Shedding light on antibiotic resistance

In the fight against antibiotic resistance, it is essential to study the mechanisms of gene transfer between bacteria. Antibiotic resistance can spread from one bacterium to another, whether they belong to the same species or not, via different pathways such as conjugation, which is a transfer of genetic material through direct contact between two bacteria. Pascale B. Beauregard, a professor in the Department of Biology at the Université de Sherbrooke, set out to understand the transfer of a DNA strand from a donor bacterium to a recipient bacterium in Bacillus subtilis.

Harmless to humans, this bacterium is frequently used as a genetic model in research. But it also produces a biofilm, which is a community of several bacteria encased in polymers they secrete. These polymers form a kind of jelly, rather like the one that floats on the surface of kombucha. However, the conjugation mechanism had never been studied in biofilm bacteria, even though this is the form in which most of them are found in the environment.

First, the research team mixed bacteria with and without a particular DNA strand, to investigate the frequency with which the strand would be transferred under different conditions (with and without biofilm). They found that gene transfer was 100 to 10,000 times more frequent in a biofilm environment. The stability of the biofilm structure enabled bacteria to remain in contact for longer, thus favouring DNA transfer between them.

The team also examined conjugation in the biofilm and found it to be highly heterogeneous. In some areas, large numbers of bacteria were observed to have acquired the new genes, but in others, very few. The transfer rate from donor bacteria was similar throughout the biofilm, but in some cases, bacteria that received a new gene were hyperactivated and became "super-infectors" themselves.

Although the results cannot be generalized at present, this research contributes to our understanding of antibiotic resistance mechanisms.

References

Lécuyer, F., Bourassa, J.-S., Gélinas, M., Charron-Lamoureux, V., Burrus, V. et Beauregard, P. B. (2018). « Biofilm formation drives transfer of the conjugative element ICEBs1 in Bacillus subtilis », mSphere, 3(5). doi : 10.1128/e00473-18.

Bourassa, J.-S., Jeannotte, G., Lebel-Beaucage, S. et Beauregard, P. B. (2022). « Second-generation transfer mediates efficient propagation of ICEBs1 in biofilms ». Journal of Bacteriology, 204(10). (Editor’s Pick, Commentary and Cover)