Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Microbial resident enables beetles to feed on a leafy diet

17.11.2017

Thistle tortoise beetles outsource the job of breaking down plant cell walls to a symbiotic bacterium. It provides the beetle with the enzymes required to break down certain plant cell wall components. The genome of the bacterium is the smallest ever sequenced of any organism living outside a host cell. It contains genes that are responsible for the production of pectinases, the enzymes that break down pectin, an essential component of the plant cell wall. The production of pectinases is therefore the primary function of these bacteria. Without bacterial symbionts the beetles could not to gain access to the nutrients inside the plant cells and hence would be unable to survive

An international team including researchers from the Max Planck Institute for Chemical Ecology has described a bacterium residing in a species of leaf beetles which has an unexpected feature: it provides the beetle with the enzymes required to break down certain plant cell wall components. The genome of the bacterium is the smallest ever sequenced of any organism living outside a host cell.


Fluorescence in situ hybridization (FISH): The cross-section shows the symbiotic organs associated with the gut of the beetle. In these sac-like reservoirs, the symbiotic bacteria (green) are housed.

Benjamin Weiss / Mainz University; Hassan Salem / Emory University


The thistle tortoise beetle (Cassida rubiginosa) feeds on thistle leaves. Its favorite food plant is the field thistle, a dreaded weed in agriculture worldwide.

Hassan Salem / Emory University

It contains genes that are responsible for the production of pectinases, the enzymes that break down pectin, an essential component of the plant cell wall. The production of pectinases is therefore the primary function of these bacteria. Without bacterial symbionts the beetles could not to gain access to the nutrients inside the plant cells and hence would be unable to survive (Cell, November 2017, doi 10.1016/j.cell.2017.10.029).

„The bedrock of our study were the histological descriptions and drawings of the beetle’s symbiotic organs that were first published by the German zoologist Hans-Jürgen Stammer more than 80 years ago. We wanted to molecularly characterize the extraordinary partnership between a leaf beetle and its symbionts described by Stammer as a rare peculiarity,” first author Hassan Salem, formerly a doctoral student at the Max Planck Institute for Chemical Ecology, explains. He is currently a Feodor Lynen Postdoctoral Fellow of the Alexander von Humboldt Foundation at Emory University in Atlanta, Georgia, USA.

Hans-Jürgen Stammer (1899-1968) studied symbiotic partnerships between insects and bacteria during the 1920s and 30s. He found that leaf beetles (Chrysomelidae) are notorious for not partaking in symbiotic partnerships. However, his studies also revealed that there were exceptions to this finding among some tortoise beetle species, such as the thistle tortoise beetle (Cassida rubiginosa). These tortoise beetles are equipped with unusual organs, which he described in a 1936 study.

The symbiotic bacteria reside in sac-like reservoirs in the guts of the beetles. Female beetles transfer the symbionts through vaginal tubes to their offspring by applying a tiny symbiont caplet to each egg. The hatching larvae eat through the egg shell and then consume the caplets containing the symbiotic bacteria.

Leaf beetles are able to degrade components of the plant cell wall, such as cellulose and pectin, with the help of digestive enzymes. However, genetic analysis showed that the thistle tortoise beetle lacks the genes that are responsible for the production of the respective enzymes (pectinases). The new study reveals that this deficit is compensated for by a close partnership with a bacterium that resides in special organs close to the beetle’s gut.

To understand the importance of the bacterial symbionts for the beetle, the authors conducted a range of bioassays, some that were combined with enzymatic measurements. “When we compared enzyme activity in tortoise beetles with and without symbiotic bacteria, we found that beetles without symbionts were not able to digest pectin in order to gain access to the nutrients in the cell and as a consequence their chances of survival decreased,” says Roy Kirsch from the Max Planck Institute for Chemical Ecology.

Genetic analysis of the symbiotic bacteria ̶ which the researchers present as “Candidatus Stammera capleta“ in their current study to honor Stammer’s observations ̶ uncovered another surprise: The genome of the microorganism is reduced to only a few hundred genes, among them some genes that regulate the production and transport of pectinases.

Accordingly, the genome is tiny: Containing only ~270.000 base pairs, the genome of the bacterium is the smallest ever described for an organism that exists outside a host cell. Escherichia coli bacteria in comparison ̶ bacteria that live inside the gut of many animals including humans ̶ have 4.600.000, or 17 times as many base pairs. Only some bacteria that are housed inside their hosts’ cells are known to have smaller genomes than the beetle symbiont.

The symbiosis between the beetle and its symbiont is characterized by a clear division of labor. “The beetle host possesses the genes responsible for producing cellulases to digest cellulose, whereas the symbiont provides the pectinases. Together they have the necessary enzymes to break down the plant cell wall. Especially notable is the fact that this is the first description of a specialized bacterial symbiont with a primary or even sole function dedicated to pectin degradation,” Hassan Salem summarizes.

That many herbivorous animals exist today is the result of adaptations that evolved over time. In fact, microorganisms have played a major role in many such adaptations. The thistle tortoise beetle is an impressive example. Without pectinases it would have no access to nutrients inside a plant cell. The production of these enzymes has been outsourced to a service provider: a bacterium living in special organs near its gut.

In many leaf beetle species, the genes that activate digestive enzymes for the degradation of plant cell walls originated from fungi and bacteria and were introduced into the genomes of the beetles’ ancestors via horizontal gene transfer. “It is fascinating that insects have solved the problem of how to break up plant cell walls so differently. Why some insects acquired genes from microbes horizontally, while others maintain symbionts to do the same job is an interesting question that remains to be answered in future studies,” says Martin Kaltenpoth from the University of Mainz.

Original Publication:
Salem, H., Bauer, E., Kirsch, R., Berasategui, A., Cripps, M., Weiss, B., Kogy, R., Fukumori, K., Vogel, H., Fukatsu, T., Kaltenpoth, M. (2017). Drastic genome reduction in an herbivore's pectinolytic symbiont. Cell 172, DOI: 10.1016/j.cell.2017.10.029
https://doi.org/10.1016/j.cell.2017.10.029

Further Informationen:

Dr. Hassan Salem, Department of Biology, Emory University, Atlanta, GA 30312, USA, E-Mail hssalem@emory.edu

Prof. Dr. Martin Kaltenpoth, Johannes-Gutenberg-Universität Mainz, Johann-Joachim-Becher-Weg 13, 55128 Mainz, Tel. +49 6131 3924411, E-Mail mkaltenp@uni-mainz.de

Contact and Media Requests:
Angela Overmeyer M.A., Max Planck Institute for Chemical Ecology, Hans-Knöll-Str. 8, 07743 Jena, +49 3641 57-2110, E-Mail overmeyer@ice.mpg.de

Download of high resolution images via http://www.ice.mpg.de/ext/downloads2017.html

Angela Overmeyer | Max-Planck-Institut für chemische Ökologie

More articles from Life Sciences:

nachricht Stiffness matters
22.02.2018 | Albert-Ludwigs-Universität Freiburg im Breisgau

nachricht Separate brain systems cooperate during learning, study finds
22.02.2018 | Brown University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Developing reliable quantum computers

International research team makes important step on the path to solving certification problems

Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

Im Focus: Hybrid optics bring color imaging using ultrathin metalenses into focus

For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.

But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...

Im Focus: Stem cell divisions in the adult brain seen for the first time

Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.

The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Stiffness matters

22.02.2018 | Life Sciences

Magnetic field traces gas and dust swirling around supermassive black hole

22.02.2018 | Physics and Astronomy

First evidence of surprising ocean warming around Galápagos corals

22.02.2018 | Earth Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>