Introduction to Buchnera

Symbiosis and Evolution

The intracellular symbiosis in the aphid bacteriocyte represents one of the most intimate interactions between a bacterium and the eukaryotic cell. Almost all aphid species have 60-80 cells called bacteriocytes, within which are host-derived vesicles containing round or oval-shaped bacteria that are designated Buchnera. The aphid embryo growing parthenogenetically in its mother's ovariole is infected with Buchnera at an early stage of development, and the endosymbiont is thereby transmitted from generation to generation of the host insect without having any free-living stage.
    The mutualism between Buchnera and the host is so obligate that neither associant could any longer reproduce independently. Although a number of functions have been hypothesized for the symbiont, one of the most important aspects of the host-symbiont relationship in this endosymbiosis is found in their nutritional interaction. This has often been discussed in conjunction with the fact the phloem sap on which aphids feed is rich in carbohydrates but poor in nitrogenous and other compounds. Buchnera are implicated in the supplementation of the aphids' diet, and there is now many evidences that they provide amino acids and vitamine to host insects.

   Buchnera are prokaryotic cells 1-2 um in diameter and belong to the gasmma-Proteobacteria, closely related to the Enterobacteriaceae family. Phylogenetic analysis, based on 16S rDNA sequences of Buchnera from numerous aphid species, has revealed that the symbiotic relationship was established 200-250 million years ago and led to cospeciation of the hosts and their symbionts.

    The genome sequence of a Buchnera species clearly indicates the evolutionary basis that underlies the marked difference in metabolism between the parasite and symbiont. In addition, since Buchnera are closely retated to Escherichia coli, comparison between their genomes facilitates direct estimation of the evolutionary consequences of endocellular life. Buchnera genome sequence is a perfect treasure for a broad range of biologists, including those interested in evolution, microbiology, ecological interactions, microbial pathogenesis, and comparative genomics.

More ....
My recommendations for studying Buchnera.

  • Shigenobu, S. et al. Genome sequence of the endocellular bacterial symbiont of aphids Buchnera sp.APS. Nature 407, 81-86 (2000).
    • Buchnera genome is telling us many things.
  • Baumann, P. et al. Genetics, physiology, and evolutionary relationships of the genus Buchnera: intracellular symbionts of aphids. Annu. Rev. Microbiol. 49, 55-94 (1995).
    • This is very good review.
  • Douglas, A. E. Nutritional interactions in insect-microbial symbioses: aphids and their symbiotic bacteria Buchnera. Annu. Rev. Entomol.  43, 17-37 (1998).
    • This review is focused on the nutritional interaction.
  • Houk, E. J. & Griffiths, G. W. Intracellular symbiotes of the Homopltera. Annu. Rev. Entomol.  25, 161-187 (1980).
    • This is old review, but informative.
  • Baumann, P., N.A. Moran, and L. Baumann. Bacteriocyte-associated endosymbionts of insects. In M. Dworkin (ed.),The Prokaryotes [Online.] Springer, New York, N. Y.(2000). http://link.springer.de/link/service/books/10125/
    • It is a new and excellent review, but expensive...


 

Buchnera (Photo by M. Morioka)


The bacteriocyte of the aphid
(Photo by T. Fukatsu). You can find the bacteriocyte is filled with the smaller cells. All of these are Buchnera. The larger circle located at the center is the nucleus of the host.


Interpretative drawing of the internal view of the aphid. (by T. Sasaki)


Aphids