Aksoy S, Pourhosseini A A, Chow A
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Insect Mol Biol. 1995 Feb;4(1):15-22. doi: 10.1111/j.1365-2583.1995.tb00003.x.
Tsetse flies (Diptera: Glossinidae) harbour two morphologically different endosymbionts intracellularly associated with gut tissue: a primary (P) and a secondary (S) organism. The P-endosymbiont is a gram-negative rod, 8-10 microns in size, and resides intracellularly within specialized cells, mycetocytes which are organized into an organelle (mycetome), in the anterior portion of the gut. The S-endosymbiont is a smaller (1-2 microns) gram-negative rod and is harboured in the epithelial sheath cells in midgut. Phylogenetic characterization of S-endosymbionts from taxonomically distant insects including tsetse flies has shown that they are related to the free-living bacterium, Escherichia coli, and are members of the family Enterobacteriaceae within the gamma-3 subdivision of Proteobacteria. In this study, a polymerase chain reaction (PCR) based assay was designed utilizing the conserved sequences of 16S rDNA in order to phylogenetically characterize the mycetome-associated P-endosymbionts directly from tsetse mycetome tissue. Analysis from five species of flies representing the three major subgenera of genus Glossina indicates that P-endosymbionts constitute a distinct lineage within the gamma-3 subdivision of Proteobacteria. Mycetome endosymbiont phylogeny appears to parallel the classic taxonomic assignments independently developed for their insect host species. This suggests an ancient association for this symbiosis, which may have subsequently radiated with time, giving rise to the current species of tsetse flies and their modern-day endosymbionts. Based on endosymbiont phylogeny, the fusca flies constitute the most ancient subgenus, followed by the morsitans and palpalis groups.
采采蝇（双翅目：舌蝇科）在细胞内与肠道组织相关联地携带着两种形态不同的内共生体：一种主要（P）内共生体和一种次要（S）内共生体。P内共生体是一种革兰氏阴性杆菌，大小为8 - 10微米，细胞内存在于特化细胞——菌血细胞中，这些菌血细胞在肠道前部组织成一个细胞器（菌血体）。S内共生体是一种较小的（1 - 2微米）革兰氏阴性杆菌，存在于中肠的上皮鞘细胞中。对包括采采蝇在内的分类学上距离较远的昆虫的S内共生体进行系统发育特征分析表明，它们与自由生活的细菌大肠杆菌相关，并且是变形菌门γ-3亚纲内肠杆菌科的成员。在本研究中，利用16S rDNA的保守序列设计了一种基于聚合酶链反应（PCR）的检测方法，以便直接从采采蝇菌血体组织中对与菌血体相关的P内共生体进行系统发育特征分析。对代表舌蝇属三个主要亚属的五种采采蝇的分析表明，P内共生体在变形菌门γ-3亚纲内构成一个独特的谱系。菌血体内共生体的系统发育似乎与为其昆虫宿主物种独立发展的经典分类学归属平行。这表明这种共生关系由来已久，可能随后随着时间推移而分化，产生了当前的采采蝇物种及其现代内共生体。基于内共生体的系统发育，fusc a采采蝇构成最古老的亚属，其次是morsitans和palpalis组。
