Department of Genetics and Forestry and Agriculture Biotechnology Institute, University of Pretoria, Hillcrest, Pretoria ZA0002, South Africa.
J Econ Entomol. 2010 Jun;103(3):887-97. doi: 10.1603/ec09257.
Symbiosis allows an insect access to imbalanced food sources on which other organisms cannot survive. A bacterial endosymbiont, Buchnera aphidicola, gives aphids the ability to feed on phloem depleted of certain essential amino acids by producing those required. Pseudogenes and lower plasmid copy numbers of essential amino acid genes in B. aphidicola, endosymbiont of the Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), suggest that this symbiotic relationship is degenerating. The complete endosymbiont assemblages, copy numbers of plasmids (important in essential amino acid production), and sequence variation in B. aphidicola, from 10 Russian wheat aphid biotypes, were investigated. B. aphidicola was found to be monosymbiotic in the Russian wheat aphid biotypes and other Diuraphis species examined. An insert, occurring in an inverted repeat region on the leucine plasmid, was the only variation found in the approximately 10-kb B. aphidicola sequence analyzed from each Russian wheat aphid biotype. This inverted repeat was shown previously to be conserved within the family Aphididae. The insert occurred in B. aphidicola sequences isolated from four Russian wheat aphid biotypes. Copy numbers of the leucine plasmid differ between the South African and U.S. biotypes and were similar to previously reported values for biotypes from the same geographic regions. These results suggest that B. aphidicola may still contribute to Russian wheat aphid fitness when the aphid feeds on a variety of hosts.
共生使昆虫能够利用其他生物无法生存的营养失衡的食物源。一种名为 Buchnera aphidicola 的细菌内共生体使蚜虫能够通过产生所需的氨基酸来吸食缺少某些必需氨基酸的韧皮部。俄罗斯麦蚜（Diuraphis noxia（Kurdjumov））（半翅目：蚜虫科）的内共生体 Buchnera aphidicola 的假基因和必需氨基酸基因的质粒拷贝数较低，表明这种共生关系正在退化。对来自 10 个俄罗斯麦蚜生物型的完整内共生体组合、质粒拷贝数（对必需氨基酸产生很重要）以及 Buchnera aphidicola 的序列变异进行了研究。在俄罗斯麦蚜生物型和其他研究的 Diuraphis 物种中发现 Buchnera aphidicola 是单共生的。在从每个俄罗斯麦蚜生物型分析的大约 10kb 的 Buchnera aphidicola 序列中发现了一个仅在亮氨酸质粒的反向重复区发生的插入。此前，该反向重复被证明在蚜科内是保守的。该插入发生在从四个俄罗斯麦蚜生物型分离的 Buchnera aphidicola 序列中。亮氨酸质粒的拷贝数在南非和美国生物型之间存在差异，与之前报道的来自同一地理区域的生物型的值相似。这些结果表明，当蚜虫以各种宿主为食时，Buchnera aphidicola 可能仍然有助于俄罗斯麦蚜的适应性。
