Humans have harnessed the CRISPR (clustered regularly interspaced short palindromic repeats) system that bacteria use to remove foreign DNA from their genomes that has been inserted by viruses. Scientists are now using CRISPR remove faulty genes and correct genetic mutations, but we are not the first species to re-purpose CRISPR for our own benefit. According to a recent study by researchers at the University of Copenhagen, there are primitive bacterial parasites that have weaponized the system to achieve their own aims and they are believed to have been doing so for millions of years.
The researchers chose Type IV CRISPR-Cas for their study, which is one of the least known of the six CRISPR-Cas systems found in nature. The Type IV CRISPR-Cas system is not found in the genome of bacteria, but in plasmids, which are small DNA molecules located within bacteria that are separate entities to the chromosomal DNA.
The researchers found the Type IV CRISPR-Cas system is present in a diverse range of taxa and identified several previously unknown subtypes of the Type IV CRISPR-Cas system, which may have a purpose other than a defensive role to protect against parasites and viruses. The researchers also found evidence of cross-talk between different types of CRISPR system within the same host.
One of the key findings of the research is the Type IV CRISPR-Cas system is exploited by a diverse range of invading mobile genetic elements (MGEs) and that plasmids use the Type IV CRISPR-Cas system to compete with other plasmids within the same bacterial host. “We humans have only recently begun to exploit nature’s CRISPR-Cas systems, but as it turns out, we are not the first. These ‘primitive parasites’ have been using them for millions of years, long before humans. It is quite a humbling realization,” said lead researcher of the study, Rafael Pinilla-Redondo.
The research could prove to be important for use in medicine to tackle one of the most serious threats to human life: Multi-drug resistance in bacteria. Many bacterial strains have evolved resistance to almost all drugs currently in use. Bacterial resistance to drugs is often due to bacteria having antibiotic resistance genes in their plasmids, which are passed on to other bacteria when they replicate.
Since the Type IV CRISPR-Cas system is harnessed by plasmids to compete with other plasmids, it is possible that the system could be used to target plasmids with antibiotic resistant genes. As with other CRISPR systems, Type IV CRISPR-Cas could be programmed by researchers to eliminate resistance to certain drugs as an alternative to the costly and difficult process of finding and developing new antibiotics.
You can read more about the study in the paper – Type IV CRISPR–Cas systems are highly diverse and involved in competition between plasmids – which was recently published in the journal Nucleic Acids Research. DOI: 10.1093/nar/gkz1197