Characterization of AcrD, a resistance-nodulation-cell division-type multidrug efflux pump from the fire blight pathogen Erwinia amylovora.
BACKGROUND
Multidrug efflux pumps are membrane translocases that have the ability to extrude a variety of structurally unrelated compounds from the cell. AcrD, a resistance-nodulation-cell division (RND) transporter, was shown to be involved in efflux of highly hydrophilic aminoglycosides and a limited number of amphiphilic compounds in E. coli. Here, a homologue of AcrD in the plant pathogen and causal agent of fire blight disease Erwinia amylovora was identified.


RESULTS
The substrate specificity of AcrD was studied by overexpression of the corresponding gene from a high-copy plasmid in E. amylovora Ea1189-3, which is hypersensitive to many drugs due to a deficiency of the major multidrug pump AcrB. AcrD mediated resistance to several amphiphilic compounds including clotrimazole and luteolin, two compounds hitherto not described as substrates of AcrD in enterobacteria. However, AcrD was not able to expel aminoglycosides. An acrD mutant exhibited full virulence on apple rootstock and immature pear fruits. RT-PCR analysis revealed an induction of acrD expression in infected apple tissue but not on pear fruits. Moreover, a direct binding of BaeR, the response regulator of the two-component regulatory system BaeSR, to the acrD promoter was observed as has already been shown in other enterobacteria.


CONCLUSIONS
AcrD from E. amylovora is involved in resistance to a limited number of amphiphilic compounds, but in contrast to AcrD of E. coli, it is not involved in resistance to aminoglycosides. The expression of acrD was up-regulated by addition of the substrates deoxycholate, naringenin, tetracycline and zinc. AcrD appears to be regulated by the BaeSR two-component system, an envelope stress signal transduction pathway.
Daniel
D
Pletzer
School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany. h.weingart@jacobs-university.de.
Helge
H
Weingart
D026905:Amino Acid Transport Systems / Q000235:genetics* / Q000378:metabolism*; D000617:Aminoglycosides / Q000378:metabolism; D000900:Anti-Bacterial Agents / Q000378:metabolism; D017920:Antiporters / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D024881:Drug Resistance, Bacterial; D044084:Erwinia amylovora / Q000201:enzymology* / Q000235:genetics*; D017353:Gene Deletion; D015870:Gene Expression; D020869:Gene Expression Profiling; D027845:Malus / Q000382:microbiology; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism; D018517:Plant Roots / Q000382:microbiology; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D031989:Pyrus / Q000382:microbiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013379:Substrate Specificity; D013501:Surface-Active Agents / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism; D014774:Virulence
D026905:Amino Acid Transport Systems; D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D017920:Antiporters; D001426:Bacterial Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D013501:Surface-Active Agents; D015534:Trans-Activators; C063930:ArcD protein, Bacteria