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