Buchnera - Aphids
In doing so, we address four issues central to understanding the patterns and processes The aphid/Buchnera symbiosis is primarily a nutritional symbiosis. In addition to providing nutrients, this obligate symbiosis is crucial for aphid development and reproduction (Sasaki et al., ; Douglas, ; Hardie and. one of the fundamental questions in biology: How did the eukaryotic cell evolve ? It even occurs in an aphid species that once had a Buchnera But this process is not observed in males of another aphid species Developmental Origin and Evolution of Bacteriocytes in the Aphid–Buchnera Symbiosis.
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.
Genomic revelations of a mutualism: the pea aphid and its obligate bacterial symbiont
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.
Aphid-bacterial symbioses | The Godfray Lab
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. Evolution of bacterial symbionts and aphids The association between Buchnera and aphids is a mutualism, which was probably established to million years ago. At that time, an ancestor of Buchnera infected an aphid ancestor.
An important aspect in the evolution of this symbiosis is the vertical transmission of the symbionts from parent to offspringindicating coevolution of the bacteria and host. This coevolution is apparent in the similarity between the branching patterns of the aphid phylogenetic tree and those of the symbionts.
Investigators Paul Baumann's group University of California, Davis identified the bacterial symbiont using 16S rRNA gene sequences and used molecular techniques to isolate genes and plasmids from the symbiont. These techniques are essential in studying this system because the symbionts cannot be cultured outside the host. A better understanding of the mechanisms of wing development in aphids will provide new insights in the long term sustainable management of this key insect pest of wheat.
The aphid colony was generated from a single wingless adult female. The offspring from this single clone was reared in 9 cm diameter Petri dishes individually. After three generations, aphids were subjected to the subsequent experiments.
The neonatal nymphs are sensitive to environmental cues associated with wing development. In contrast, only a single nymph was kept in the Petri dishes to generate wingless morph. Selective elimination of primary endosymbionts was obtained as described below. Rifampicin Treatment The 24 h postnatal nymphs were maintained on artificial diets Chen et al.
This treatment has been used to eliminate aphid-Buchnera endosymbiotic bacteria with minimal deleterious effects on the aphid itself Adams and Douglas, The control aphids were maintained on regular artificial diets for 48 h. The status of Buchnera in aphid samples was assessed by PCR. Total DNAs were isolated from natural symbiotic control; non-rifampicin treated and rifampicin treated individuals using E. Phenotypic Impacts of Antibiotic Treatment Rifampicin treated and symbiotic control aphids were transferred to wheat seedlings, with 20 nymphs per plant.
A total of five replicates were carried out for each experiment. Before the experiment, the number of winged and wingless morphs was counted, and these aphids were considered the F1 population namely WG-1 and WLG These adults were allowed to reproduce for 3 days. When their offspring developed into the fourth-instar nymphs or adults, the number of winged and wingless morphs were counted again, and this generation of aphids was defined as F2 population namely WG-2 and WLG Phenotypic Impacts of Starvation The phenotypic impacts of starvation on wing development were assayed using first and second instar nymphs.
Nymphs were maintained on Petri dishes for 0, 24, 48, and 72 h without food before returning to wheat seedlings. The survival rate of nymphs were documented at time points 0, 24, and 48 h after treatment. When nymphs reached the adult stage, the number of winged and wingless morphs was counted, including both F1 and F2 populations.
The end point measurements included the survival rate and the percentage of winged morphs. Results Establishment of Rifampicin-Cured Aphid Lines To verify the elimination of Buchnera after antibiotic treatment, we isolated DNAs from both symbiotic and rifampicin-cured aphids, respectively.
Gel electrophoresis analysis showed that the DNAs extracted from both morphs were intact Figure 1Lanes 2 and 3however, Buchnera was absent from rifampicin-cured aphids Figure 1Lane 5 compared to symbiotic controls Figure 1Lane 4. Electrophoretic detection of Buchnera among symbiotic and cured aphids.
DNA of symbiotic aphids; Lane 3: DNA of rifampicin-cured aphids; Lane 4: PCR amplification of Buchnera in symbiotic aphids; Lane 5: PCR amplification of Buchnera in rifampicin-cured aphids.
Phenotypic Impact of Antibiotics Treatment on the Wing Development F1 Generation The overall percentage of winged morphs was reduced in rifampicin treated aphids compared to the untreated controls Figure 2A.
These percentages of winged aphids were decreased to 5. Elimination of Buchnera from neonatal nymphs significantly reduced subsequent fecundity in aphids compared to control groups Figure 2B.
The number of offspring is These numbers dropped to Phenotypic impacts of rifampicin treatment on S. F2 Generation The percentage of winged morphs was also reduced in the F2 generation among rifampicin-treated aphids compared to the untreated controls Figure 2C.Endosymbiosis - Wikipedia audio article
These percentages dropped to The proportion of a red colored morph was not significantly different between WG-2 Morphological changes of adult S. A a wingless adult; B an intermediate form which should have developed into a winged morph but, instead, retained the sclerotized thorax and wing remnants arrow ; C a winged adult. Between Generations The percentage of winged morphs between generations exhibited a different trend. Specifically, the percentage of winged morphs was 5.
Moreover, there were no significant differences in the development of wing dimorphism between the generations WG-1 vs. Phenotypic Impact of Starvation on the Wing Development Both survival rate and the percentage of winged morphs were significantly reduced after starvation treatment to neonatal nymphs Figures 4A,B.
The survival rate decreased dramatically to 1.
Aphids and Buchnera
Consequently, wing development was further investigated only for aphids starved 0, 24, and 48 h. Phenotypic impacts of starvation treatment on S. The endpoint measurements include A Survivorship; B wing development; and production of F1 and winged individuals among F2 offspring from winged C and wingless D adults.
Starvation significantly reduced the percentage of the winged morphs in F1 S. Specifically, the percentage of winged aphids was drastically reduced from However, the percentage of winged morphs in WLG-1 was reduced from Among the three different starvation times, there were no significant differences in the wing development between WG-1 and WLG-1 0 h: The number of offspring and proportion of the winged individuals derived from the winged and wingless adults.
The starvation to neonatal nymphs affected aphid fecundity in comparison to the non-starved controls. Specifically, the number of offspring produced for the WG-2 generated increased from The opposite effect was shown in a decrease of WLG-2 offspring from This change in reproduction number of offspring across time 0 vs.
There were no significant differences in the percentage of winged individuals between controls and 24 h starvation treatments in WLG Discussion Symbiotic relationships with intracellular bacteria, such as Wolbachia and Buchnera, are pronounced across Insecta, and have evolved intricate interdependencies for mutual survival and propagation Baumann et al.
Many insect endosymbionts have crucial roles in host survival, whereby removal of these symbionts often results in notable fitness costs. Previous studies on Buchnera, the primary symbionts of sap-feeding insects, has revealed several effects on host insect fitness, development and reproduction Sasaki et al. Furthermore, detailed information available indicated the impact of aposymbionts on the performance, nutrition, metabolism, and feeding behavior of aphid Prosser and Douglas, ; Wilkinson and Douglas, Moran and Yun found that aphids with Buchnera replacement exhibited a dramatic increase in their heat tolerance.
Genomic revelations of a mutualism: the pea aphid and its obligate bacterial symbiont
This relationship with Buchnera is essential for compensation of nutritional deficiencies in plant phloem encountered by sap-feeding insects, and forms the basis of this mutualism.
Thus aphids, through the mutualistic association with Buchnera symbionts have attained the capacity to utilize phloem sap as the sole dietary source throughout their lifecycle Sasaki et al. Analysis and annotation of the Buchnera genome predicted the presence of most genes involved in the biosynthesis of essential amino acids and may lack certain cell wall lipid biosynthetic pathways Shigenobu et al.