The invention provides isolated and recombinant phytase enzymes. In one aspect, the phytases are produced by modification of the wild type appA of E. coli. The enzyme can be produced from recombinant host cells. The phytases of the invention can be used to aid in the digestion of phytate where desired. In particular, the phytases of the invention can be used in foodstuffs to improve the feeding value of phytate rich ingredients. The phytases of the invention can be thermotolerant and/or thermostable. Also provided are methods for obtaining a variant polynucleotide encoding a phytase and for obtaining a phytase with thermostability or thermotolerant at high or low temperatures.