Polyacrylamide as a substrate for microbial amidase in culture and soil

Abstract

Summary-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 hydrdlytic 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.

Polyacrylamide preparations for protection of water quality threatened by agricultural runoff contaminants

“…Bacterial enrichment cultures, derived from PAMtreated field soils, were capable of growth with PAM as a sole source of N, but could not grow with PAM as sole C source, whereas AMD served as a sole source of both N and C for bacterial growth (Kay-Shoemake et al, 1998b). A unique PAM-specific amidase has been described (Kay-Shoemake et al, 1998a, b).…”

“…This enzyme, which is apparently induced by the presence of PAM in soils, breaks amide linkages found in PAM, releasing NH4 , which is rapidly taken up by bacteria during growth. In laboratory incubations, 20% N was removed from added PAM preparations over a period of 120 h (Kay-Shoemake et al, 1998b).…”

“…PAM-specific amidase activity has been documented in laboratory cultures, as well as in field soil samples, following exposure to PAM (Kay-Shoemake et al, 1998b) The enzyme appears to have a broad substrate range, exhibiting activity against formamide and propionamide, but does not dramatically impact degradation rates of carbaryl, diphenamid or naphthalene acetamide in PAM-treated soils (Kay-Shoemake et al, 2000a). Both intracellular and extracellular activity have been noted, and production and secretion of the enzyme appears to be dependent on C availability, as cells cannot derive C directly from PAM.…”

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

“…The flow rate was 7.61 min' The microcosms received this treatment for approximately 1 year prior to the experiment. Soils, collected from the upper 3 cm of each sampled furrow bottom, were assayed for PAM-specific amidase activity by a previously described procedure (Kay-Shoemake et al 1998b), which is a modification of an assay originally described by Frankenberger and Tabatabai (1980a). The PAM-treated microcosm soil exhibited elevated PAM-specific amidase activity; untreated soil showed negligible activity.…”

“…Field studies indicate that PAM-treated agricultural soils exhibit elevated soil amidase activity that is specific for the PAM polymer (Kay-Shoemake et al 1998b). It is unclear from the laboratory and field data whether the PAM-induced amidase activity is indicative of a single amidase with broad specificity or of a group of enzymes, each with different amide specificity.…”