Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Some bacteria attack using spring-loaded poison daggers

27.02.2012
Bacteria have evolved different systems for secreting proteins into the fluid around them or into other cells.

Some, for example, have syringe-like exterior structures that can pierce other cells and inject proteins. Another system, called a type VI secretion system, is found in about a quarter of all bacteria with two membranes.


A team, co-led by researchers at the California Institute of Technology, has figured out the structure of the type VI secretion system apparatus and proposed how it might work -- by shooting spring-loaded poison molecular daggers. Credit: Nature/Everett Kane

Despite being common, researchers have not understood how it works. Now a team, co-led by researchers at the California Institute of Technology (Caltech), has figured out the structure of the type VI secretion system apparatus and proposed how it might work—by shooting spring-loaded poison molecular daggers.

"People aren't surprised that animals have really interesting ways to hurt each other—snakes have venom, bears have claws," says Grant Jensen, professor of biology at Caltech and coleader of the study. "But they might be surprised that a single cell within one of those animals' bodies is still 100 times larger than the bacterial cells we're talking about, and yet the bacterial cells contain weapons that are so sophisticated. That's the marvel."

The nano-weapon—which spans a distance no longer than about 80 atoms lined up end-to-end—is a tube that contracts very quickly, firing an inner dagger through the cell's membranes, into the surrounding medium and, possibly, into another cell. The tube then disassembles and can reassemble elsewhere in the cell, ready to fire another molecular dagger.

The findings, made in collaboration with researchers at Harvard Medical School, appear as an advance online publication of the journal Nature.

The work began with an accidental discovery. Researchers in the Jensen lab were using an electron cryomicroscope—an electron microscope that enables researchers to observe samples in a near-native state—to image an environmental strain of Vibrio cholerae cells. Unlike traditional electron microscopy—for which samples must be fixed, dehydrated, embedded in plastic, sectioned, and stained—electron cryotomography (ECT) involves freezing samples so quickly that they become trapped within a layer of transparent, glasslike ice. The microscope can then capture high-resolution images as the sample is rotated, and those images can be stitched together to make 3D videos—so-called tomograms.

Jensen and his team wanted to use the technique to observe how V. cholerae cells segregate two duplicate copies of their genetic material before dividing. Instead, they noticed relatively large tubelike structures spanning the entire width of the cells. And they had no idea what the structures were.

Jensen started sharing preliminary images of the mysterious structures in lectures around the country, asking if anyone knew what they might be. Finally, someone suggested that he talk to John Mekalanos of Harvard Medical School, who was involved in the original discovery of the type VI secretion system. After Martin Pilhofer, a postdoctoral scholar in Jensen's lab, comprehensively imaged the system and conducted additional investigations, Mekalanos's group became convinced that the tubelike structures might actually help the bacteria translocate proteins.

The Mekalanos lab made a version of V. cholerae lacking one of the proteins that makes up the tube structure. With that protein knocked out, the type VI secretion system disappeared. In another experiment, they attached fluorescent tags to the proteins and were actually able to watch the structures form and contract within living cells.

"When the tube contracts, that's when it shoots," says Pilhofer. "That result agrees well with what we had seen using the electron cryomicroscope, where we observed long tubular structures in two different conformations—extended and contracted. Whereas electron cryomicroscopy allowed us to observe the secretion apparatus at high resolution, the fluorescence study gave us more insight into the dynamics of the system."

The firing mechanism is similar to the one used by bacteriophages, viruses that infect bacteria. Phage tails are made up of an outer sheath and an inner tube that gets ejected. Since other researchers had previously established that proteins in the type VI secretion system are similar to those found in various parts of the phage tail and its associated structures, there is even more support for the newly discovered mechanism for the type VI secretion system.

"These amazing tubes inside the cell went undetected for decades of traditional electron microscopy, and they may have stayed that way for many more," says Jensen, who is also an HHMI investigator. "But Caltech made a wise investment a long time ago, with the generous help of the Gordon and Betty Moore Foundation, into our one-of-a-kind electron cryomicroscope, and it is truly what allowed us to see these structures."

In addition to Jensen, Pilhofer, and Mekalanos, other authors on the Nature paper, "Type VI secretion requires a dynamic contractile phage tail-like structure," include Gregory Henderson, a former graduate student in Jensen's lab who is now a resident physician at the Mayo Clinic, and Marek Basler, a postdoctoral scholar at Harvard Medical School. The work was supported by grants from the National Institute of Allergy and Infectious Diseases and the National Institute of General Medical Sciences.

Deborah Williams-Hedges | EurekAlert!
Further information:
http://www.caltech.edu

More articles from Life Sciences:

nachricht Warming ponds could accelerate climate change
21.02.2017 | University of Exeter

nachricht An alternative to opioids? Compound from marine snail is potent pain reliever
21.02.2017 | University of Utah

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Impacts of mass coral die-off on Indian Ocean reefs revealed

21.02.2017 | Earth Sciences

Novel breast tomosynthesis technique reduces screening recall rate

21.02.2017 | Medical Engineering

Use your Voice – and Smart Homes will “LISTEN”

21.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>