Buchnera (bacterium) - Wikipedia
of how might relationships like aphids and Buchnera be maintained and evolved. View Test Prep - QUIZ 9 and 10 from ENT at Pennsylvania State University. QUIZ 9 What do aphids get from a symbiotic relationship with Buchnera? 9. When we injected diverse aphid strains, which harbored only Buchnera, with We have added another endosymbiont relationship that potentially affects a host .
Analysis of 16s rRNAs from Buchnera have shown that they belong to the gamma-3 subgroup of Proteobacteria, and are related with the Enterobacteriaceae family . They have extremely small genomes and lack genes for many extracellular structures or metabolic pathways found in other closely related bacteria . Other symbionts in aphids Besides Buchnera, other bacteria have also been found in aphids either living within bacteriocytes or not .
Among them include Wolbachia species and Hamiltonella defensa. The latter has be found to benefit their host by providing them protection against natural enemies . Microbial processes and activities Biosynthesis of essential amino acids Treatments of antibiotics on aphids have shown detrimental effects in development and reproduction, which could be complemented by supplementation of crucial amino acids in diets.
Together with findings showing retention of amino acids biosynthesis genes in the small Buchnera genome, it was concluded that Buchnera benefit their host mainly by producing essential amino acids  . Utilization of nutrients in the host Due to the genome reduction process during evolution, Buchnera have lost genes necessary to produce many nutrients . For example, in order to produce essential amino acids, the bacteria require nitrogenous substrate provided by their host.
These include nonessential amino acids such as serine, aspartate, glutamate, and glutamine. Genomic characteristics of Buchnera correspond to their unique lifestyle Unlike many microbes and pathogens living in animals, Buchnera do not harbor genes necessary for cell-surface components.
Genes involving lipopolysaccharide and phospholipid biosynthesis are lacking in Buchnera genomes.
Also, regulator and defense genes that are crucial for free-living bacteria are not found together making them unable to survive outside of their host. Such characteristics are crucial for this organism to establish symbiotic relationships with their hosts. Coevolution of aphids and Buchnera Given the interactions found between Buchnera with aphids, and significant genome reduction seen in the bacterial genome, it has been suggested that reciprocal selection between the two groups of organisms have resulted in coevolution of the mutualistic partnership .
Genomic revelations of a mutualism: the pea aphid and its obligate bacterial symbiont
The relationship have been predicted dating back million years ago, providing possible insights into the emergence of organelles in eukaryotic cells. Current Research Mechanisms leading to host-endosymbiont relationships Endosymbionts escaping out of weevil bacteriocytes after RNAi targeting antimicrobial peptide genes. Science Clues in how host-endosymbiont interaction evolved have been found in recent expression studies of insect transcriptomes, many of which point toward the regulation of insect host defenses.
In a recent study, RNAi targeting antimicrobial peptide genes have shown to disrupt the mutualistic relationship of weevils and their endosymbionts within bacteriocytes .
Such discoveries provided insights of how might relationships like aphids and Buchnera be maintained and evolved. Discovery of other endosymbionts Since the first genome study of Buchnera sequencing technologies have continued to improve dramatically. Endosymbionts similar to Buchnera are thus being discovered or sequenced in many other animals, some of which showing more extreme adaptations toward symbiotic lifestyles.
For example, the endosymbiont Carsonella rudii found in Pachpsylla venusta, was shown to have a genome size as small as kilobases . Evolution of organelles Obligate endosymbiont like Buchnera share various characteristics with organelles found in eukaryotes .
Aphids and Buchnera - microbewiki
Unique relationships of these endosymbionts with hosts have been served as important models in understanding the evolution process of endosymbiosis and eventually the origin of organelles .
Aphids are plant pests, capable of causing major agricultural damage. They feed on plants by piercing them with syringe-like mouth parts and sucking the sap out of the phloem, resulting in a diet that is rich in carbohydrates and deficient in amino acids. Some of these amino acids cannot be synthesized by the insect but are supplied by the intracellular symbionts Buchnera aphidicola. The interaction of the two partners dates back to million years and both have become so dependent on each other that under natural conditions they cannot exist without each other.
The Symbionts Supply the Host with Essential Amino Acids Because plant sap contains little protein and aphids cannot produce ten amino acids called essential amino acidsit was thought that if the aphids feed exclusively on plants then the required amino acids must come from their symbiotic bacteria. This hypthesis was investigated using several different approaches. On a growth medium without amino acids, aphids can grow and reproduce. However, if an antibiotic that kills bacteria is added to the medium, the aphids fail to grow and reproduce.
This suggests that bacterial symbionts are essential in supplying the amino acids. This was further supported using labelled sulfur or nitrogen compounds that showed amino acids containing these labels appearing in the symbionts and being provided to the host. The symbionts genome also reflects this biosynthetic activity.
Buchnera aphidicola, the symbiont of Schizaphis graminum, carries on a plasmid the two genes trpEG which are important in tryptophan synthesis. Each bacterium contains three or four plasmids that contain four tandem repeats of these genes, resulting in 12 to 16 copies of trpEG. The Host Supplies Symbiont Nutrients The intracellular location of the symbionts requires that the host supplies the bacteria with energy, carbon, and nitrogen. One amino acid, gluatmine, is very abundant in the phloem.
It was shown that glutamine is ingested by the aphid and transported to the cells in which the symbionts are housed bacteriocytes. The bacteriocytes take up glutamine, convert it to glutamic acid, that in turn is taken up by the bacterial symbiont.
The nitrogen from glutamic acid is then used to synthesize the other amino acids which are ultimately utilized by the host animal. This cycling of amino acids permits the growth and reproduction of aphids. Location of the symbionts The symbionts are found inside host cells intracellular that are called bacteriocytes also called mycetocytes.
Each symbiont is surrounded by a membrane derived from the host cell that forms a vesicle called the symbiosome. The amino acids produced by the bacterial symbiont are thought to be released and taken up by the host cells.
Digestion or destruction of the symbionts does not usually occur except during specific developmental stages. Being intracellular symbionts, the bacteria rely on the host to ensure transmission to the next generation. In several aspects, these intracellular bacteria resemble cellular organelles. The study of this system, as well as other symbioses with intracellular symbionts, may aid in understanding how mitochondria and plastids became an integral part of eukaryotic cells.
Genome sequence of the symbiont The sequence of the symbiont's genome was determined. Its analysis revealed that bacteria carried the genes required for the biosynthesis of amino acids that the host could not synthesize but lacked the genes needed for the biosynthesis of non-essential amino acids. The symbiont also lacked many other genes that are commonly found in free-living or facultative intracellular bacteria. This suggests that the symbionts and host have coevolved to such an extend that they can only live in each others presence.
The availability of the sequence will enable researchers to address a wide range of questions using powerful genomic approaches.