Biosynthesis of phytases and phosphatases by <i>Aspergillus niger</i> 551

Abstract

The purpose of this study was to determine the ability of the Aspergillus niger 551 strain to produce phytases and phosphatases in 24 days shake cultures at a pH adjusted to 5.5 and a changing (uncontrolled) pH, in a medium containing 0.5% of glucose and 4% of starch. The fermentation process of the culture performed with no adjustment of the pH showed that the pH markedly decreased (to 2.25) on day five and maintained at the same level also on consecutive days. However, the results show that irrespective of the pH of the medium, the fungi synthesized the enzymes through 2.5 weeks, although maximum activity was observed on different days. It was found that although the biosynthesis of phytases and phosphatases began earlier (before day five) at constant of pH 5.5, significantly higher activities of dephosphorylating enzymes were observed in the cultures with uncontrolled pH. The highest phytases activity (0.77 U/ml) of the fungi was observed on day 14, while phosphatases activity (3.257 U_Pho/ml) was the highest on day 12. The synthesis of amylases began at the same time in both cultures (before day five), but the production of these enzymes was more efficient at a constant pH. The highest amylolytic activity was found on day 12. The proteolytic enzymes in both processes were synthesized at low levels.

Key words: Aspergillus niger, phytase, phosphatase, amylase, protease, starch.