Summary auto-generated
This study isolated and characterized phytase genes from two filamentous fungi: Aspergillus terreus strain 9A-1 and Myceliophthora thermophila. Phytases are enzymes that hydrolyze phytate (myo-inositol hexakisphosphate) into inorganic phosphate and other products. Using degenerate PCR primers based on known acid phosphatase sequences, researchers obtained partial gene sequences and screened genomic libraries to obtain complete phytase genes. The A. terreus phytase (466 amino acids) and M. thermophila phytase (487 amino acids) genes each contain a single intron. Both encoded proteins showed 48-60% amino acid identity to the previously characterized Aspergillus niger phytase, but only 21-29% identity to other histidine acid phosphatases. When expressed in A. niger, both proteins exhibited clear preference for phytic acid as substrate, with pH optima between 5.5 and 6.0. These enzyme activity profiles and substrate specificities distinctly differed from the A. niger pH 2.5-optimum acid phosphatase. Based on sequence homology and enzymatic characteristics, the three phytases form a novel subfamily within the histidine acid phosphatase family.
Key findings
- Novel phytase genes were isolated from A. terreus and M. thermophila fungi through PCR and genomic library screening
- Both phytases showed 48-60% amino acid identity to A. niger phytase but only 21-29% identity to other acid phosphatases, indicating they form a distinct subfamily
- Both enzymes preferred phytic acid as substrate with pH optima around 5.5-6.0, differing significantly from other acid phosphatases
- Each phytase gene contained a single intron (48 bp in A. terreus, 57 bp in M. thermophila)
- These phytases have potential applications as feed additives to improve phosphorus utilization in animal nutrition and reduce phosphorus pollution from agricultural waste
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Abstract
Phytases catalyse the hydrolysis of phytate (myo-inositol hexakisphosphate) to myo-inositol and inorganic phosphate. In this study genes encoding novel phytases from two different filamentous fungi, Aspergillus terreus strain 9A-1 and Myceliophthora thermophila were isolated. The encoded PhyA phytase proteins show 60% (A. terreus) and 48% (M. thermophila) identity, respectively, to the PhyA of Aspergillus niger and have 21-29% identity compared to other histidine acid phosphatases. All three PhyA proteins, in contrast to the A. niger pH 2.5-optimum acid phosphatase, prefer phytic acid as substrate and show enzyme activity at a broad range of acidic pH values. Based on their enzyme characteristics and protein sequence homology, the phytases form a novel subclass of the histidine acid phosphatase family.