Efflux pumps are proteins located in the cell membrane that actively transport a wide variety of substrates. They are well known for their role in antimicrobial resistance and contribution to the multidrug resistance phenotypes observed among clinical strains of human pathogens. However, their primary function and/or those of their environmental precursors in the pre-antibiotic era and the advantage they may confer to bacterial species for colonization of a habitat (i.e. soil, rhizosphere, marine environment) remain underexplored. To fill this gap our research focus on the role of the resistance-nodulation-cell division (RND) pumps, which are highly prevalent and diverse in Gram-negative bacteria, using phylogenetic approaches combined to metagenome analysis and bacterial genetic.