A collaborative team from the Department of Microbiology and Immunology and a university in the Netherlands is a step closer to unlocking the secrets of bacterial immune systems.
Just like humans, bacteria are constantly under attack by viruses that try to infect them by injecting viral DNA. CRISPR-Cas systems can remember and destroy invading DNA by storing short, invader-derived, pieces of DNA (called 'spacers') into their genetic memory banks.
A previous study demonstrated that that viruses and plasmids, which can avoid recognition by mutating their DNA, will trigger the bacteria's CRISPR-Cas system to respond by quickly acquiring new immunological memories from these mutated threats. This process is called 'primed adaptation'.
In the team's latest study, published this week in the prestigious journal Nature Communications, Associate Professor Peter Fineran's team sought to understand how these new memories were selected during the primed adaptation response.
"We infected the bacteria with plasmids not previously encountered, or with mutated plasmids triggering the primed adaptation response. By making use of the advances in next generation sequencing through New Zealand Genomics Ltd, we analysed more than 20 million newly acquired spacers."
The team discovered that the acquisition of memories from plasmids not previously encountered was very inefficient in comparison to the mutated plasmids. By studying the order in which these new memories were acquired, the researchers developed a new model for primed adaptation. The data indicated that acquisition of new immunological memory occurs not only during primed adaptation but also as a consequence of direct defence against invading genetic elements that have not mutated to evade recognition by the CRISPR-Cas system.