Santos-Garcia Diego, Rollat-Farnier Pierre-Antoine, Beitia Francisco, Zchori-Fein Einat, Vavre Fabrice, Mouton Laurence, Moya Andrés, Latorre Amparo, Silva Francisco J
Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, Spain.
Genome Biol Evol. 2014 Apr;6(4):1013-30. doi: 10.1093/gbe/evu077.
Many insects harbor inherited bacterial endosymbionts. Although some of them are not strictly essential and are considered facultative, they can be a key to host survival under specific environmental conditions, such as parasitoid attacks, climate changes, or insecticide pressures. The whitefly Bemisia tabaci is at the top of the list of organisms inflicting agricultural damage and outbreaks, and changes in its distribution may be associated to global warming. In this work, we have sequenced and analyzed the genome of Cardinium cBtQ1, a facultative bacterial endosymbiont of B. tabaci and propose that it belongs to a new taxonomic family, which also includes Candidatus Amoebophilus asiaticus and Cardinium cEper1, endosymbionts of amoeba and wasps, respectively. Reconstruction of their last common ancestors' gene contents revealed an initial massive gene loss from the free-living ancestor. This was followed in Cardinium by smaller losses, associated with settlement in arthropods. Some of these losses, affecting cofactor and amino acid biosynthetic encoding genes, took place in Cardinium cBtQ1 after its divergence from the Cardinium cEper1 lineage and were related to its settlement in the whitefly and its endosymbionts. Furthermore, the Cardinium cBtQ1 genome displays a large proportion of transposable elements, which have recently inactivated genes and produced chromosomal rearrangements. The genome also contains a chromosomal duplication and a multicopy plasmid, which harbors several genes putatively associated with gliding motility, as well as two other genes encoding proteins with potential insecticidal activity. As gene amplification is very rare in endosymbionts, an important function of these genes cannot be ruled out.
许多昆虫体内都携带着遗传的细菌内共生体。尽管其中一些并非严格必需，被认为是兼性的，但在特定环境条件下，如寄生蜂攻击、气候变化或杀虫剂压力下，它们可能是宿主生存的关键。烟粉虱是造成农业损害和爆发的生物之首，其分布变化可能与全球变暖有关。在这项研究中，我们对烟粉虱的兼性细菌内共生体卡氏菌cBtQ1的基因组进行了测序和分析，并提出它属于一个新的分类家族，该家族还包括亚洲嗜阿米巴菌和卡氏菌cEper1，分别是变形虫和黄蜂的内共生体。对它们最后共同祖先的基因内容进行重建发现，自由生活的祖先最初发生了大量基因丢失。随后，卡氏菌发生了较小规模的基因丢失，这与在节肢动物体内定居有关。其中一些影响辅因子和氨基酸生物合成编码基因的丢失发生在卡氏菌cBtQ1与卡氏菌cEper1谱系分化之后，与它在粉虱及其内共生体中的定居有关。此外，卡氏菌cBtQ1基因组显示出很大比例的转座元件，这些元件最近使基因失活并导致染色体重排。该基因组还包含一个染色体重复和一个多拷贝质粒，该质粒含有几个可能与滑行运动相关的基因，以及另外两个编码具有潜在杀虫活性蛋白质的基因。由于基因扩增在共生体中非常罕见，不能排除这些基因具有重要功能。
