|Hoang, Khanh - INST TROP BIOL, VIET NAM|
Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 16, 2008
Publication Date: May 19, 2008
Repository URL: http://hdl.handle.net/10113/21871
Citation: Dao, T.H., Hoang, K.Q. 2008. Dephosphorylation and Quantification of Organic Phosphorus in Poultry Litter by Purified Phytic-Acid High Affinity Aspergillus Phosphohydrolases. Chemosphere. 72:1782-1787. (http://dx.doi.org/10.1016/j.chemosphere.2008.04.048)Chemosphere. Interpretive Summary: Over 650 million broilers were produced in DE and MD Eastern Shore in 2006. Concerns are raised about nutrient accumulation and surpluses as manures are generated at rates exceeding the storage and assimilation capacity of these regions. Poultry litter has a particularly high content of feed organic phytate. Land application of poultry litter often lead to nutrient-enriched soils, in particular soil high in phosphorus. The breakdown of phytic acid is effected by phytases enzymes that are produced by a wide variety of bacteria, yeasts, fungi, and plants. Current research on phytases and commercial enzyme production has largely focused on applications as animal feed supplement. Recently, the enzymes are used as a mean of detecting environmental P pollution. For such a purpose, extracellular enzymes must be stable and robust in complex environmental specimens. Scientists at BARC-EMBUL determine the effects of culture conditions on the growth and induction of extracellular phytases in five selected fungal strains and use the purified preparations to evaluate their stability and phytate-degrading ability. The enzymes produced in-house were equivalent to commercial enzyme preparations, showing that organic enzyme-labile P occurred at an average of 54 or more % of total phosphorus in poultry litters from Maryland and Oklahoma, while a total of 73% occurs as water-insoluble inorganic and organic P reserves. Therefore, litter management practices and land application options must take into account their high P content and that over 3/4 of that water insoluble P reserves is in organic enzyme-labile P forms.
Technical Abstract: Extracellular phosphohydrolases have received increased attention as they are shown to influence the behavior and bioavailability of environmental phosphorus, which pose risks of impairment of surface waters and degradation of sensitive aquatic ecosystems. Induction and culture of five strains of Aspergillus were conducted to develop a source of high-affinity and robust phosphohydrolases for quantifying bioactive P pools in heterogeneous environmental specimens. Enzyme stability and their hydrolytic activity against organic phosphorus in poultry feed and litter were evaluated in a set of 71 samples collected across Maryland and Oklahoma. Differences existed in adaptability of Aspergillus strains to the culture medium as they showed a wide range in phytate-degrading activity. Phosphohydrolases from A. ficuum, showed highest phytic acid-degrading potential when the strain was cultured on a primarily chemical medium, as opposed to A. oryzae which preferred a wheat bran-based organic medium. Kinetics parameters of the A. ficuum enzymes (Km = 210 µmol l-1 and Vmax of 407 nkat) indicated phytic acid-degrading potential equivalent to a commercial enzyme preparation. Bulk preparations of the purified A. ficuum phosphohydrolases were effective in quantifying the litter bioactive P pools, showing that organic phosphomonoesters or organic enzyme-labile P occurred in significant concentration, at an average of 54 ±15, compared to 41 ± 12 % of TP as water-extractable and insoluble inorganic phosphate-P. Litter management practices and land application options must take into account their high P content and the biological availability of the organic enzyme-labile P pool.