The gene appA, encoding a phytase from Yersinia kristeensenii, was cloned and heterologously expressed in Pichia pastoris. The open reading frame of appA comprised 1326 bp encoding a protein of 441 amino acids including a 24-amino acid signal peptide. The encoded phytase, APPA, was 87% identical to the phytase from Y. intermedia but was <52% identical to other histidine acid phosphatases. The purified recombinant phytase had an optimal activity at 55 degrees C and pH 4.5, and it exhibited enzymatic activity between pH 2.0 and 6.5, with a specific activity of 2656 U mg(-1) at pH 4.5 and 37 degrees C. r-APPA retained more than 90% of its initial activity after being incubated under varying pH conditions (pH 1.5-11.0) at 37 degrees C for 3 h. r-APPA was resistant to heat inactivation, as it retained 46% of its initial activity after incubation at 80 degrees C for 10 min. r-APPA was effective for the hydrolysis of phytate phosphorus from soybean meal in vitro. Comparison of r-APPA with other well-known phytases suggests that the Y kristeensenii phytase would be an attractive enzyme for feed industry use. (C) 2008 Elsevier Inc. All rights reserved.