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.
Among bacteria, viruses called bacteriophages are public enemy number one.
Pathogens - Genome - Microbes - Host - Cell
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 - Disposal - CRISPR - Systems - Attention
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."
Helen - Hay - Whitney - Associate - Alexander
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,...
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