Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Discovery reveals how bacteria distinguish harmful vs. helpful viruses

01.09.2014

When they are not busy attacking us, germs go after each other. But when viruses invade bacteria, it doesn't always spell disaster for the infected microbes: Sometimes viruses actually carry helpful genes that a bacterium can harness to, say, expand its diet or better attack its own hosts.

Scientists have assumed the bacterial version of an immune system would robotically destroy anything it recognized as invading viral genes. However, new experiments at Rockefeller University have now revealed that one variety of the bacterial immune system known as the CRISPR-Cas system can distinguish viral foe from friend. And, the researchers report in a paper published August 31 in Nature, it does so by watching for one particular cue.


Above, particles of the virus ΦNM1, applied at varying concentrations, killed cells in the Staphylococcus aureus "lawn," creating clear plaques. Researchers have shown Staph can detect whether a virus, such as ΦNM1, is destructive or potentially helpful.

Credit: Zach Veilleux/Rockefeller University

"Transcription — an initial step in the process that reads genes, including those of viruses — makes the difference," says researcher Luciano Marraffini, head of the Laboratory of Bacteriology. "The full genome of viruses in their lytic, or destructive phase, is transcribed. Meanwhile, a few of the genes from a virus are transcribed during its lysogenic, or dormant phase."

Viruses in their lytic phase make copies of themselves using a cell's machinery before destroying it to liberate these new viruses. Viruses in their lysogenic phase, meanwhile, quietly integrate into a host's genetic material. And this is where they offer their potential benefit to the bacteria, which co-opt viral genes for their own ends. In fact, some disease-causing microbes, such as the bacterium responsible for diphtheria, must pick up the right virus in order to attack humans.

Scientists have only discovered this adaptive bacterial immune system relatively recently. Its function relies on CRISPRs, sections of DNA that contain repeating sequences interspersed with unique sequences called spacers. (CRISPR stands for clustered regularly interspaced short palindromic repeats.) The spacer sequences match the sequences in the viral genetic code, making it possible for enzymes encoded by CRISPR-associated genes (Cas) to chop out single spacer sequences from the RNA transcribed from the CRISPR DNA. Other Cas enzymes then use these spacer sequences as guides to target invaders for destruction.

The system can adapt to new invaders by acquiring new spacer sequences to target them. Recently, CRISPR-Cas systems have attracted significant scientific attention because their ability to make precisely targeted cuts in DNA can be put to use to genetically engineer all types of cells.

"Our understanding of CRISPR-Cas systems remains in the early stages, but, so far, it has generally been thought they lack a sophisticated way of discriminating their targets. In other words, once they target something, it will be chopped up," says the study's lead author, graduate student Gregory Goldberg. "For the first time, our work has shown that a CRISPR-Cas system, one found in Staphylococcus bacteria, can detect whether or not a virus is in its destructive phase and poses an immediate threat."

Most previous work has focused on lytic viruses. However, Staphylococci host many viruses capable of entering a lysogenic phase. The researchers also uncovered a telling asymmetry in the Staphylococcal CRISPR system's ability to effectively target a sequence and its counterpart on two strands of complimentary DNA. They suspected this discrepancy arose because transcription proceeds in a single direction for most viral genes, meaning one of the two target strands is not transcribed.

"The big clue showed up when we isolated a mutant virus that managed to evade destruction. Sometimes viruses can do this through a mutation in a target sequence that prevents the system from identifying them. But when we sequenced the genome of this phage, we found a mutation in a region that promotes transcription instead," Goldberg says.

In a series of experiments, he and colleagues tested their hypothesis that the Staphylococcal CRISPR-Cas system, known as Type III-A, can tolerate an infection by a lysogenic virus, so long as the target sequences are not transcribed. They engineered a target sequence that would undergo transcription only in the presence of a specific chemical. As a result, the Type III-A CRISPR-Cas system only destroyed the target in the presence of this chemical.

"This discovery of a transcription requirement is likely to surprise many who work with these systems," Marraffini says. "Although we do not yet understand the mechanism behind it, we can say that the Type -III-A system is quite different from other CRISPR-Cas systems, of which there is a mysteriously large variety. Our discovery hints at the possibility that each CRISPR type and subtype recognizes and destroys its targets in different ways, each in tune with a particular bacterium's needs. If these different targeting mechanisms do exist, they could have important implications for biotechnology."

Zach Veilleux | Eurek Alert!
Further information:
http://www.rockefeller.edu

Further reports about: CRISPR DNA Discovery Rockefeller bacteria bacterial genes immune lysogenic lytic sequence sequences spacer transcription viruses

More articles from Life Sciences:

nachricht Fish Oil-Diet Benefits May be Mediated by Gut Microbes
28.08.2015 | University of Gothenburg

nachricht Bio-fabrication of Artificial Blood Vessels with Laser Light
28.08.2015 | Fraunhofer-Institut für Lasertechnik ILT

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: OU astrophysicist and collaborators find supermassive black holes in quasar nearest Earth

A University of Oklahoma astrophysicist and his Chinese collaborator have found two supermassive black holes in Markarian 231, the nearest quasar to Earth, using observations from NASA's Hubble Space Telescope.

The discovery of two supermassive black holes--one larger one and a second, smaller one--are evidence of a binary black hole and suggests that supermassive...

Im Focus: What would a tsunami in the Mediterranean look like?

A team of European researchers have developed a model to simulate the impact of tsunamis generated by earthquakes and applied it to the Eastern Mediterranean. The results show how tsunami waves could hit and inundate coastal areas in southern Italy and Greece. The study is published today (27 August) in Ocean Science, an open access journal of the European Geosciences Union (EGU).

Though not as frequent as in the Pacific and Indian oceans, tsunamis also occur in the Mediterranean, mainly due to earthquakes generated when the African...

Im Focus: Self-healing landscape: landslides after earthquake

In mountainous regions earthquakes often cause strong landslides, which can be exacerbated by heavy rain. However, after an initial increase, the frequency of these mass wasting events, often enormous and dangerous, declines, in fact independently of meteorological events and aftershocks.

These new findings are presented by a German-Franco-Japanese team of geoscientists in the current issue of the journal Geology, under the lead of the GFZ...

Im Focus: FIC Proteins Send Bacteria Into Hibernation

Bacteria do not cease to amaze us with their survival strategies. A research team from the University of Basel's Biozentrum has now discovered how bacteria enter a sleep mode using a so-called FIC toxin. In the current issue of “Cell Reports”, the scientists describe the mechanism of action and also explain why their discovery provides new insights into the evolution of pathogens.

For many poisons there are antidotes which neutralize their toxic effect. Toxin-antitoxin systems in bacteria work in a similar manner: As long as a cell...

Im Focus: Fraunhofer IPA develops prototype of intelligent care cart

It comes when called, bringing care utensils with it and recording how they are used: Fraunhofer IPA is developing an intelligent care cart that provides care staff with physical and informational support in their day-to-day work. The scientists at Fraunhofer IPA have now completed a first prototype. In doing so, they are continuing in their efforts to improve working conditions in the care sector and are developing solutions designed to address the challenges of demographic change.

Technical assistance systems can improve the difficult working conditions in residential nursing homes and hospitals by helping the staff in their work and...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Networking conference in Heidelberg for outstanding mathematicians and computer scientists

20.08.2015 | Event News

Scientists meet in Münster for the world’s largest Chitin und Chitosan Conference

20.08.2015 | Event News

Large agribusiness management strategies

19.08.2015 | Event News

 
Latest News

Interstellar seeds could create oases of life

28.08.2015 | Physics and Astronomy

An ounce of prevention: Research advances on 'scourge' of transplant wards

28.08.2015 | Health and Medicine

Fish Oil-Diet Benefits May be Mediated by Gut Microbes

28.08.2015 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>