一株家蚕病原性微孢子虫的生物学特性与分子系统发育分析

从家蚕体内分离得到一株新的病原性微孢子虫,编号为GXM1。光学显微镜下观察GXM1微孢子虫为长卵圆形,大小(1.85±0.15)μm×(4.19±0.18)μm,在生活史的各发育阶段均为双核,以二分裂方式增殖,发育速度缓慢,发育周期约8～10 d。GXM1微孢子虫与家蚕微孢子虫(Nb)的抗血清产生阳性凝聚反应。利用透射电子显微镜观察到GXM1微孢子虫的超微结构具双核,极丝11～12圈,极丝倾斜角约45°。以上生物学性状显示GXM1微孢子虫具有微孢子虫属(Nosema)的基本分类特征。依据GXM1微孢子虫与其它昆虫微孢子虫的SSU rRNA基因序列构建的系统发育树,以及序列相似性和遗传距离分析,进一步证实GXM1微孢子虫属于Nosema属。GXM1微孢子虫对蚁蚕的半数感染浓度(IC50)为6.06×105mL-1,对家蚕的胚种传染率可达23.28%,是一株具有较强致病性和危害性的家蚕病原性微孢子虫。

Biological Characters and Molecular Phylogenetic Analysis of a Microsporidian Isolate Pathogenic to Bombyx mori

GXM1,a new pathogenic microsporidium,was isolated from the silkworm,Bombyx mori.Optical microscopic observation showed that the spore of GXM1 was long oval in shape and(1.85±0.15)μm×(4.19±0.18)μm in size.The spores had two nuclei at all developmental phases of life cycle and propagated in binary fission.Its developmental was slow.Its life cycle took about 8 to 10 days.There was positive coagulation reaction between GXM1 and the antiserum of Nosema bombycis(Nb).Transmission electron microscopic observation showed that microsporidian GXM1 was binuclear and had 11~12 polar filament coils.The tilt angle of polar filament was about 45°.These biological characters indicated that microsporidian GXM1 had the basic taxonomic features of Nosema.Phylogenetic analysis based on SSU rRNA sequences of GXM1 and other microsporidian strains and sequence similarity and genetic distance analyses further confirmed that microsporidian GXM1 belonged to the genus of Nosema.The 50% infectious concentration(IC50) of GXM1 to newly-hatched silkworm larvae was 6.06×105 mL-1,and the germinative infection rate reached 23.28%.GXM1 was a strain of pathogenic microspofidium which had strong infectivity and threat to Bombyx mori.