Effect of inorganic nutrients on the acclimation period preceding mineralization of organic chemicals in lake water.

The addition of phosphate, nitrate, or sulfate (each at 10 mM) decreased the acclimation period for the mineralization of low concentrations of p-nitrophenol (PNP) in lake water. Added phosphate shortened the acclimation period for biodegradation of 2 ng to 2 micrograms of PNP per ml in various lake water samples and of 2,4-dichlorophenoxyacetate at 100 ng/ml. Added P enhanced the rate of growth of PNP-mineralizing microorganisms in waters containing 200 ng or 2 micrograms of PNP per ml. We suggest that the effect of P on the acclimation period results from an increase in the growth rate of the initially small population of microorganisms able to mineralize the synthetic chemicals.     

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)     

Inoculum size as a factor limiting success of inoculation for biodegradation

A study was conducted to determine the role of inoculum size of a bacterium introduced into nonsterile lake water in the biodegradation of a synthetic chemical. The test species was a strain of Pseudomonas cepacia able to grow on and mineralize 10 ng to 30 micrograms of p-nitrophenol (PNP) per ml in salts solution. When introduced into water from Beebe Lake at densities of 330 cells per ml, P. cepacia did not mineralize 1.0 microgram of PNP per ml. However, PNP was mineralized in lake water inoculated with 3.3 X 10(4) to 3.6 X 10(5) P. cepacia cells per ml. In lake water containing 1.0 microgram of PNP per ml, a P. cepacia population of 230 or 120 cells per ml declined until no cells were detectable at 13 h, but when the initial density was 4.3 X 10(4) cells per ml, sufficient survivors remained after the initial decline to multiply at the expense of PNP. The decline in bacterial abundance coincided with multiplication of protozoa. Cycloheximide and nystatin killed the protozoa and allowed the bacterium to multiply and mineralize 1.0 microgram of PNP, even when the initial P. cepacia density was 230 or 360 cells per ml. The lake water contained few lytic bacteria. The addition of KH2PO4 or NH4NO3 permitted biodegradation of PNP at low cell densities of P. cepacia. We suggest that a species able to degrade a synthetic chemical in culture may fail to bring about the same transformation in natural waters, because small populations added as inocula may be eliminated by protozoan grazing or may fail to survive because of nutrient deficiencies.     

Inoculum size as a factor limiting success of inoculation for biodegradation.

A study was conducted to determine the role of inoculum size of a bacterium introduced into nonsterile lake water in the biodegradation of a synthetic chemical. The test species was a strain of Pseudomonas cepacia able to grow on and mineralize 10 ng to 30 micrograms of p-nitrophenol (PNP) per ml in salts solution. When introduced into water from Beebe Lake at densities of 330 cells per ml, P. cepacia did not mineralize 1.0 microgram of PNP per ml. However, PNP was mineralized in lake water inoculated with 3.3 X 10(4) to 3.6 X 10(5) P. cepacia cells per ml. In lake water containing 1.0 microgram of PNP per ml, a P. cepacia population of 230 or 120 cells per ml declined until no cells were detectable at 13 h, but when the initial density was 4.3 X 10(4) cells per ml, sufficient survivors remained after the initial decline to multiply at the expense of PNP. The decline in bacterial abundance coincided with multiplication of protozoa. Cycloheximide and nystatin killed the protozoa and allowed the bacterium to multiply and mineralize 1.0 microgram of PNP, even when the initial P. cepacia density was 230 or 360 cells per ml. The lake water contained few lytic bacteria. The addition of KH2PO4 or NH4NO3 permitted biodegradation of PNP at low cell densities of P. cepacia. We suggest that a species able to degrade a synthetic chemical in culture may fail to bring about the same transformation in natural waters, because small populations added as inocula may be eliminated by protozoan grazing or may fail to survive because of nutrient deficiencies.     

Role of chemical concentration and second carbon sources in acclimation of microbial communities for biodegradation

A study was conducted to determine the role of concentration of the test chemical, of a second organic compound, and of mutation in the acclimation period before the mineralization of organic compounds in sewage. The acclimation period for the mineralization in sewage of 2 micrograms of 4-nitrophenol (PNP) per liter increased from 6 to 12 days in the presence of 10 mg of 2,4-dinitrophenol per liter. The extension of the acclimation period was equivalent to the time required for mineralization of 2,4-dinitrophenol. In contrast, the time for acclimation for the degradation of 2 micrograms of PNP per liter was reduced when 10 or 100 mg of phenol per liter was added. Lower phenol levels increased the acclimation period to 8 days. The length of the acclimation period for PNP mineralization decreased as the initial concentration of PNP increased from 2 micrograms to 100 mg/liter. The acclimation period for phenol mineralization was lengthened as the phenol concentration increased from 100 to 1,400 mg/liter. The length of the acclimation period for PNP and phenol biodegradation was reproducible, but it varied among replicates for the biodegradation of other nitro-substituted compounds added to sewage or lake water, suggesting that a mutation was responsible for acclimation to these other compounds. The acclimation period may thus reflect the time required for the destruction of toxins, and it also may be affected by the concentration of the test compound or the presence of other substrates.     

Role of chemical concentration and second carbon sources in acclimation of microbial communities for biodegradation.

A study was conducted to determine the role of concentration of the test chemical, of a second organic compound, and of mutation in the acclimation period before the mineralization of organic compounds in sewage. The acclimation period for the mineralization in sewage of 2 micrograms of 4-nitrophenol (PNP) per liter increased from 6 to 12 days in the presence of 10 mg of 2,4-dinitrophenol per liter. The extension of the acclimation period was equivalent to the time required for mineralization of 2,4-dinitrophenol. In contrast, the time for acclimation for the degradation of 2 micrograms of PNP per liter was reduced when 10 or 100 mg of phenol per liter was added. Lower phenol levels increased the acclimation period to 8 days. The length of the acclimation period for PNP mineralization decreased as the initial concentration of PNP increased from 2 micrograms to 100 mg/liter. The acclimation period for phenol mineralization was lengthened as the phenol concentration increased from 100 to 1,400 mg/liter. The length of the acclimation period for PNP and phenol biodegradation was reproducible, but it varied among replicates for the biodegradation of other nitro-substituted compounds added to sewage or lake water, suggesting that a mutation was responsible for acclimation to these other compounds. The acclimation period may thus reflect the time required for the destruction of toxins, and it also may be affected by the concentration of the test compound or the presence of other substrates.     

Growth of phenol-mineralizing microorganisms in fresh water.

A method was developed to enumerate the procaryotic and eucaryotic phenol-mineralizing microorganisms present in samples of fresh water. Sixty-five percent or greater mineralization of [U-14C]phenol was considered a positive tube (contained phenol-mineralizing microorganisms) in the most-probable-number technique. Replicate most-probable-number tubes contained no microbial inhibitors, streptomycin and tetracycline, or cyclohexamide and nystatin plus 200 pg to 100 micrograms of phenol per ml. Phenol mineralization rates were obtained by measuring the amount of exogenous phenol that disappeared from solution over time in the presence or absence of the microbial inhibitors. Initially, less than 100 phenol-mineralizing bacteria per ml and 1 phenol-mineralizing fungus per ml were present at both 200 pg and 100 micrograms of phenol per ml. Phenol mineralization rates were 6.3 times greater for the mineralizing bacteria than for the fungi at 200 pg of phenol per ml. Phenol concentrations above 10 micrograms/ml were inhibitory to the microorganisms capable of mineralizing phenol. The phenol mineralizers grew in the water samples in the absence of phenol, indicating that there were sufficient indigenous nutrients in the lake water to support growth. There was no difference in the growth rate of these microorganisms in the presence or absence of 1 ng of phenol per ml, whereas the growth rate was more rapid at 1 microgram of phenol per ml than in its absence. There was a correlation between microbial growth and the amount of phenol mineralized at 1 microgram but not at 1 ng of phenol per ml.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth of phenol-mineralizing microorganisms in fresh water

A method was developed to enumerate the procaryotic and eucaryotic phenol-mineralizing microorganisms present in samples of fresh water. Sixty-five percent or greater mineralization of [U-14C]phenol was considered a positive tube (contained phenol-mineralizing microorganisms) in the most-probable-number technique. Replicate most-probable-number tubes contained no microbial inhibitors, streptomycin and tetracycline, or cyclohexamide and nystatin plus 200 pg to 100 micrograms of phenol per ml. Phenol mineralization rates were obtained by measuring the amount of exogenous phenol that disappeared from solution over time in the presence or absence of the microbial inhibitors. Initially, less than 100 phenol-mineralizing bacteria per ml and 1 phenol-mineralizing fungus per ml were present at both 200 pg and 100 micrograms of phenol per ml. Phenol mineralization rates were 6.3 times greater for the mineralizing bacteria than for the fungi at 200 pg of phenol per ml. Phenol concentrations above 10 micrograms/ml were inhibitory to the microorganisms capable of mineralizing phenol. The phenol mineralizers grew in the water samples in the absence of phenol, indicating that there were sufficient indigenous nutrients in the lake water to support growth. There was no difference in the growth rate of these microorganisms in the presence or absence of 1 ng of phenol per ml, whereas the growth rate was more rapid at 1 microgram of phenol per ml than in its absence. There was a correlation between microbial growth and the amount of phenol mineralized at 1 microgram but not at 1 ng of phenol per ml.(ABSTRACT TRUNCATED AT 250 WORDS)     

Phosphorus enhancement of mineralization of low concentrations of p-nitrophenol by Flavobacterium sp. in lake water

Abstract A study was conducted to determine whether the supply of inorganic phosphorus in lake water was sufficient for the mineralization of p -nitrophenol (PNP) by a Flavobacterium sp. The bacterium grew following its inoculation into sterile lake water amended with only 20 or 200 ng PNP per ml, but depending on when the water sample was taken, either PNP was not mineralized or it was mineralized slowly. PNP at both concentrations was rapidly mineralized if 10 mM P was added. The degradation of 200 ng PNP per ml was most rapid if the lake water was amended with 10 mM P, it proceeded more slowly with 1 mM P and the initiation of mineralization was delayed to equal extents if the sterile water received 0.1 mM, 0.01 mM or no P. The possible significance of these findings to biodegradation in natural waters is discussed.     

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)     

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.     

Accelerated Biodegradation of High and Low Concentrations of p-Nitrophenol (PNP) by Bacterial Inoculation in Industrial Wastewater: The Role of Inoculum Size on Acclimation Period

The effect of inoculum size on the acclimation period and rate and extent of p-nitrophenol (PNP) degradation at high (1–10 mg/L) and low (26 μg/L) concentrations for two bacteria was determined in defined media as well as industrial wastewater. Increased inoculum size did not affect the acclimation period of either bacterium at high (1–10 mg/L) PNP concentrations. At low PNP concentrations (26 μg/L), the two bacteria behaved differently. The acclimation period was shortened and both the rate and extent of mineralization of PNP were enhanced by increasing the Corynebacterium sp. inoculum size from 3 × 10⁵ to 3 × 10⁶ cells/ml. Addition of phosphate or elimination of predators also reduced the acclimation period. Conversely, increasing the inoculum size from 3 × 10⁵ to 5 × 10⁶ cells/ml of Pseudomonas putida lengthened the acclimation period and reduced both the rate and extent of mineralization. It is suggested that, in a given environment, the success of an introduced species to enhance the degradation of a chemical depends upon (i) concentration of the chemical, (ii) selection of an appropriate microorganism, and (iii) utilization of a suitable inoculum size. Received: 1 April 1996 / Accepted: 6 May 1996     

Effects of organic compounds on the degradation ofp-nitrophenol in lake and industrial wastewater by inoculated bacteria

Many microorganisms fail to degrade pollutants when introduced in different natural environments. This is a problem in selecting inocula for bioremediation of polluted sites. Thus, a study was conducted to determine the success of four inoculants to degradep-nitrophenol (PNP) in lake and industrial wastewater and the effects of organic compounds on the degradation of high and low concentrations of PNP in these environments.Corynebacterium strain Z4 when inoculated into the lake and wastewater samples containing 20 µg/ml of PNP degraded 90% of PNP in one day. Addition of 100 µg/ml of glucose as a second substrate did not enhance the degradation of PNP and the bacterium utilized the two substrates simultaneously. Glucose used at the same concentration (100 µg/ml), inhibited degradation of 20 µg of PNP in wastewater byPseudomonas strain MS. However, glucose increased the extent of degradation of PNP byPseudomonas strain GR. Phenol also enhanced the degradation of PNP in wastewater byPseudomonas strain GR, but had no effect on the degradation of PNP byCorynebacterium strain Z4.Addition of 100 µg/ml of glucose as a second substrate into the lake water samples containing low concentration of PNP (26 ng/ml) enhanced the degradation of PNP and the growth ofCorynebacterium strain Z4. In the presence of glucose, it grew from 2×10⁴ to 4×10⁴ cells/ml in 3 days and degraded 70% of PNP as compared to samples without glucose in which the bacterium declined in cell number from 2×10⁴ to 8×10³ cells/ml and degraded only 30% PNP. The results suggest that in inoculation to enhance biodegradation, depending on the inoculant, second organic substrate many play an important role in controlling the rate and extent of biodegradation of organic compounds.Abbreviations PNP p-nitrophenol     

Selecting inocula for the biodegradation of organic compounds at low concentrations

The inability of many organisms to degrade pollutants at low concentrations is a problem when selecting inocula for bioremediation of sites with these low concentrations. Thus, a study was conducted to determine the effect of low concentrations of p-nitrophenol (PNP) on growth of four PNP-degrading bacteria and their abilities to metabolize low concentrations of the compound in culture and samples from an oligotrophic lake. PNP did not increase the growth rates of Flavobacterium sp. M4, Pseudomonas sp. K, Flavobacterium sp. M1, and Pseudomonas sp. SP3 at concentrations of less than 2, 4, 10, and 100 ng/ml, respectively, when it was the sole added carbon source in culture, but it stimulated multiplication at higher concentrations. In liquid culture with the nitro compound as sole added carbon source, the four bacteria extensively mineralized PNP at 50 and 100 ng/ml, and three of the four degraded much of the substrate at 25 ng/ml. Pseudomonas sp. SP3 mineralized more than 20% but the two Flavobacterium strains converted less than 10% of the substrate to C02 at 10 ng/ml, and none of the three mineralized more than 5% at 1 and 5 ng PNP/ml. Under conditions where more than 99% of the radioactivity from ¹⁴C-PNP added at 1 ng/ml remained in solution, two of the isolates formed organic products. Pseudomonas sp. K had no activity at 1, 5, and 10 ng/ml. In contrast, when each of the bacteria was separately inoculated into samples of water from an oligotrophic lake and from a well in which PNP was not biodegraded, the bacteria were able to mineralize as little as 1 ng PNP/ml. The addition to a salts solution of 10 ng of glucose per ml resulted in mineralization of PNP at concentrations too low to be mineralized when the nitro compound was the sole source of added carbon. Bacteria may thus be able to mineralize substrates in natural waters at concentrations below those suggested by tests conducted in culture media, possibly because of the availability of other carbon sources for the bacteria.Offprint requests to: M. Alexander.     

Anomalies in mineralization of low concentrations of organic compounds in lake water and sewage

The rates of mineralization of nitrilotriacetic acid (NTA), 2,4-dichlorophenoxyacetic acid (2,4-D), p-nitrophenol, aniline, and isopropyl N-phenylcarbamate (IPC) at one or more concentrations ranging from 100 pg/ml to 1.0 microgram/ml were proportional to chemical concentrations in samples of three lakes. The rates at 100 pg of NTA, 2,4-D, p-nitrophenol, and aniline per ml in samples of one or more lakes were less than predicted, assuming the rates were linearly related to the concentration. Neither NTA nor 2,4-dichlorophenol at 2.0 ng/ml was mineralized in some lake waters, but higher levels of the two chemicals were converted to CO2 in samples of the same waters. In samples from two lakes, little or no mineralization of IPC or 2,4-D occurred at 1.0 microgram/ml, but 10 ng/ml or lower levels of the herbicides were mineralized. The mineralization in sewage of 1.0 microgram of NTA per ml was biphasic; about 20% of the substrate was mineralized in 20 h, and mineralization was only reinitiated after a period of 130 h. The biphasic transformation was not a result of the accumulation of organic products, and it was still evident if protozoan activity was inhibited. NTA also underwent a biphasic mineralization in lake waters, and the biphasic pattern was not altered by additions of growth factors and inorganic nutrients. From 40 to 60% of the carbon of aniline added to lake water at levels of 100 pg/ml to 1.0 microgram/ml was mineralized, but more than 90% of the carbon of NTA, 2,4-D, or p-nitrophenol added to lake water at 10 ng/ml or 1.0 microgram/ml was mineralized.(ABSTRACT TRUNCATED AT 250 WORDS)