Aksoy S, Chen X, Hypsa V
Department of Epidemiology and Public Health, Yale University, School of Medicine, New Haven, Connecticut 06510, USA.
Insect Mol Biol. 1997 May;6(2):183-90. doi: 10.1111/j.1365-2583.1997.tb00086.x.
Many tsetse species (Diptera: Glossinidae) harbour two morphologically different intracellular endosymbiotic microorganisms associated with gut tissue: primary (P) and secondary (S) endosymbionts. The P-endosymbionts of tsetse (Wigglesworthia glossinidia) are sequestered in specialized epithelial cells, bacteriocytes, which form a structure (bacteriome) in the anterior portion of the gut. Phylogenetic characterization of P-endsymbionts from the three subgenera of genus Glossina has shown that these organisms constitute a distinct lineage within the gamma-subdivision of Proteobacteria and have evolved concordantly with their insect host species, suggesting an evolutionarily ancient association for this symbiosis. The S-endosymbiont is a smaller (1-2 micron) gram-negative rod and is harboured in midgut epithelial cells. Its phylogenetic characterization from Glossina morsitans morsitans had shown that it is a member of the family Enterobacteriaceae within the gamma-3 subdivision of the Proteobacteria, closely related to enteric bacteria. Some tsetse species harbour a third bacterium in their reproductive tissue, which was shown phylogenetically to belong to to the Wolbachia pipientis assemblage of microorganisms. Here, we show that S-endosymbionts from five tsetse species, representing all three subgenera, form a cluster of closely related microorganisms, based on their almost identical 16S rRNA gene sequences. The high similarity provides strong evidence of recent independent acquisition of S-endosymbionts by individual tsetse species, unlike Wigglesworthia which displays concordant evolution with host insect species. A PCR-based assay and restriction fragment length polymorphism (RFLP) analysis was developed to localize the S-endosymbionts and Wigglesworthia in ovary, egg, milk-gland and spermatheca tissues in order to investigate the potential routes for the vertical transmission of these symbionts to the intrauterine larvae. Only S-endosymbionts were found to infect milk gland tissue, suggesting that milk gland secretions represent a route of transmission for these symbionts into the developing larva. The ovary tissue was found to harbour only Wolbachia, confirming its transovarial transmission, whereas the mode of transmission of Wigglesworthia remains unknown.
许多采采蝇物种（双翅目：舌蝇科）体内携带着两种形态不同的与肠道组织相关的细胞内共生微生物：初级（P）和次级（S）内共生体。采采蝇的P内共生体（格氏嗜菌共生菌）被隔离在特化的上皮细胞即含菌细胞中，这些细胞在肠道前部形成一个结构（菌瘤）。对舌蝇属三个亚属的P内共生体进行系统发育特征分析表明，这些生物体在变形菌门γ亚纲中构成一个独特的谱系，并且与其昆虫宿主物种协同进化，这表明这种共生关系在进化上由来已久。S内共生体是一种较小的（1 - 2微米）革兰氏阴性杆菌，存在于中肠上皮细胞中。对 morsitans morsitans采采蝇的S内共生体进行系统发育特征分析表明，它是变形菌门γ - 3亚纲肠杆菌科的一员，与肠道细菌密切相关。一些采采蝇物种在其生殖组织中携带着第三种细菌，系统发育分析表明它属于嗜菌属微生物组合。在这里，我们表明，基于代表所有三个亚属的五种采采蝇的S内共生体几乎相同的16S rRNA基因序列，它们形成了一组密切相关的微生物。这种高度相似性有力地证明了各个采采蝇物种近期独立获得了S内共生体，这与与宿主昆虫物种协同进化的格氏嗜菌共生菌不同。开发了一种基于PCR的检测方法和限制性片段长度多态性（RFLP）分析，以定位卵巢、卵、乳腺和受精囊组织中的S内共生体和格氏嗜菌共生菌，从而研究这些共生体垂直传播到子宫内幼虫的潜在途径。仅发现S内共生体感染乳腺组织，这表明乳腺分泌物是这些共生体进入发育中幼虫的一条传播途径。发现卵巢组织仅携带嗜菌属微生物，证实了其经卵巢传播，而格氏嗜菌共生菌的传播方式仍然未知。
