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 u tilization of PAM for N was investigated. Intracellular and extracellu lar amidase activity was measured over time in enrichment cultures whi ch used PAM as sole N source. Enzyme activity increased concomitant wi th cell growth and N removal from PAM. Cell growth, N removal and amid ase production were dependent upon readily-available C in the medium. Amidase activity and substrate specificity were determined for PAM-uti lizing enrichment cultures exposed to various N sources. Polyacrylamid e-specific amidase activity appears to be inducible, and not constitut ive, based on the lack of amidase activity in cultures supplied with o nly ammonium nitrate for N versus substantial activity when PAM was ad ded as an amendment with or without ammonium nitrate. Cultures amended with propionamide exhibited amidase activity largely specific for thi s small amide substrate, while cultures supplied with PAM as sole N so urce exhibited amidase activity Specific for formamide, propionamide a nd PAM. Amidase activity and substrate specificity were determined for PAM-treated and untreated agricultural field soils. Polyacrylamide-sp ecific amidase activity was higher in PAM-treated soil (14.86 +/- 14.0 mu g NH4+ released g(-1) soil) than in untreated soil (1.02 +/- 2.3 m u g NH4+ released g(-1) soil); activity specific for low molecular wei ght amides was slightly elevated or unchanged in PAM-treated soil as c ompared with untreated soil. (C) 1998 Published by Elsevier Science Lt d. All rights reserved.