Browsing by Author "Van Staden, Jason"

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    Identification and characterisation of a Cryptococcus laurentii Abo 510 Phytase
    (Stellenbosch : Stellenbosch University, 2004-03) Van Staden, Jason; Bloom, M.; Van Zyl, Willem Heber; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Phosphorus is vital for growth of all life forms and is a fundamental component of nucleic acids, ATP and several other biological compounds. Oilseeds and cereal grains, two major constituents of the diet of animals, contain phytic acid, which is the main storage form of phosphorus in plant cells. Monogastric animals, such as poultry and pigs, are not capable of utilising the bound phosphorus in phytic acid since they do not produce phytase, the essential hydrolysing enzyme. Microbial phytase is therefore added to the animal feed to enhance the availability of phosphorus and thus minimise phosphorus pollution and phosphorus supplementation in diets. For a phytase to be effective in the poultry and swine industry, it needs to be able to release phytic acid phosphorus in the digestive tract, it must be thermostable to resist feed processing and must be inexpensive to produce. One approach for developing an efficient phytase for the animal feed industry is by identifying new phytases from microorganisms, plants and animals. In this study, 11 strains of the genus Cryptococcus were screened for 'phytase activity. Initially, a differential agar plate screening method was employed to determine if any Cryptococcus species were able to express phytase, after which production was confirmed in different liquid media. Cryptococcus laurentii Abo 510 was identified as a strain with significant phytase activity. The C. laurentii Abo 510 strain showed clear zones on the differentialmedia agar plates and the production of phytase at high levels was observed when using wet cells grown in liquid media. The C. laurentii Abo 510 strain produced maximal phytase activity at a relatively high temperature (62°C) and in an acidic pH range (pH 5.0). This phytase also showed a broad substrate specificity that may assist in the release of other phosphate compounds captured in feedstuff. Although the phytase did not require any metal ions for its activity, several metal ions caused inhibition of the phytase activity. The enzyme was stable when exposed to 70°C for up to 180 minutes with only 40% loss in activity. Phosphorus addition to the culture media and enzyme assay solution at concentrations exceeding 500 f.!Minhibited the phytase activity completely. Different carbon sources in the culture media also influenced the phytase activity. The enzyme was determined to be a cell wall-associated phytase with little intracellularactivity.