Anthropogenic influences on bacterial horizontal gene transfer

In recent years, the use of antibiotics has grown and consequently the amount that is being thrown and contaminate the environment also grew. This led us to study whether the presence of antibiotics in the environment could affect and increase conjugation in bacteria. Conjugation, a horizontal gene transfer mechanism (HGT), is known to be an important factor in the transfer of resistance genes between bacteria and therefore impair our ability to fight bacteria with antibiotics.

Using fluorescence, we tested conjugation efficiency in different environmental relevant concentrations of gentamicin antibiotics. We used reporter strains of the bacterium Phaeobacter inhibens into which plasmids expressing genetic modules related to conjugation were introduced. In addition, we measured the bacteria’s growth rate to see if the physiological state of the bacteria affects the process.

We found similar trends of gene transfer increase in an antibiotic-free and high concentrations of antibiotic environments, yet the most significant increase was found in the high antibiotic concentrations. In contrast, intermediate gentamicin concentrations did not show a clear trend in the gene transfer. In addition, we observed that the treatment with the highest antibiotic concentration had the greatest conjugation efficiency.

These results show that although there is no clear trend in all treatments, high presence of antibiotics could increase the amount of conjugation, which might cause antibiotic-resistance to spread rapidly among bacteria, thus impairing its therapeutic effect.