Polyacrylamide as an organic nitrogen source for soil microorganisms with potential effects on inorganic soil nitrogen in agricultural soil

Linear polyacrylamide (PAM) is gaining considerable acceptance as an effective anti-erosion additive in irrigation water. The potential effects of repeated PAM application on soil microbial ecology and the potential for biotransformation of this polymer in soils are not completely known. Untreated and PAM-treated soils (coarse-silty, mixed, mesic Durixerollic Calciorthids) were collected from agricultural fields near Kimberly, ID. Soils were analyzed to determine the effects of PAM treatment on bacterial counts and inorganic N concentrations and the potential for PAM biotransformation. Culturable heterotrophic bacterial numbers were significantly elevated in PAM-treated soil for the plot planted to potatoes; this effect was not observed in the plot planted to dry pink beans. Total bacterial numbers, determined by AODC, were not altered by PAM treatment in any of the soils sampled. Polyacrylamide-treated soil planted to potatoes contained significantly higher concentrations of NO3 and NH 3 (36.7 ± 2.20 and 1.30 ± 0.3 mg kg-1 , respectively) than did untreated soil (10.7 ± 2.30 and 0.50 ± 0.02 mg kg-1, respectively). For bean field soil there was no difference between treated and untreated soil inorganic N concentrations. Enrichment cultures generated from PAM-treated and untreated soils utilized PAM as sole N source, but not as sole C source. While the monomeric constituents of PAM, acrylamide and acrylic acid, both supported bacterial growth as sole C source, the PAM polymer did not. Enrichment cultures that used PAM for N exhibited amidase activity specific for PAM as well as smaller aliphatic amides. Utilization of PAM for N, but not for C, indicates that ultimately PAM may be converted into long chain polyacrylate, which may be further degraded by physical and biological mechanisms or be incorporated into organic matter

Polyacrylamide as a substrate for microbial amidase in culture and soil

High molecular weight, linear polyacrylamide (PAM) with anionic charge is added to agricultural soils as an anti-erosion additive. Research indicates that soil microorganisms are able to utilize PAM as a source of N and that inorganic N pools are altered in some PAM-treated soils. The potential role of hydrolytic amidase activity in the microbial utilization of PAM for N was investigated. Intracellular and extracellular amidase activity was measured over time in enrichment cultures which used PAM as sole N source. Enzyme activity increased concomitant with cell growth and N removal from PAM. Cell growth, N removal and amidase production were dependent upon readily-available C in the medium. Amidase activity and substrate specificity were determined for PAM-utilizing enrichment cultures exposed to various N sources. Polyacrylamide-specific amidase activity appears to be inducible, and not constitutive, based on the lack of amidase activity in cultures supplied with only ammonium nitrate for N versus substantial activity when PAM was added as an amendment with or without ammonium nitrate. Cultures amended with propionamide exhibited amidase activity largely specific for this small amide substrate, while cultures supplied with PAM as sole N source exhibited amidase activity specific for formamide, propionamide and PAM. Amidase activity and substrate specificity were determined for PAM-treated and untreated agricultural field soils. Polyacrylamide-specific amidase activity was higher in PAM-treated soil (14.86 ± 14.0 pg NH4 released soil) than in untreated soil (1.02 ± 2.3 pg NH4 released C I soil); activity specific for low molecular weight amides was slightly elevated or unchanged in PAM-treated soil as compared with untreated soil

Soil amidase activity in polyacrylamide-treated soils and potential activity toward common amide-containing pesticides

t Polyacrylamide (PAM) is currently used as an irrigation water additive to significantly reduce the amount of soil erosion that occurs during furrow irrigation of crops. Elevated soil amidase activity specific toward the large PAM polymer has been reported in PAM-treated field soils; the substrate specificity of the induced amidase is uncertain. PAM-treated and untreated soils were assayed for their capacity to hydrolyze the amide bond in carbaryl (Sevin), diphenamid (Dymid), and naphthalene acetamide. Based on results obtained with a soil amidase assay, there was no difference between PAM-treated and untreated soils with respect to the rate of amide bond hydrolysis of any of the agrochemicals tested. It appears that under these assay conditions the PAM-induced soil amidase is not active toward the amide bonds within these molecules. However, carbaryl was hydrolyzed by a different soil amidase. To our knowledge, this is the first soil enzyme assay-based demonstration of the hydrolysis of carbaryl by a soil amidase

Stable Carbon Isotope Fractionation in Chlorinated Ethene Degradation by Bacteria Expressing Three Toluene Oxygenases

One difficulty in using bioremediation at a contaminated site is demonstrating that biodegradation is actually occurring in situ. The stable isotope composition of contaminants may help with this, since they can serve as an indicator of biological activity. To use this approach it is necessary to establish how a particular biodegradation pathway affects the isotopic composition of a contaminant. This study examined bacterial strains expressing three aerobic enzymes for their effect on the 13C/12C ratio when degrading both trichloroethene (TCE) and cis-1,2-dichloroethene (c-DCE): toluene 3-monoxygenase, toluene 4-monooxygenase, and toluene 2,3-dioxygenase. We found no significant differences in fractionation among the three enzymes for either compound. Aerobic degradation of c-DCE occurred with low fractionation producing δ13C enrichment factors of −0.9 ± 0.5 to −1.2 ± 0.5, in contrast to reported anaerobic degradation δ13C enrichment factors of −14.1 to −20.4‰. Aerobic degradation of TCE resulted in δ13C enrichment factors of −11.6 ± 4.1 to −14.7 ± 3.0‰ which overlap reported δ13C enrichment factors for anaerobic TCE degradation of −2.5 to −13.8‰. The data from this study suggest that stable isotopes could serve as a diagnostic for detecting aerobic biodegradation of TCE by toluene oxygenases at contaminated sites

Polyacrylamide as a substrate for microbial amidase in culture and soil

High molecular weight, linear polyacrylamide (PAM) with anionic charge is added to agricultural soils as an anti-erosion additive. Research indicates that soil microorganisms are able to utilize PAM as a source of N and that inorganic N pools are altered in some PAM-treated soils. The potential role of hydrolytic amidase activity in the microbial utilization of PAM for N was investigated. Intracellular and extracellular amidase activity was measured over time in enrichment cultures which used PAM as sole N source. Enzyme activity increased concomitant with cell growth and N removal from PAM. Cell growth, N removal and amidase production were dependent upon readily-available C in the medium. Amidase activity and substrate specificity were determined for PAM-utilizing enrichment cultures exposed to various N sources. Polyacrylamide-specific amidase activity appears to be inducible, and not constitutive, based on the lack of amidase activity in cultures supplied with only ammonium nitrate for N versus substantial activity when PAM was added as an amendment with or without ammonium nitrate. Cultures amended with propionamide exhibited amidase activity largely specific for this small amide substrate, while cultures supplied with PAM as sole N source exhibited amidase activity specific for formamide, propionamide and PAM. Amidase activity and substrate specificity were determined for PAM-treated and untreated agricultural field soils. Polyacrylamide-specific amidase activity was higher in PAM-treated soil (14.86 ± 14.0 pg NH4 released soil) than in untreated soil (1.02 ± 2.3 pg NH4 released C I soil); activity specific for low molecular weight amides was slightly elevated or unchanged in PAM-treated soil as compared with untreated soil

Soil amidase activity in polyacrylamide-treated soils and potential activity toward common amide-containing pesticides

t Polyacrylamide (PAM) is currently used as an irrigation water additive to significantly reduce the amount of soil erosion that occurs during furrow irrigation of crops. Elevated soil amidase activity specific toward the large PAM polymer has been reported in PAM-treated field soils; the substrate specificity of the induced amidase is uncertain. PAM-treated and untreated soils were assayed for their capacity to hydrolyze the amide bond in carbaryl (Sevin), diphenamid (Dymid), and naphthalene acetamide. Based on results obtained with a soil amidase assay, there was no difference between PAM-treated and untreated soils with respect to the rate of amide bond hydrolysis of any of the agrochemicals tested. It appears that under these assay conditions the PAM-induced soil amidase is not active toward the amide bonds within these molecules. However, carbaryl was hydrolyzed by a different soil amidase. To our knowledge, this is the first soil enzyme assay-based demonstration of the hydrolysis of carbaryl by a soil amidase

Polyacrylamide as an organic nitrogen source for soil microorganisms with potential effects on inorganic soil nitrogen in agricultural soil

Linear polyacrylamide (PAM) is gaining considerable acceptance as an effective anti-erosion additive in irrigation water. The potential effects of repeated PAM application on soil microbial ecology and the potential for biotransformation of this polymer in soils are not completely known. Untreated and PAM-treated soils (coarse-silty, mixed, mesic Durixerollic Calciorthids) were collected from agricultural fields near Kimberly, ID. Soils were analyzed to determine the effects of PAM treatment on bacterial counts and inorganic N concentrations and the potential for PAM biotransformation. Culturable heterotrophic bacterial numbers were significantly elevated in PAM-treated soil for the plot planted to potatoes; this effect was not observed in the plot planted to dry pink beans. Total bacterial numbers, determined by AODC, were not altered by PAM treatment in any of the soils sampled. Polyacrylamide-treated soil planted to potatoes contained significantly higher concentrations of NO3 and NH 3 (36.7 ± 2.20 and 1.30 ± 0.3 mg kg-1 , respectively) than did untreated soil (10.7 ± 2.30 and 0.50 ± 0.02 mg kg-1, respectively). For bean field soil there was no difference between treated and untreated soil inorganic N concentrations. Enrichment cultures generated from PAM-treated and untreated soils utilized PAM as sole N source, but not as sole C source. While the monomeric constituents of PAM, acrylamide and acrylic acid, both supported bacterial growth as sole C source, the PAM polymer did not. Enrichment cultures that used PAM for N exhibited amidase activity specific for PAM as well as smaller aliphatic amides. Utilization of PAM for N, but not for C, indicates that ultimately PAM may be converted into long chain polyacrylate, which may be further degraded by physical and biological mechanisms or be incorporated into organic matter