磷酸盐对V族大肠杆菌素形成的影响

含ColV质粒的大肠杆菌在含有磷酸盐的牛肉膏蛋白胨培养基上形成的菌落,当覆盖敏感菌后可以形成较大的抑菌圈。说明磷酸盐对ColV质粒所编码的V族大肠杆菌素的形成有促进作用。在培养基中加入二价离子螯合剂——EDTA对大肠杆菌素形成同样有促进作用,而增加二价阳离子Ca++或Mg++却起到相反的作用。磷酸盐的这种促进作用是由于它降低了牛肉膏蛋白胨培养基中二价阳离子的浓度而引起的。因此,在培养基中添加磷酸盐有助于分离ColV质粒含有菌和对V族大肠杆菌素的研究。

EFFECT OF PHOSPHATE ON COLICIN V FORMATION BY STRAINS OF ESCHERICHIA COLI

ColV~+ strains of Escherichia coli produced larger inhibitory zones when these strains grown on nutrient agar containing phosphate after overlaid sensitive indicators. This appears that production of colicin V is increased by the addition of phosphate to nutrient agar. It was sure that stimulation of phosphate to colicin V formation results from its effect in reducing divalent cation levels in nutrient agar since adding EDTA to nutrient agar had the same effect as phosphate, but the addition of Mg~(2+) or Ca~(2+) had the oppsite effect. Therefore nutrient agar supplemented with phosphate can be used to isolate and identificate ColV~+ strains of E. coli.