Bacterial immune system has a better memory than expected

April 18, 2014
Bacterial immune system has a better memory than expected
A sample with phages growing on a bacterium is pipetted onto agar. The clear spots, called plaques, arise if a single phage particle multiplies and kills all the surrounding bacteria. At number 3, more than 100 plaques can be seen, which indicates that the same number of phages capable of infecting this type of bacterium is present in the sample.

Bacteria's memories of hostile viruses are stronger than thought. Even when the intruders change their DNA sequence, the immune system of bacteria can recognise these and subsequently destroy them. That is the conclusion of NWO Vidi researcher Stan Brouns in the journal PNAS.

Bacteria are continuously attacked and killed by intruding viruses. To survive this conflict have developed an immune system, called CRISPR-Cas (clustered regularly interspaced short palindromic repeats–CRISPR associated). Although there are other less-developed immune mechanisms, CRISPR-Cas has a 'memory', as a result of which the bacteria are protected against viral infections.

Prior knowledge

Bacteria add pieces of DNA from intruding phages (small viruses that only infect bacteria) or plasmids (DNA that exchanges information between unicellular organisms) to the memory system of CRISPR-Cas. The DNA of the phages is subsequently broken down and the intruder is rendered harmless. However, phages avoid being recognised by the CRISPR-Cas system by changing their DNA sequence. This makes it harder for the immune system of the bacteria to identify the viral DNA.

Microbiologist Dr Stan Brouns from Wageningen University has discovered that the immune system of bacteria is more robust than had previously been thought: it can recognise viruses by making use of vague memories. Somehow or other the takes up pieces of the now altered DNA and destroys the intruder. In a certain sense the bacterium repeats the same trick but now with prior knowledge. As a vague memory has already been stored in the memory the process now proceeds faster and more efficiently. The CRISPR-Cas system therefore seems able not only to resist recent intruders but also old intruding viruses and intruders related to new viruses.


The CRISPR-Cas system appears to have a better memory against intruders than had previously been thought; it makes bacteria resistant to external pathogens and therefore gives bacteria an advantage in the evolutionary struggle with intruding . This knowledge can be used to accelerate the resistance of bacteria to phages that threaten milk fermentations (like in yoghurt and cheese).

This research is part of the Vidi project of Stan Brouns. Vidi is an individual grant awarded to talented and creative researchers. The funding instrument makes it possible for researchers to do research of their own choice.

Explore further: New light shed on key bacterial immune system

More information: Peter C. Fineran, Matthias J. H. Gerritzen, María Suárez-Diez, Tim Künne, Jos Boekhorst, Sacha A. F. T. van Hijum, Raymond H. J. Staals, and Stan J. J. Brouns. "Degenerate target sites mediate rapid primed CRISPR adaptation." PNAS 2014 ; published ahead of print April 7, 2014, DOI: 10.1073/pnas.1400071111

Related Stories

New light shed on key bacterial immune system

April 7, 2014

New insights into a surprisingly flexible immune system present in bacteria for combating viruses and other foreign DNA invaders have been revealed by researchers from New Zealand's University of Otago and the Netherlands.

Researchers clarify bacterial resistance

June 24, 2011

Just like plants and animals, bacteria have a range of defence mechanisms against viruses and other threats. Dutch researchers at the Wageningen Laboratory for Microbiology and their American and Russian colleagues have largely ...

The many faces of the bacterial defense system

April 30, 2013

Even bacteria have a kind of "immune system" they use to defend themselves against unwanted intruders – in their case, viruses. Scientists at the Helmholtz Center for Infection Research (HZI) in Braunschweig, Germany, were ...

Recommended for you

Biologists show how plants turn off genes they don't need

August 22, 2017

A plant has one genome, a specific sequence of millions of basepairs of nucleotides. Yet how this genome is expressed can vary from cell to cell, and it can change as a plant goes through various life stages, from germination ...

Evolutionary arms 'chase'

August 21, 2017

In nature, plants engage in a never-ending battle to avoid being eaten. Unable to run away, plant species have evolved defenses to deter herbivores; they have spines, produce nasty chemicals, or grow tough leaves that are ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.