Skip to main content

To curb infection, bacteria direct their defenses against themselves!!

Sometimes, the best defense against hostile invaders is a good, long nap. Or at least, that strategy seems to work for bacteria.
In a new study, described in Nature, Rockefeller scientists showed that microbes under viral attack turn their defenses not only on their enemies, but also on themselves. This drastic measure, the researchers found, doesn't kill the bacteria, but rather sends them into a dormant state that prevents the infection from spreading.
Vicious viruses
Among bacteria, viruses called bacteriophages are public enemy number one.
These pathogens propagate by injecting their genome into unsuspecting microbes, eventually causing their host cell to rupture, at which point progeny phage is released to infect other members of a bacterial colony.
To mitigate these attacks, bacteria have evolved immune mechanisms known as CRISPRs, or clustered regularly interspaced short palindromic repeats, which, with the help of associated Cas enzymes, detect and destroy foreign genetic material.
Microbes have at their disposal many different CRISPR systems, one of which caught the attention of Luciano Marraffini due to its unique strategy for fending off intruders. Whereas most Cas enzymes destroy viral DNA, this particular enzyme, Cas13, works by cleaving RNA.
"Since Cas13 targets RNA, it was initially thought to have evolved to impede phages with RNA genomes. The problem is, RNA phages exceedingly rare," he says. "So we wanted to see whether it might have evolved to serve a different function."
Working with Helen Hay Whitney postdoctoral associate Alexander Meeske, Marraffini showed that activation of Cas13 actually protects bacteria from phages with DNA genomes, which are far more common. But how, they wondered, could an RNA-cutting enzyme actually defend microbes from this kind of virus?
Through a series of experiments, the researchers found that Cas13 helps bacteria, ironically, by hindering them. That is, the enzyme cuts up bits of host RNA, sending the bacteria into a dormant state -- a kind resting phase in which the microbes remain alive but don't grow. This strategy works, says Meeske, because viruses need host RNA to replicate.
"Phages are parasites: They don't have all the elements needed for their propagation, so they rely on the host," he explains. "And if the host cell isn't making those elements, the phage cannot propagate."
No escape
The researchers also found that Cas13 kills viruses more thoroughly than other Cas enzymes. Standard CRISPR-Cas systems are highly specific, cutting up bits of DNA that match a precise genetic sequence. And while this specificity can be an asset, it also comes with a big drawback: If a virus mutates, CRISPR cannot recognize the invader, and the phage escapes scot-free.
"If a phage has a single point mutation in its target sequence, then usually the virus is invisible to Cas and the infection will succeed," says Marraffini. "But with Cas13 we didn't see any escaper mutants."
The researchers attribute this superb virus-fighting power to the fact that cell dormancy does not target one particular virus, but rather makes it impossible for any phage -- including mutants -- to propagate. And while an indefinite nap may not seem like much of a life for a microbe, Meeske notes that the real benefit of Cas13 lies not at the level of the individual, but of the bacterial community as a whole.
"The phage has one shot to deliver its genetic payload and replicate," he says. "So if they inject their genome into a host that turns out to be inhospitable, the infection stops there. The phage loses, and the bacterial colony wins."
Story Source:
Materials provided by Rockefeller University. 
Note: Content may be edited.

Comments

Post a Comment

Popular posts from this blog

Size matters: New data reveals cell size sparks genome awakening in embryos

Transitions are a hallmark of life. When dormant plants flower in the spring or when a young adult strikes out on their own, there is a shift in control. Similarly, there is a transition during early development when an embryo undergoes biochemical changes, switching from being controlled by maternal molecules to being governed by its own genome. For the first time, a team from the Perelman School of Medicine at the University of Pennsylvania found in an embryo that activation of its genome does not happen all at once, instead it follows a specific pattern controlled primarily by the various sizes of its cells. The researchers published their results this week as the cover story in  Developmental Cell . In an early embryo undergoing cell division, maternally loaded RNA and proteins regulate the cell cycle. The genomes of the zygote -- a term for the fertilized egg -- are initially in sleep mode. However, at a point in the early life of the embryo, these zygotic nuclei "wake...
Post a Comment
Read more

Home births as safe as hospital births: International study suggests

A large international study led by McMaster University shows that low risk pregnant women who intend to give birth at home have no increased chance of the baby's perinatal or neonatal death compared to other low risk women who intend to give birth in a hospital. The results have been published by  The Lancet 's  EClinicalMedicine  journal. "More women in well-resourced countries are choosing birth at home, but concerns have persisted about their safety," said Eileen Hutton, professor emeritus of obstetrics and gynecology at McMaster, founding director of the McMaster Midwifery Research Centre and first author of the paper. "This research clearly demonstrates the risk is no different when the birth is intended to be at home or in hospital." The study examined the safety of place of birth by reporting on the risk of death at the time of birth or within the first four weeks, and found no clinically important or statistically different risk between home...
Post a Comment
Read more

Molecular adlayer produced by dissolving water-insoluble nanographene in water

Molecular adlayer produced by dissolving water-insoluble nanographene in water : "Nanographene incorporated micelle capsules" can be prepared by simply pulverizing and mixing nanographene with amphiphilic V-shaped anthracene molecules in water at room temperature. Even though nanographene is insoluble in water and organic solvents, Kumamoto University (KU) and Tokyo Institute of Technology (Tokyo Tech) researchers have found a way to dissolve it in water. Using "molecular containers" that encapsulate water-insoluble molecules, the researchers developed a formation procedure for a nanographene adlayer, a layer that chemically interacts with the underlying substance, by just mixing the molecular containers and nanographene together in water. The method is expected to be useful for the fabrication and analysis of next-generation functional nanomaterials. Graphene is a single layer of carbon atoms arranged in sheet form. It is lighter than metal wit...
Post a Comment
Read more