根虫瘟霉原始菌株及转寄主菌株在不同培养条件下胞外蛋白酶的诱导表达特性

通过比较根虫瘟霉Zoophthora radicans 3个菌株（原始菌株R₀、转寄主菌株R₁和R₅）在不同培养条件下诱导胞外蛋白酶的差异，发现在含昆虫表皮和明胶的培养基中，均能诱导表达高水平的胞外蛋白酶，而在营养缺乏的MS培养基和营养丰富的萨氏培养基中则胞外蛋白酶的表达水平均很低。37 kD的丝氨酸蛋白酶在任何条件下都能被诱导表达，是各菌株中的保守序列所编码的胞外蛋白酶。46 kD的金属蛋白酶仅能在含明胶的培养基中被诱导表达，而葡萄糖可抑制其表达。在萨氏培养基中，67 kD 的蛋白酶条带在转寄主过程中消失了，而46 kD的金属蛋白酶条带和117 kD的条带随着转寄主传代数增加而明显，表明菌株在转染过程中选择表达了对新寄主具有较高基质特异性的胞外蛋白酶。

Characteristics of inducible extracellular proteases expressed by Zoophthora radicans original and host-adapted strains under different culture conditions

A high level of protease activities were expressed both by Zoophthora radicans original strain(R_0)and host-adapted strains(R_1 and R_5)when they grew in MS medium containing insect cuticle or gelatin.On the contrary,very low level of protease activities were detected in extremely poor nutrient medium(MS)or rich nutrient medium(Sabouraud's dexteose broth,SDB).A 37 kD band belonging to serine protease was found to be induced in any cultural condition,suggesting it is a conservative sequence coding protease for three strains.On the other hand,a 46 kD band belonging to metalloprotease was expressed only in MS medium containing gelatin;however,its expression could be inhibited by MS medium containing glucose.Interestingly,a protease band with molecular weight of 67 kD disappeared,whereas the bands of 46 kD and 117 kD became more obvious for isolates after several infection cycles through Plutella xylostella when isolates grew in SDB medium.The results indicated that inducible high substrate-specific extracellular protease was greatly expressed to adapt to new host during passages of subculture through P.xylostella.