Navigation Links
Some bacteria attack using spring-loaded poison daggers

PASADENA, Calif.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. 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 workby shooting spring-loaded poison molecular daggers.

"People aren't surprised that animals have really interesting ways to hurt each othersnakes 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-weaponwhich spans a distance no longer than about 80 atoms lined up end-to-endis 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 cryomicroscopean electron microscope that enables researchers to observe samples in a near-native stateto image an environmental strain of Vibrio cholerae cells. Unlike traditional electron microscopyfor which samples must be fixed, dehydrated, embedded in plastic, sectioned, and stainedelectron 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 videosso-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 conformationsextended 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."


Contact: Deborah Williams-Hedges
California Institute of Technology

Related biology news :

1. Disinfectants can make bacteria resistant to treatment
2. H. Pylori bacteria may help prevent some esophageal cancers
3. Scientists discover bacteria that can cause bone infections
4. Waste from gut bacteria helps host control weight, UT Southwestern researchers report
5. Gene against bacterial attack unravelled
6. Predatory bacterial swarm uses rippling motion to reach prey
7. Bacteria manage perfume oil production from grass
8. Nature study demonstrates that bacterial clotting depends on clustering
9. Battling bacteria in the blood: Researchers tackle deadly infections
10. Shifts in soil bacterial populations linked to wetland restoration success
11. New bacteria discovered in raw milk
Post Your Comments:
Related Image:
Some bacteria attack using spring-loaded poison daggers
(Date:11/19/2015)...  Although some 350 companies are actively involved in ... companies, according to Kalorama Information. These include Roche Diagnostics, Hologic, ... share of the 6.1 billion-dollar molecular testing market, according ... Molecular Diagnostic s .    ... by one company and only a handful of companies ...
(Date:11/17/2015)... , November 17, 2015 Paris ...   --> Paris from 17 th ... DERMALOG, the biometrics innovation leader, has invented the first combined ... on the same scanning surface. Until now two different scanners ... one scanner can capture both on the same surface. ...
(Date:11/17/2015)... Nov. 17, 2015 Pressure BioSciences, Inc. (OTCQB: ... development and sale of broadly enabling, pressure cycling technology ... industry, today announced it has received gross proceeds of ... Private Placement (the "Offering"), increasing the total amount raised ... more additional closings are expected in the near future. ...
Breaking Biology News(10 mins):
(Date:11/25/2015)... ANGELES and HOLLISTON, Mass. ... Technology, Inc. (Nasdaq: HART ), a biotechnology company ... that CEO Jim McGorry will present at ... December 1, 2015 at 2:30 p.m. PT. The presentation ... below) for 30 days. Management will also be available ...
(Date:11/25/2015)... , ... November 25, 2015 , ... ... the Organization of Black Aerospace Professionals (OPBAP) has been formalized with the signing ... AMA team leaders met with OPBAP leaders Capt. Karl Minter and Capt. Albert ...
(Date:11/25/2015)... ... November 25, 2015 , ... ... featured on AngelList early in their initial angel funding process. Now, they are ... individuals looking to make early stage investments in the microbiome space. In ...
(Date:11/24/2015)... SUNNYVALE, Calif. , Nov. 24, 2015 ... executives will be speaking at the following conference, and ... New York, NY      Tuesday, December 1, ... New York, NY      Tuesday, December 1, ...      Piper Jaffray Healthcare Conference, New York, NY ...
Breaking Biology Technology: