Genome-wide analysis of multidrug efflux in the plant-pathogenic bacterium Pseudomonas syringae

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Multidrug efflux (MDE) transporters are major contributors to bacterial resistance towards antibiotics. In contrast to the well-understood role of MDE in clinically relevant microbes, only little is known about MDE transporters in environmental bacteria. This project aims to identify and characterize all MDE pumps in the plant pathogen Pseudomonas syringae and to gain in-depth knowledge about their regulation and natural functions. MDE pumps may play an important role in the adaptation of P. syringae to its respective host plants by protecting them against plant antimicrobials. P. syringae is sub-divided into pathogenic variants (pathovars) which vary according to their host range. Available genome sequences of three different P. syringae pathovars will be used to develop a microarray containing genes of all members of transport protein families that include MDE systems. The microarrays will be used to identify transporters that are expressed after treatment with antibiotics, antimicrobial plant metabolites, and in planta. The to-be-tested P. syringae strains infect plants belonging to different plant families, each producing a different spectrum of antimicrobial metabolites. Thus, the diversity of plantborne metabolites will be screened as substrates of MDE transporters potentially shedding light on the contribution of MDE systems on host specificity. Putative MDE proteins will be cloned to determine substrate specificity, to search for natural substrates, and to study their transcriptional regulation. Because not all MDE transporters might show an increased expression in response to antibiotics, we will furthermore clone and DFG Research proposal - Matthias Ullrich - Multidrug efflux in plant pathogens 3 characterize genes that show sequence similarities to known MDE pumps from other organisms. Mutagenesis will be used to reveal the role of these transporters during pathogenesis.