Heddi A, Grenier A M, Khatchadourian C, Charles H, Nardon P
Laboratoire de Biologie Appliquée, Institut National des Sciences Appliquées-Institut National de la Recherche Agronomique Unité Associée 203, France.
Proc Natl Acad Sci U S A. 1999 Jun 8;96(12):6814-9. doi: 10.1073/pnas.96.12.6814.
Cell physiology in the weevil Sitophilus oryzae is coordinated by three integrated genomes: nuclear, mitochondrial, and the "S. oryzae principal endosymbiont" (SOPE). SOPE, a cytoplasmic bacterium (2 x 10(3) bacteria per specialized bacteriocyte cell and 3 x 10(6) bacteria per weevil) that belongs to the proteobacteria gamma3-subgroup, is present in all weevils studied. We discovered a fourth prokaryotic genome in somatic and germ tissues of 57% of weevil strains of three species, S. oryzae, Sitophilus zeamais, and Sitophilus granarius, distributed worldwide. We assigned this Gram-negative prokaryote to the Wolbachia group (alpha-proteobacteria), on the basis of 16S rDNA sequence and fluorescence in situ DNA-RNA hybridization (FISH). Both bacteria, SOPE and Wolbachia, were selectively eliminated by combined heat and antibiotic treatments. Study of bacteria involvement in this insect's genetics and physiology revealed that SOPE, which induces the specific differentiation of the bacteriocytes, increases mitochondrial oxidative phosphorylation through the supply of pantothenic acid and riboflavin. Elimination of this gamma3-proteobacterium impairs many physiological traits. By contrast, neither the presence nor the absence of Wolbachia significantly affects the weevil's physiology. Wolbachia, disseminated throughout the body cells, is in particularly high density in the germ cells, where it causes nucleocytoplasmic incompatibility. The coexistence of two distinct types of intracellular proteobacteria at different levels of symbiont integration in insects illustrates the genetic complexity of animal tissue. Furthermore, evolutionary timing can be inferred: first nucleocytoplasm, then mitochondria, then SOPE, and finally Wolbachia. Symbiogenesis, the genetic integration of long-term associated members of different species, in the weevil appears to be a mechanism of speciation (with Wolbachia) and provides a means for animals to acquire new genes that permit better adaptation to the environment (with SOPE).
米象（Sitophilus oryzae）的细胞生理学由三个整合的基因组协调：核基因组、线粒体基因组和“米象主要内共生菌”（SOPE）。SOPE是一种细胞质细菌（每个特化的含菌细胞中有2×10³个细菌，每只米象中有3×10⁶个细菌），属于γ-变形菌纲γ3亚群，在所研究的所有米象中都存在。我们在分布于全球的米象、玉米象（Sitophilus zeamais）和谷象（Sitophilus granarius）三个物种的57%的米象菌株的体细胞和生殖组织中发现了第四个原核基因组。基于16S rDNA序列和荧光原位DNA-RNA杂交（FISH），我们将这种革兰氏阴性原核生物归为沃尔巴克氏体属（α-变形菌纲）。通过热疗和抗生素联合处理可选择性地消除SOPE和沃尔巴克氏体这两种细菌。对细菌参与该昆虫遗传和生理过程的研究表明，诱导含菌细胞特异性分化的SOPE通过提供泛酸和核黄素增加线粒体氧化磷酸化。消除这种γ3-变形菌会损害许多生理特征。相比之下，沃尔巴克氏体的存在与否对米象的生理机能均无显著影响。沃尔巴克氏体分布于全身细胞，在生殖细胞中的密度尤其高，在那里它会导致核质不亲和。昆虫体内两种不同类型的细胞内变形菌在共生整合的不同水平上共存，说明了动物组织的遗传复杂性。此外，可以推断出进化时间顺序：先是核质，然后是线粒体，接着是SOPE，最后是沃尔巴克氏体。共生起源，即不同物种长期关联成员的遗传整合，在米象中似乎是一种物种形成机制（与沃尔巴克氏体有关），并为动物提供了一种获取新基因的途径，使其能够更好地适应环境（与SOPE有关）。
