A Conserved but Atypical ABC Transporter in the Alpha-proteobacterium Sinorhizobium meliloti Confers Resistance to a Range of Antimicrobials
Klara Christensen
Department of Biology
Faculty Supervisor: Joseph C. Chen
Sinorhizobium meliloti is a Gram-negative bacterium known for its ability to form endosymbiosis with compatible legume plants. A deletion of an ABC transporter, encoded by the gene SMb21269, confers an increased sensitivity to a range of antimicrobials. This gene encodes both the nucleotide binding (NBD) and transmembrane domain (TMD) associated with an ABC transporter, as well as a third unknown domain. Removing this unknown domain improves the antimicrobial resistance past wild-type SMb21269. Three different point mutations were introduced into specific conserved residues of the NBD necessary for function in other ABC transporters. These mutants only received a partial loss of antimicrobial resistance. Three other genes have been identified to likely be involved with SMb21269: SMb21265 and SMb21252, which both encode a glycosyltransferase, and SMb21256, which encodes a nucleotide sugar oxidase. Deletions of these genes result in increased sensitivity to antimicrobials matching that of SMb21269. It is currently not understood what is the mechanism by which these genes confer resistance to antimicrobials. Investigation of this mechanism can further our understanding of antibiotic resistance in alphaproteobacteria, as well as how soil microbes compete.