Ten potential CRISPR competitors
10 new protection systems have been found in bacteria
Marina Astvatsaturyan, Echo of Moscow
Long before becoming a popular tool for gene editing, the CRISPR system served bacteria as a natural defense against viral interventionists, which in bacteria are called phages.
As established by researchers from the Weizmann Institute of Science in Israel, the authors of an article in Science (Doron et al., Systematic discovery of antiphage defense systems in the microbial pangenome), this is not the only mechanism of bacterial protection: there are at least 10 more sets of bacterial genes with a similar protective function.
Phages that kill bacteria use the genetic apparatus of bacteria for their reproduction – the production of viral DNA. But some bacteria manage to protect themselves from a phage attack using the CRISPR system, which preserves pieces of the DNA of the invader attacking it so that the bacterium can recognize and repel such a threat in the future. At the same time, as the head of the new study Rotem Sorek notes in the Bacterial Immune Systems Take the Stage press release, only 40 percent of bacteria are endowed with the CRISPR system. And this prompted Sorek and his colleagues to look for other defense mechanisms.
Based on the fact that genes associated with the protective functions of the cell, as a rule, form clusters in the genome, Israeli researchers carefully analyzed the genetic information about 45 thousand microbes, and their hopes were justified. They identified groups of genes with unknown functions that were localized near known genes related to protection from external intrusions.
Many bacteria, in which such gene families were found, turned out to be inhabitants of special ecological niches, for example, the ocean floor.
The scientists used the revealed genomic information to synthesize the corresponding DNA fragments, which were then inserted into the common bacteria Escherichia coli and Bacillus subtilis. Bacterial cultures were infected with phages and observed how they resist these invasions with the exclusion of certain introduced genes. If the removal of some genes affected the ability of bacteria to repel phage attacks, it could be concluded that these genes belong to the defense system.
Nine new groups of bacterial genes turned out to be antiphage, and one system protected against plasmids – this is also a kind of foreign DNA. The new systems were named Zorya, according to Sorek, cited by Science News (Scientists find 10 new defense systems used by bacteria), "in honor of the deity of Slavic mythology, which has protective properties."
According to the authors, the data obtained indicate the possibility of a common origin of the immune systems of bacteria and more complex organisms, because some of the identified genes contain DNA fragments known as an important part of the immune system of plants, mammals and invertebrates.
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