产植酸酶菌株的筛选

Natural Selection of Microorganism Producing Phytases

从20份天然样品中筛选出20余株发酵液植酸酶活力超过30IU／mL的胞外植酸酶产生菌。经过复筛，发现产植酸酶活力大于100IU／mL的菌株8珠，包括霉菌（pH5．5处测定）4株，酵母（pH2.5处测定）4株。酵母YP901、YP144、YP133发酵液活力分别达到284、265、265IU／mL；霉菌MP113的发酵液酶活力最高达189IU／mL。通过pH2．5和pH5．5处酶活力比较确定：酵母分泌的植酸酶为phyB型，霉菌分泌的植酸酶为phyA型。霉菌和酵母YP133、YP901的发酵液在60℃处理10min后，植酸酶的残存率分别为0、44％、82％。所筛选酵母分泌的植酸酶的耐热性优于霉菌的。

More than 20 wild-type strains producing extracellular phytases, phytases activities of all of which being higher than 30IU per mL liquid fermentation medium, have been selected from 20 natural samples. Chmparing phytases activities at pH2. 5 and at pH5. 5, We find that phytases produced by yeast are phyB and phytases produced by molds are phyA. Alter being mcu-bated at 60℃ for 10 min, the molds phytases are associated with a completely irreversible denaturation, and phytases of yeast YP133 and YP901 wereassociated with loss in enzymatic activities of 56 % and 20%, respectively. In the case of phytases treated at 55t for 10 min, phytases of yeast YP113, YP901 retain 100 % of their activities. However, those of molds only recover 50 % - 60 % of their activities. In contrast to molds phytases, yeast phytases display considerably higher thermostability.