A novel phytase gene appA from Buttiauxella sp. GC21 isolated from grass carp intestine

A novel phytase gene, appA, was isolated by degenerate PCR and genomic library screening from Buttiauxella sp. GC21, a bacterium isolated from grass carp intestine. The full-length gene consists of an open reading frame of 1341 bp and encodes 446 amino acids, including 33 amino acid residues of a putative signal peptide. Containing the active site of typical histidine acid phosphatases, the amino acid sequence shows maximum identity (71%) to PhyA from Obesumbacterium proteus. The gene encoding the mature phytase was expressed in Escherichia coli and the purified recombinant APPA had a specific activity for sodium phytate of 1180 U mg− 1 of protein. The optimum temperature was 55 °C and the optimum pH was 4.5. The Km value was 0.36 mM, with a Vmax of 1.39 mmol min− 1 mg− 1. This is the first report to detect and isolate a phytase from Buttiauxella sp.