Identifying multidrug resistant efflux pumps in Rhizobium leguminosarum
Date
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Bacteria are vulnerable to a variety of toxins, especially those that can pass through their cell membrane. As a result, bacteria have evolved strategies to deal with these harmful substances, such as multidrug resistant (MDR) efflux pumps. Rhizobium leguminosarum is a Gram-negative, soil bacterium that fixes nitrogen through a symbiosis with legume hosts. Rhizobia are intrinsically resistant to many antibiotics and other toxins due to the impermeability of the outer membrane, but MDRs increase this resistance by extruding toxins that can cross the barrier. Rhizobia are closely related to a number of plant and animal pathogens, and therefore, understanding the mechanisms of toxin resistance in rhizobia could have significant implications to environmental, agricultural, and medical microbiology. For this study, I used a transposon mutagenesis approach to generate random mutations and screened 2000 mutants for decreased resistance to the toxins crystal violet, methyl viologen, acriflavine, cobalt, nickel, and cadmium. Of the 2000 mutants screened, four mutants were more sensitive to acriflavine, two were more sensitive to cobalt, one was more sensitive to cadmium and one was more sensitive to nickel, cobalt, and cadmium, when compared to the wild-type strain. MDR pumps are often low specificity transporters that can export a number of different toxins. Further analysis of the transposon mutants using MIC assays demonstrated that some mutants were also more sensitive to other toxins, such as the antibiotic erythromycin. One mutant was identified as containing as containing the transposon insertion in the gene RL0565, a putative solute-binding component of ABC transporter.