CRISPR, herd immunity and transduction - an unexpected way of how bacteria have sex

Unlike most eukaryotes, bacteria reproduce by binary fission, which is devoid of recombination. Recombination is known to be able to speed up adaptation by bringing beneficial alleles arising in different individuals together. In a purely clonal bacterial population, however, the beneficial alleles compete with each other in a process called clonal interference, which slows down adaptation. Although bacteria lack recombination as it occurs in eukaryotes, they can occasionally exchange genetic information directly between individuals in a process called horizontal gene transfer (HGT). How much HGT affects evolutionary dynamics within bacterial populations, however, remains largely unclear. In my presentation I will show that in bacterial populations a combination of CRISPR-based herd immunity and HGT mediated by general transducing phage can result in coexistence of CRISPR+ and CRISPR– strains and the phage in the population. As a result, it allows for a continuous gene flow from the susceptible fraction of the population to the resistant one. This gene flow then leads to adaptation by recombination, which exceeds adaptation by de novo mutations by one to two orders of magnitude, and to some extent can circumvent clonal interference. Therefore, the combination of CRISPR, herd immunity and transduction can essentially be interpreted as an unexpected way of how bacteria have sex.

The seminar will be hosted using Zoom. A Google calendar invite featuring the Zoom link will be sent to Biology staff and students before the seminar date. For all enquiries please contact Biology DMT Hub.