Scientists Increase Cas9-Based Bacterial Memories of Viruses by 100 Fold

Some microbes can form memories—although, inconveniently for scientists who study the process, they don’t do it very often. Rockefeller University researchers and colleagues at the University of California, Berkeley, have found a way to make bacteria encode memories much more frequently. Their discovery was published in the January 5, 2016 issue Molecular Cell. The article is titled “Mutations in Cas9 Enhance the Rate of Acquisition of Viral Spacer Sequences during the CRISPR-Cas Immune Response.” “CRISPR, the adaptive immune system found within many bacteria, remembers viruses by storing snippets of their DNA. But in nature, these recording events happen only rarely,” says senior author Luciano Marraffini, Ph.D., Head of the Laboratory of Bacteriology at Rockefeller. “We have identified a single mutation that causes bacterial cells to acquire genetic memories of viruses 100 times more frequently than they do naturally,” he adds. “This mutation provides a powerful tool for experiments in our lab and elsewhere, and could facilitate the creation of DNA-based data storage devices.” If a virus that a bacterium’s CRISPR system has recorded shows up again, an enzyme known as Cas9 (image) is dispatched to destroy it. The system’s precision has already made it an important tool for editing genomes, and scientists are looking toward other potential applications. For the current study, the team randomly introduced mutations into the gene for Cas9 and found that one of them prompts bacteria to acquire genetic memories more readily. Under normal conditions, if researchers expose 100,000 bacterial cells to the same potentially deadly virus, only one will typically acquire a DNA snippet that could enable it to survive a future attack.
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