquatic Environments

Using 2,4-dichlorophenoxyacetic acid methyl ester (2,4-DME) as a benchmark chemical, we determined relative pseudo-first-order rate coefficients for the butoxyethyl ester of 2,4-dichlorophenoxyacetic acid (2,4-DBE), methyl parathion, and methyl-3-chlorobenzoate in a diversity of microbial samples, including water, sediment, biofilm, and floating microbial mats collected from a laboratory mesocosm as well as from streams, lakes, and wetlands in Georgia and Florida. The decreasing order of reactivity for relative microbial transformation rates was 2,4-DBE > 2,4-DME > methyl-3-chlorobenzoate > methyl parathion. Half-lives of the chemicals varied about 60-fold depending on the chemical and microbial sample. Relative rate coefficients, however, typically varied only about threefold for field-collected samples. Relative rate coefficients determined with samples from a laboratory mesocosm were consistently low compared with the field sample data. Overall, the data indicated that microbial transformation rates of a chemical can be satisfactorily inferred for a wide variety of microbial habitats-such as water, biofilm, or a sediment-on the basis of its transformation rate relative to that of an appropriate benchmark chemical by using a single type of microbial sample.

Microbial degradation of seven amides by suspended bacterial populations.

Microbial transformation rate constants were determined for seven amides in natural pond water. A second-order mathematical rate expression served as the model for describing the microbial transformation. Also investigated was the relationship between the infrared spectra and the second-order rate constants for these amides. Second-order rate constants (k2) ranged from a low of 2.0 X 10(-14) to a high of 1.1 X 10(-9) liters organism-1 h-1 for niclosamide (2',5-dichloro-4'-nitrosalicylanilide) and propachlor (2-chloro-N-isopropylacetanilide), respectively. The mechanism of degradation (i.e., microbially mediated hydrolysis) of the amides was consistent with that of other organic chemicals previously studied in a variety of natural waters. Preliminary investigations indicate that temporal variations in measured second-order rate constants are small. A simple linear regression of the infrared carbonyl-stretching frequency with log K2 gave a correlation coefficient (r2) of 0.962.

Model-based relationship between the microbial transformation rate of organic chemicals and their physicochemical properties

Using the time hierarchy of the processes, determining the fate of foreign compounds in microbial cell suspensions, a simple kinetic description of biotransformation was derived considering both the boundary cases in the rate-concentration dependence of the pertinent enzymic reaction, namely the first and zero order kinetics. The decisive drug properties turned out to be hydrophobicity and the rate parameters of the transformation reaction. In accord with the results of the uptake experiments and contrary to the previous approaches, transport of organic molecules into the cell is not considered as the rate limiting step. The resulting equations are consistent with the literature data.

Prediction of Substrate Removal Rates of Attached Microorganisms and of Relative Contributions of Attached and Suspended Communities at Field Sites

A mathematical model composed of a direct proportionality relationship between bulk water velocities and field-determined second-order microbial transformation rate coefficients, and the relative rate coefficient of a benchmark chemical, was developed for estimating the substrate removal rates of rapidly degraded chemicals by attached organisms in shallow (<1 m deep) aquatic ecosystems. Data from 31 field experiments involving the addition of 2,4-dichlorophenoxyacetic acid methyl ester (2,4-DME) in nine field areas were used to determine a field-derived second-order rate coefficient for microbial transformation of the ester. By using 2,4-DME as a benchmark chemical, the model was used to predict microbial transformation rates of the butoxyethyl ester of 2,4-dichlorophenoxyacetic acid (2,4-DBE) at five other field sites. The predicted half-lives of 2,4-DBE varied 1,500-fold and were within about a threefold range or less of the measured half-lives. Under conditions of mass transport limitation, the contributions of attached microorganisms relative to total microbial activities at various field sites were related to the ratio of water velocity, U, and depth, D, showing that historical definitions of ecosystems according to flow and depth characteristics are also valid for describing the process-related structure of ecosystems. An equation was developed for predicting the relative contributions of attached and suspended communities with values of U and D for lotic and lentic ecosystems. On the basis of this equation, attached microorganisms were expected to be insignificant in deep lentic ecosystems and suspended microorganisms were expected to be insignificant in shallow lotic systems for the same process carried out by both populations. Neglecting epiphytic microorganisms, both suspended and attached organisms were expected to be significant in wetlands.

An analysis of continuous vertical nutrient profiles taken during a cold-anomaly off Peru

Continuous vertical profiles of nutrient concentrations to depths of ∼250 m with a vertical resolution of ∼2 m help to describe and explain conditions during a cold-anomaly in the waters off Peru. The data suggest that primary production (∼2 g C m 2 d 1) in the euphotic zone above an extraordinary shallow oxygen deficient zone (maximum nitrite value of 23 μM) was supported largely by vertical transports from a thin layer between 10 and 20 m. Calculations based on the profiles suggest that the denitrification rate in the shallow oxygen deficient feature (2–5 × 10 3 μmol m −2 d −1) was also supported by vertical diffusion. Both calculations are based on a vertical diffusion coefficient of 1 cm 2 s −1. Deeper oxygen deficient zones with secondary nitrite maxima embedded within them were also sampled; an unusual feature found north of 11°S centered at about 300 m and the main secondary nitrite maximum (MSNM) centred at about 200 m south of 11°S. Our data and calculations suggest that vertical diffusion was not the dominant control on denitrification rates in the northern feature. A possibly atypical station within the MSNM, however, revealed a steep vertical gradient at the relatively shallow upper boundary of the nitrite maximum. In this case, the denitrification rate required to balance losses through the upper boundary may have been on the order of 40% of the total rate. Comparison of the vertical nutrient profiles with variations in static stability shows structures with similar depth scales. The data also suggest that these features may arise from the interleaving of water masses with different histories and that the rates of microbial nitrogen transformations may display similar fine structure. A stability maximum is common at the upper boundary of the oxygen deficient zones, but our data agree with previous results suggesting that the nitrite maxima embedded within the cores of these features are not associated with unusually strong stratification.

Degradation of phenol and chlorophenols by sunlight and microbes in estuarine water

Download Hi-Res ImageDownload to MS-PowerPointCite This:Environ. Sci. Technol. 1986, 20, 10, 1002-1007

Seasonal effects on microbial transformation rates of an herbicide in a freshwater stream: Application of laboratory data to a field site

AbstractSeasonal effects on microbial transformation rates of an herbicide, 2,4‐dichlorophen‐oxyacetic acid butoxyethyl ester (2,4‐DBE), in a freshwater stream were investigated using low concentrations (less than 100 μg L−1) of the herbicide mixed with an inert dye, rhodamine WT, to correct for dilution. Although water temperatures decreased from 22 ± 0.5 to 8.0 ± 0.5°C and water velocities decreased from 0.09 ± 0.01 to 0.03 ± 0.003 m s−1, microbial transformation rates, as indicated by pseudo‐first‐order transformation rate coefficients, increased as much as threefold in the cold months over those in the spring and summer. The increased winter transformation rates were associated with leaf‐litter accumulation, which provided additional colonized surface area in the stream. Therefore, the increased colonized surface area more than compensated for the effects of temperature and water velocity (under conditions of mass‐transport limitation) that otherwise would have reduced microbial transformation rates in the winter months.

Microbial transformation rates of AZO and triphenylmethane dyes

AbstractUsing field‐collected and laboratory cultures, bacterial transformation rates for one azo and two triphenylmethane dyes were studied as a means of assessing the potential degradation of these compounds in aquatic environments. Transformation was measured as loss of color by spectrophotometry, and first‐ and second‐order transformation rate coefficients were determined. Second‐ order coefficients (kb) were based on total colony‐forming units (CFU) of bacteria in batch cultures. Percentages of total bacteria that transformed the dyes were determined by isolating bacterial colonies from field‐collected samples and testing the isolates for the capacity to transform the dyes in dilute nutrient medium. The azo dye, Acid Orange 6, was not transformed under the aerobic conditions of these studies. Basic Violet 1 was transformed and k1 values ranged from ‐0.003 to ‐0.023 h−1, with a mean (kb) of 3.5 × 10−14L CFU−1 h−1. Basic Violet 3 also was transformed and k1 values ranged from ‐0.002 to ‐0.012 h−1, with a mean kb of 2.8 × 10−14 L CFU−1 h−1. The percentage of transformer bacteria for Basic Violet 1 ranged from 6 to 28%, with a mean of 13.5%, and the range for Basic Violet 3 was 0 to 24%, with a mean of 8.32%. Therefore, the triphenylmethane dyes were transformed at similar rates, and similar fractions of the total bacterial populations were involved in the transformation.

MICROBIAL TRANSFORMATION RATES OF AZO AND TRIPHENYLMETHANE DYES

MICROBIAL TRANSFORMATION RATES OF AZO AND TRIPHENYLMETHANE DYES

Microbial Transformation of Esters of Chlorinated Carboxylic Acids

Two groups of compounds were selected for microbial transformation studies. In the first group were carboxylic acid esters having a fixed aromatic moiety and an increasing length of the alkyl component. Ethyl esters of chlorine-substituted carboxylic acids were in the second group. Microorganisms from environmental waters and a pure culture of Pseudomonas putida U were used. The bacterial populations were monitored by plate counts, and disappearance of the parent compound was followed by gas-liquid chromatography as a function of time. The products of microbial hydrolysis were the respective carboxylic acids. Octanol-water partition coefficients (K(ow)) for the compounds were measured. These values spanned three orders of magnitude, whereas microbial transformation rate constants (k(b)) varied only 50-fold. The microbial rate constants of the carboxylic acid esters with a fixed aromatic moiety increased with an increasing length of alkyl substituents. The regression coefficient for the linear relationships between log k(b) and log K(ow) was high for group 1 compounds, indicating that these parameters correlated well. The regression coefficient for the linear relationships for group 2 compounds, however, was low, indicating that these parameters correlated poorly.

Effect of Phenol Molecular Structure on Bacterial Transformation Rate Constants in Pond and River Samples

Microbial transformation rate constants for a series of phenols were correlated with a property of the substituents, van der Waal's radius. Transformation products were the corresponding catechols, with the exception of p-hydroxybenzoic acid, the product of p-acetylphenol. A different product suggested a different pathway; p-acetylphenol, therefore, was deleted from the data base.

Structure-Activity Relationships in Microbial Transformation of Phenols

The second-order rate constants for the microbial transformation of a series of phenols were correlated with the physicochemical properties of the phenols. The compounds studied were phenol, p-methylphenol, p-chlorophenol, p-bromophenol, p-cyanophenol, p-nitrophenol, p-acetylphenol, and p-methoxyphenol. Phenol-grown cells of Pseudomonas putida U transformed these compounds. Microbial transformation rate constants ranged from (1.5 +/- 0.99) x 10 liter . organism . h for p-cyanophenol to (7.0 +/- 1.3) x 10 liter . organism . h for phenol. Linear regression analyses of rate constants and electronic, steric, and hydrophobic parameters showed that van der Waal's radii gave the best coefficient of determination (r = 0.956). Products identified by thin-layer chromatography and liquid chromatography indicated that the phenols were microbially oxidized to the corresponding catechols.

Rates of Microbial Transformation of Polycyclic Aromatic Hydrocarbons in Water and Sediments in the Vicinity of a Coal-Coking Wastewater Discharge

To facilitate predictions of the transport and fate of contaminants at future coal conversion facilities, rates of microbial transformation of polycyclic aromatic hydrocarbons were measured in stream water and sediment samples collected in the vicinity of a coal-coking treated wastewater discharge from November 1977 through August 1979. Six radiolabeled polycyclic aromatic hydrocarbons were incubated with sediment and water samples; CO(2), cell-bound C, and polar transformation products were isolated and quantified. Whereas CO(2) and bound C were major transformation products in sediment assays, soluble polar C dominated transformation in water samples. Mean rate constants (measured at 20 degrees C) in sediments collected downstream from the effluent outfall were 7.8 x 10 h (naphthalene), 1.6 x 10 h (anthracene), and 3.3 x 10 h [benz(a)anthracene], which corresponded to turnover times of 13, 62, and 300 h, respectively. No unequivocal evidence for transformation of benzo(a)pyrene or dibenz(a,h)anthracene was obtained. Only naphthalene and anthracene transformations were observed in water samples; rate constants were consistently 5- and 20-fold lower, respectively, than in the corresponding sediment samples. The measured rate constants for anthracene transformation in July 1978 sediment samples were not related to total heterotroph numbers. In late July 1978, the effluent was diverted from the primary study area; however, no differences were observed either in transformation rate constants or in the downstream/upstream sediment rate constant ratio. These results are consistent with the hypothesis that continuous inputs of polycyclic aromatic hydrocarbons result in an increased ability within a microbial community to utilize certain polycyclic aromatic hydrocarbons. However, because transformation rates remained elevated for more than 1 year after removal of the polycyclic aromatic hydrocarbon source, microbial communities may shift only slowly in response to changes in polycyclic aromatic hydrocarbon concentrations.

Microbial Transformation of Polycyclic Aromatic Hydrocarbons in Pristine and Petroleum-Contaminated Sediments

To determine rates of microbial transformation of polycyclic aromatic hydrocarbons (PAH) in freshwater sediments, C-labeled PAH were incubated with samples from both pristine and petroleum-contaminated streams. Evolved CO(2) was trapped in KOH, unaltered PAH and polar metabolic intermediate fractions were quantitated after sediment extraction and column chromatography, and bound cellular C was measured in sediment residues. Large fractions of C were incorporated into microbial cellular material; therefore, measurement of rates of CO(2) evolution alone would seriously underestimate transformation rates of [C]naphthalene and [C]anthracene. PAH compound turnover times in petroleum-contaminated sediment increased from 7.1 h for naphthalene to 400 h for anthracene, 10,000 h for benz(a)anthracene, and more than 30,000 h for benz(a)pyrene. Turnover times in uncontaminated stream sediment were 10 to 400 times greater than in contaminated samples, while absolute rates of PAH transformation (micrograms of PAH per gram of sediment per hour) were 3,000 to 125,000 times greater in contaminated sediment. The data indicate that four- and five-ring PAH compounds, several of which are carcinogenic, may persist even in sediments that have received chronic PAH inputs and that support microbial populations capable of transforming two- and three-ring PAH compounds.

Deep-Sea Microorganisms: In situ Response to Nutrient Enrichment

After inoculation of sterile organic materials on the deep-sea floor and in situ incubation for 1 year, relatively minute rates of microbial transformation were recorded. This extremely slow conversion rate, as well as the type and quantity of organic matter normally reaching the ocean floor, appear to characterize microbial life in the deep sea.

GROWTH OF MARINE BACTERIA AT LIMITING CONCENTRATIONS OF ORGANIC CARBON IN SEAWATER1

Growth responses of several species of heterotrophic marine bacteria to limiting concentrations of lactate, glycerol, and glucose in seawater were determined in a chemostat. In all cases, threshold concentrations of the limiting substrates were found below which the organisms were unable to grow. This phenomenon is explained on the basis of a positive feedback mechanism, which is abolished below a certain minimum population density. The resulting inhibitory effect on growth leaves a corresponding concentration of the limiting substrate unattacked.According to their growth parameters, two types of species could be distinguished, one adapted to the marine environment by its ability to grow at low substrate concentrations and one inactive in natural seawater but surviving.The implications of these results on the rates of microbial transformations and on the occurrence and concentrations of dissolved organic material in the sea are discussed.