UM researchers discover a “simple and elegant mechanism” that regulates relationships between insects and bacteria.
Symbiosis is the process that occurs when two different organisms live together to form a mutually beneficial partnership. In many symbiotic relationships, host animals and their microbial symbionts are partners that make up a whole – neither one can function without the other but together they grow and reproduce.
Adult pea aphid
A study by University of Miami researchers reveals how, at the cellular level, an animal and its symbiotic bacteria work together to make up a single organismal system. The study titled “Aphid amino acid transporter regulates glutamine supply to intracellular bacterial symbionts” is published in the journal Proceedings of the National Academy of Science (PNAS).
The findings show how a simple mechanism allows an insect, the pea aphid, to regulate the manufacturing of essential nutrients supplied by its symbiotic bacteria called Buchnera aphidicola.
“We’ve identified the key regulator of this symbiosis,” said Alex C. C. Wilson, associate professor of Biology in the College of Arts and Sciences and corresponding author of the study. “It’s our first real insight into the mechanisms working at the interface of the host and symbiont.”
The pea aphid feeds on plant sap. Its diet is deficient in essential nutrients called amino acids. The aphid can produce some amino acids on its own, but the rest it must get from beneficial bacteria that live inside aphid cells. In turn, the symbiotic bacteria can’t produce amino acids that the aphid can make, so the partners exchange insect-produced amino acids for symbiont-produced amino acids.
“That conversion of going from a diet with an inappropriate nutritional profile, to an appropriate profile occurs in collaboration between the bacteria and the host,” Wilson said. “The question is whether the production of nutrients changes with supply and demand and if so, how it happens.”
To help answer this question the researchers looked at amino acids that are fundamental to the pea aphid-Buchnera symbiotic function. One of those amino acids is glutamine, which is made in the aphid. Glutamine is important because it’s the precursor for all amino acids produced both by the aphid and by the symbiont. The other amino acid is arginine, which is made in Buchnera and it’s deficient in the pea aphid’s diet.
Glutamine is ferried across a membrane that surrounds the cells where the bacteria lives, by an amino acid transporter named ApGLNT1. To study this transport mechanism the researchers used a procedure that uses frog eggs (called oocytes) to manufacture ApGLNT1. This specialized approach is used by Charles W. Luetje, chairman of the department of Molecular and Cellular Pharmacology in the UM Miller School of Medicine and co-author of the study.
“My lab specializes in the use of a technique that allows functional studies of various receptors, channels and transporters,” said Luetje. “The oocytes are useful for expression of a wide variety of proteins and are particularly helpful when studying difficult proteins that don’t express well in other systems.”
Based on their work figuring out what ApGLNT1 transports and where it is localized in the pea aphid, the researchers built a model that describes how the amino acid factory responds to supply and demand.
The findings show that when there is a buildup of arginine in the pea aphid, arginine binds to ApGLNT1, and inhibits glutamine uptake. Since glutamine is a precursor for amino acids, the bacteria’s synthesis of arginine is in turn reduced. Once arginine is assimilated by the host, glutamine transport resumes and synthesis of arginine is restored.
“To our surprise, the transporter is a key regulator of the factory production line,” said Daniel R. G. Price, who worked on the project when he was assistant scientist in the Department of Biology at UM and is first author of the study.
“When aphid demand for essential nutrients is high, the transporter imports large amounts of precursor and the precursor is converted into essential nutrients that are returned to the aphid,” Price says. “Conversely, when there is low aphid essential nutrient demand, little precursor is imported and the essential nutrient production factory is shut down.”
A remarkably basic mechanism regulates the biosynthesis of symbiont-produced arginine, in response to the needs of the pea aphid. But the model goes further than that.
“Since ApGLNT1 localizes to the membrane of aphid cells where the bacteria resides and because of other features peculiar to aphid metabolism, transporter ApGLNT1 not only regulates arginine biosynthesis, but all amino acid biosynthesis,” Wilson said. “The system is simple and elegant.”
Thus amino acid transporters play a key role in the evolutionary success of these insects. But an important question remains: How generalizable is this regulatory mechanism across symbiotic systems? Wilson’s lab may find the answer by looking at other sap-feeding insects with intracellular bacteria, based on an understanding that emerged from another study from her lab. The study titled “Dynamic recruitment of amino acid transporters to the insect-symbiont interface” is published in the journal of Molecular Ecology.
That study found that the presence of amino acid transporters is significantly expanded in some sap-feeding insects relative to non sap-feeding insects. Further, these expansions result from large-scale gene duplications that took place independently in different sap-eating insects. Gene duplication is a process that occurs when part of an organism’s genetic material is replicated. Groups of similar genes that share an evolutionary ancestry are called gene families.
“Given the extensive gene duplication of the amino acid transporter gene families that took place multiple times independently in sap-feeding insects, it makes sense that gene duplication might be important for recruiting amino acid transporters to mediate amino acid exchange between these insects and their symbionts,” said Rebecca P. Duncan, doctoral student in the Department of Biology at UM and first author of the study.
The sap-eating insects with expanded amino acid transporters come from a common ancestor. However, given that the genes expanded independently in each insect, sap-feeding insects likely evolved their relationships with their symbionts separately, as opposed to in their common ancestor. Hence, Wilson’s lab can test if their model is broadly applicable by examining the mechanism of symbiotic regulation in the other sap-feeding insects used in this study. The findings of these studies show that symbiotic relationships have the power to shape animal evolution at the genetic level.
Annette Gallagher | Eurek Alert!
Dune ecosystem modelling
26.06.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau
Understanding animal social networks can aid wildlife conservation
23.06.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
26.06.2017 | Life Sciences
26.06.2017 | Physics and Astronomy
26.06.2017 | Information Technology