ARS | Publication request: Ethanol tolerance in Aspergillus niger and Escherichia coli phytase

Submitted to: Advances in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 18, 2012
Publication Date: September 1, 2012
Citation: Mullaney, E.J., Sethumadhavan, K., Boone, S., Ullah, A.H.J. 2012. Ethanol tolerance in Aspergillus niger and Escherichia coli phytase. Advances in Microbiology. 2(3):395-398.

Interpretive Summary: The expanded use of corn and other grains for biofuels has resulted in an increase in the supply of an ethanol fermentation by-product, dried grains with soluble (DDGS). DDGS is high in nutritive value and has a potential for expanded utilization in animal feed. However, the high levels of phytic acid found in some samples of DDGS has slowed it expansion in this market. Phytic acid is common in grains and while it is high in phosphorus it is in a form that animals with simple digestive tracts (swine, poultry, etc.) cannot digest. Since the yeast used in fermentation has its own phytase, which breaks down phytic acid, the high levels of phytic acid in DDGS suggest that the ethanol produced in fermentation inhibits phytase. In this study two commercial phytases were tested for ethanol tolerance. Significant differences were found in the tolerance of these two enzymes for ethanol. This supports the notion that the ethanol tolerance of the yeast’s phytase can also be increased. This would lower the phytic acid level in DDGS and thus raise it value as an animal feed component.

Technical Abstract: The expanded use of corn and other grain for biofuels have created an increased supply of dried grains with soluble (DDGS) and other byproducts of ethanol fermentation. Elevated levels of phytic acid in this DDGS indicate that ethanol is denaturing the native phytase produced by the yeast, Saccharomyces cerevisiae, generally utilized in fermentation. Reducing the phytic acid level in DDGS is desirable because it would broaden its utilization in animal feed. Ethanol is known to inactivate other hydrolytic enzymes but its effect on phytases is relatively unknown. In this study two phytases, one from Aspergillus niger (PhyA) and one from Escherichia coli (AppA2) were tested for ethanol tolerance. The efficacy of the phytase activity assay protocol with ethanol was established to insure accuracy. Significant difference in ethanol tolerance was found in the 5 to 10% range. Ethanol inactivation was found to be reversible for both enzymes. These differences in ethanol tolerance do suggest there is a potential to achieve higher ethanol tolerance in phytases to lower phytic acid levels in DDGS and for other applications.