Bacteria as recorders thanks to the CRISPR-Cas genetic manipulation system

A comparison between magnetic tape and bacteria as tapes (Image courtesy Wang Lab/Columbia University Medical Center)
A comparison between magnetic tape and bacteria as tapes (Image courtesy Wang Lab/Columbia University Medical Center)

An article published in the journal “Science” describes the development of a system that uses the CRISPR-Cas genetic manipulation system to store information in living cells transforming them into a biological equivalent of a magnetic tape. A team of researchers from the Columbia University Medical Center modified a bacterium of the Escherichia coli family transforming it into a potential diagnostic or environmental monitoring tool thanks to its ability to record data.

The CRISPR (clustered regularly interspaced short palindromic repeats) acronym refers to prokaryotic DNA segments containing short repeated sequences. The expression CRISPR/Cas refers to a prokaryotic immune system conferring a genetic resistance to foreign elements. Subtypes of this enzyme-based system that evolved in different bacterial species are already being tested for medical purposes but this new research attempted to use them in another way.

The ability of CRISPR-Cas systems to write information in a cell’s DNA offers the possibility to use it as a memory compared by the researchers to a biological equivalent of a magnetic tape. Some experiments in this sense were already made in the past but this time the purpose wasn’t to record books but to look for a way to use cells to record biological activities.

This goal was achieved by modifying a plasmid, a fragment of DNA existing in cells but separated from that of the chromosomes that replicates on its own. After the modifications, the plasmid was able to create copies of itself in a cell responding to external signals. Another plasmid drives the recorder and marks time by expressing CRISPR-Cas system components.

If there are no external signals, only the plasmid that drives the recorder is active and adds copies of a space marker. In case of external signals, the other plasmid is also activated and this leads to the insertion of its marker. The result is a sequence that records the external signals over time.

In the experiment, the CRISPR-Cas-based system can handle at least three simultaneous signals and record them for days. An application example could see a patient ingest modified bacteria that record changes observed across the entire digestive tract.

This application of the CRISPR-Cas system is experimental, but in the future it will allow to exploit various markers that can be altered depending on status changes in the human body. This will allow its use for diagnostic purposes to reach body parts otherwise difficult if not impossible to examine.

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