Buchnera (proteobacteria)
Encyclopedia
Buchnera aphidicola a member of the Proteobacteria
, is the primary endosymbiont of aphids
and has been studied in the pea aphid, Acyrthosiphon pisum. It is believed that Buchnera was once a free living gram negative ancestor similar to a modern Enterobacteriaceae
such as Escherichia coli. Buchnera are 3 µm in diameter and have some of the key characteristics of their Enterobacteriaceae relatives such as a gram-negative cell wall. However, unlike most other gram-negative bacteria, Buchnera lack the genes to produce lipopolysaccharides (LPS) for their outer membrane. The long association with aphids and the limitation of crossover
events due to strictly vertical transmission has seen the deletion of genes required for anaerobic respiration
, the synthesis of amino sugars, fatty acids, phospholipids, and complex carbohydrates. This has resulted not only in one of the smallest known genomes of any living organism, it is also one of the most genetically stable.
The symbiotic
relationship with aphids began between 160 million and 280 million years ago, and has persisted through maternal transmission and co-speciation
. Aphids have developed bacteriocyte
cells to house Buchnera. It is estimated that a mature aphid
may carry 5.6 × 106 Buchnera individuals. Buchnera have lost regulatory factors, allowing continuous overproduction of tryptophan
and other amino acids. Each bacteriocyte contains multiple vesicles
, symbiosomes derived from the plasma membrane.
Buchnera also increase the transmission of plant virus
es by producing symbionin, a protein
that binds to the viral coat and protects it inside the aphid. This makes it more likely that the virion will survive and be able to infect another plant when the aphid next feeds.
Buchnera was first named by Paul Baumann and his graduate student, and the first molecular characterization of a symbiotic bacterium was carried out by Baumann, using Buchnera. The initial studies on Buchnera later led to studies on symbionts of many groups of insects, pursued by numerous investigators, including Paul and Linda Baumann, Nancy Moran, Serap Aksoy, Roy Gross, who together investigated symbionts of aphids, tsetse flies, ants, leafhoppers, mealybugs, whiteflies, psyllids and others.
Proteobacteria
The Proteobacteria are a major group of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera....
, is the primary endosymbiont of aphids
Aphid
Aphids, also known as plant lice and in Britain and the Commonwealth as greenflies, blackflies or whiteflies, are small sap sucking insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions...
and has been studied in the pea aphid, Acyrthosiphon pisum. It is believed that Buchnera was once a free living gram negative ancestor similar to a modern Enterobacteriaceae
Enterobacteriaceae
The Enterobacteriaceae is a large family of bacteria that includes many of the more familiar pathogens, such as Salmonella, Escherichia coli, Yersinia pestis, Klebsiella and Shigella. This family is the only representative in the order Enterobacteriales of the class Gammaproteobacteria in the...
such as Escherichia coli. Buchnera are 3 µm in diameter and have some of the key characteristics of their Enterobacteriaceae relatives such as a gram-negative cell wall. However, unlike most other gram-negative bacteria, Buchnera lack the genes to produce lipopolysaccharides (LPS) for their outer membrane. The long association with aphids and the limitation of crossover
Chromosomal crossover
Chromosomal crossover is an exchange of genetic material between homologous chromosomes. It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis in a process called synapsis. Synapsis begins before the synaptonemal complex develops, and is not completed...
events due to strictly vertical transmission has seen the deletion of genes required for anaerobic respiration
Anaerobic respiration
Anaerobic respiration is a form of respiration using electron acceptors other than oxygen. Although oxygen is not used as the final electron acceptor, the process still uses a respiratory electron transport chain; it is respiration without oxygen...
, the synthesis of amino sugars, fatty acids, phospholipids, and complex carbohydrates. This has resulted not only in one of the smallest known genomes of any living organism, it is also one of the most genetically stable.
The symbiotic
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
relationship with aphids began between 160 million and 280 million years ago, and has persisted through maternal transmission and co-speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
. Aphids have developed bacteriocyte
Bacteriocyte
A bacteriocyte , also called a mycetocyte, is a specialized adipocyte found in some insect groups such as aphids, tsetse flies, german cockroaches, and many others. Mycetocyte symbionts specifically include three insect groups: Cockroaches, Homoptera such as aphid, and Coleoptera such as weevils...
cells to house Buchnera. It is estimated that a mature aphid
Aphid
Aphids, also known as plant lice and in Britain and the Commonwealth as greenflies, blackflies or whiteflies, are small sap sucking insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions...
may carry 5.6 × 106 Buchnera individuals. Buchnera have lost regulatory factors, allowing continuous overproduction of tryptophan
Tryptophan
Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG...
and other amino acids. Each bacteriocyte contains multiple vesicles
Vesicle (biology)
A vesicle is a bubble of liquid within another liquid, a supramolecular assembly made up of many different molecules. More technically, a vesicle is a small membrane-enclosed sack that can store or transport substances. Vesicles can form naturally because of the properties of lipid membranes , or...
, symbiosomes derived from the plasma membrane.
Buchnera also increase the transmission of plant virus
Plant virus
Plant viruses are viruses that affect plants. Like all other viruses, plant viruses are obligate intracellular parasites that do not have the molecular machinery to replicate without a host. Plant viruses are pathogenic to higher plants...
es by producing symbionin, a protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that binds to the viral coat and protects it inside the aphid. This makes it more likely that the virion will survive and be able to infect another plant when the aphid next feeds.
Buchnera was first named by Paul Baumann and his graduate student, and the first molecular characterization of a symbiotic bacterium was carried out by Baumann, using Buchnera. The initial studies on Buchnera later led to studies on symbionts of many groups of insects, pursued by numerous investigators, including Paul and Linda Baumann, Nancy Moran, Serap Aksoy, Roy Gross, who together investigated symbionts of aphids, tsetse flies, ants, leafhoppers, mealybugs, whiteflies, psyllids and others.
External links
- Comparative Analysis of Buchnera Genomes (at DOE'sUnited States Department of EnergyThe United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
IMG systemIntegrated Microbial Genomes SystemThe Integrated Microbial Genomes is a genome browsing and annotation system developed by the DOE-Joint Genome Institute. IMG contains all the draft and complete microbial genomes sequenced by the DOE-JGI integrated with other publicly available genomes...
)