Bandi C, Sironi M, Damiani G, Magrassi L, Nalepa C A, Laudani U, Sacchi L
Istituto di Patologia Generale Veterinaria, Università di Milano, Italy.
Proc Biol Sci. 1995 Mar 22;259(1356):293-9. doi: 10.1098/rspb.1995.0043.
All cockroaches examined so far have been found to harbour a bacterial endosymbiont in specialized cells of the fat body, whereas Mastotermes darwiniensis is the only termite currently known to harbour an intracellular symbiont. The localization and mode of transmission of these bacteria are surprisingly similar, but so far no data have been published on their phylogenetic relationships. To address this issue, molecular sequence data were obtained from the genes encoding the small subunit ribosomal RNA of the M. darwiniensis endosymbiont, and compared with those obtained from endosymbionts of seven species of cockroaches. Molecular phylogenetic analysis unambiguously placed all these bacteria among the flavobacteria-bacteroides, indicating that the endosymbiont of M. darwiniensis is the sister group to the cockroach endosymbionts examined. Additionally, nucleotide divergence between the endosymbionts appears to be congruent with the palaeontological data on the hosts's evolution. These results support previous claims that the original infection occurred in an ancestor common to cockroaches and termites. A loss of endosymbionts should subsequently have occurred in all termite lineages, except that which gave rise to M. darwiniensis.
到目前为止，所有被检测的蟑螂都被发现其脂肪体的特殊细胞中含有一种细菌内共生体，而达尔文澳白蚁是目前已知的唯一一种含有细胞内共生体的白蚁。这些细菌的定位和传播方式惊人地相似，但到目前为止，尚未有关于它们系统发育关系的数据发表。为了解决这个问题，从编码达尔文澳白蚁内共生体小亚基核糖体RNA的基因中获取了分子序列数据，并与从七种蟑螂的内共生体中获得的数据进行了比较。分子系统发育分析明确地将所有这些细菌归入黄杆菌-拟杆菌类，这表明达尔文澳白蚁的内共生体是所检测的蟑螂内共生体的姐妹群。此外，内共生体之间的核苷酸差异似乎与宿主进化的古生物学数据一致。这些结果支持了先前的说法，即最初的感染发生在蟑螂和白蚁的共同祖先中。随后，除了产生达尔文澳白蚁的那个谱系外，所有白蚁谱系中都应该发生了内共生体的丢失。
