SELECTIVE FORCES IN THE RHIZOSPHERE GENERATE A FUNCTIONAL DIVERSIFICATION OF ANTIBIOTIC RESISTANCE GENES

Background: Soil is an important reservoir of antimicrobial producing species, which correlates with a high abundance of resistance mechanisms against these antimicrobial molecules. The ongoing increase in antibiotic resistance genes (ARG) in anthropogenic environments calls for a better understanding of the source, the abundance and the spread of these ARG.

Objective: Exploring the differentiated functions of resistance determinants and specifically β-lactamase genes in their original environment.

Methodology: In a molecular and physiological approach, we are studying β-lactam resistance genes present in undisturbed rhizosphere soils and their benefits and burdens. So far, we demonstrated that subtoxic concentrations of cell wall-targeting antibiotics induced β-lactamase expression [Bucher et al., 2015, Bucher et al., 2016], suggesting an underlying function of these enzymes. Furthermore, we confirmed the presence of β-lactam resistant Bacilli communities carrying β-lactamases with distinct activity spectra. We now aim to determine the role of these differential activities in stabilizing resistant Bacillus species in the rhizosphere microbiomes.

Conclusion: Studying the physiological role of these β-lactamases will elucidate the evolutionary purpose and diversification of these ARG, and reveal possible novel functions. Additionally, knowledge about the natural selective pressures in the rhizosphere that activate ARG expression is crucial to understand how to limit the spread of these genes.