| مستخلص: |
A yeast producing a cold-adapted phytase was isolated from Antarctic deep-sea sediment and identified as a Rhodotorula mucilaginosa strain JMUY14 of basidiomycetous yeasts. It was cultured in fermentation optimized by a response surface methodology based on the Box-Behnken design. The maximum activity of phytase reached 205.447 U ml−1, which was close to the predicted value of 201.948 U ml−1 and approximately 3.4 times higher than its initial activity. The extracellular phytase was purified by 15.2-fold to homogeneity with a specific activity of 31,635 U mg−1 by (NH4)2SO4 precipitation, and a combination of DEAE Sepharose Fast Flow, SP Sepharose Fast Flow, and Sephadex G-100. The molecular weight of the purified enzyme was estimated to be 63 kDa and its pI was 4.33. Its optimal temperature and pH were 50 °C and 5.0, respectively. Its activity was 85% at 37 °C, and showed good stability at pH 3.0∼7.0. When compared with mesophilic counterparts, the phytase not only exhibited a higher activity during 20∼30 °C but also had a low Km (247 µM) and high kcat (1394 s−1). The phytase activity was slightly stimulated in the presence of Mg2+, Fe2+, Fe3+, K+, Na+, Ca2+, EDTA, and EGTA and moderately inhibited by Cu2+, Zn2+, Mn2+, Ag+, PMSF, SDS, and phenylgloxal hydrate. It was resistant to both pepsin and trypsin. Since the phytase produced by the R. mucilaginosa JMUY14 showed a high specific activity, good pH stability, strong protease resistance, and high activity at low temperature, it has great potential for feed applications, especially in aquaculture. [ABSTRACT FROM AUTHOR] |
