Buchnera sp. Crystal Thomas
The Friend of the Aphid
Acyrthosiphon pisum - the aphid
The Buchnera sp. are round-shaped prokaryotic organisms that are endocellular symbionts to aphids. They belong to the gamma-Proteobacteria, which is closely related to the Enterobacteriaceae family. Once a very close relative to E. coli, Buchnera sp. now only contains about 600 genes - one seventh of the genes in E. coli. Buchnera sp. are symbionts to aphids because they lack many of the organelles that are required to freely live in the world. The aphids also benefit from them because they live in low nutrient environments and the Buchnera provide them with amino acids. Buchnera sp. evolution has led it to a state of symbiont/organelle.
Buchnera - electron micrograph Aphid bacteriocyte
Aphids contain bacteriocytes in which Buchnera sp. live. The Buchnera sp. are transferred from the mother aphid to the embryo during its early development. This allows the Buchnera sp. to be passed on without living freely in the environment. Genome sequencing data from Buchnera sp. APS (one of the strains) has shown that this relationship was started 200-250 million years ago. It is also known that the two could not reproduce without each other.
The Buchnera sp. lack many essential genes. These genes code for the sugars that are needed to make cell components, regulatory proteins that are needed to adapt to changes in the environment, respiratory genes that allow the organism to produce food, and it also lacks genes for a DNA repair system that is vital to combat often fatal changes made in genes by UV damage. The aphid provides a constant enclosed environment for the bacteria and a food source so that the Buchnera sp. are able to survive. Since aphids live in nutrient deprived environments they lack some of the amino acids they need to make essential proteins. Buchnera makes these amino acids available to the aphids.
This organism brings up some interesting questions. Namely, at what point will this bacteria be renamed an organelle. It is much like a mitochondria, which is also dependent on the cell for life. The loss of part of its genome has now left it with only 1 rRNA, 32 tRNAs, and 2 plasmids (pTrp and pLeu). So scientist will continue to monitor the evolution of Buchnera.
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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