Plant-based animal feed normally contains phytic acid, which is not efficiently digested by monogastric animals due to the lack of phytate-hydrolyzing enzymes in their gastrointestinal tracts. Adding phytase into the feed will improve its quality, but it will certainly increase the cost of production because phytase bears high manufacturing costs, poor stability, and low specific activity of the enzyme in the animal’s intestinal conditions.
BIOTEC research team of Bioresources Technology Unit has been findingways to tackle this problem, utilizing the rich bioresources in Thailand. First, phytases have been screened from various fungi in BIOTEC Culture Collection. Among these, A. niger BCC18081 and Aspergillus japonicus BCC18313 were shown to produce phytases that can function at pH 3 and 5.5, conditions similar to animal intestine. Subsequently, genes encoding these two phytases were cloned and expressed in Pichia pastoris KM71. The recombinant phytases, r-PhyA170 and r-PhyA86, exhibited high thermostability, and functioned as efficiently as the commercial phytase in the in-vitro digestibility test.
However, secreted phytases producing from recombinant yeast still require tedious downstream processes such as purification and separation. To circumvent this problem, cell-surface technology was employed to anchor protein, phytase in this case, on the cell surface. Dr. Piyanun Harnpicharnchai et al., Researcher from Microbial Cell Factory Laborabory, has successfully expressed phytase r-PhyA170 as a cell-surface protein in P. pastoris. The cell-surface phytase exhibited high activity with an optimal temperature at 50–55 °C and two optimal pH peaks of 3 and 5.5. Compared to the native and secreted phytase, the cell-surface phytase exhibited similar pH stability, pepsin resistance and ability to release phosphorus from feedstuff in the in vitro digestibility test. Moreover, yeast cells expressing phytase also provide additional nutrients, especially biotin and niacin. Thus, P. pastoris with phytase displayed on its surface has a great potential as a whole-cell supplement to animal feed.
For more information on this study, please review the publication titled “Cell-surface phytase on Pichia pastoris cell wall offers great potential as a feed supplement". (FEMS Microbiology Letters 302, 8–14 (2010)).
Posted on 16 August 2010.