D. Bacterial sensing of antimicrobial stress
Bacterial sensing of bacitracin-induced stress in Enterococci - characterization of a novel regulatory protein BcrR
Funded by Marsden Fund, Royal Society of New Zealand and Otago Medical School Research Foundation
Dr Susanne Gebhard
Overview of Research
Bacteria respond to antibiotic selection pressure by developing and acquiring resistance mechanisms that enable them to survive and multiply. Some of these resistance mechanisms involve membrane-bound proteins that sense the presence of antibiotics in the environment and relay this signal to the inside of the cell to evoke an appropriate response. For this purpose, bacteria typically use signal transduction (phosphorelay) systems that consist of two components: a membrane-localized sensor kinase and a DNA-binding response regulator.
Recent work from our laboratory has identified a deviation from this paradigm for the antibiotic bacitracin. We have identified a novel regulatory protein BcrR that singularly controls the expression (on/off) of the bcrAB genes in response to bacitracin. Our data represents the first description of genes that are essential for bacitracin resistance in the genus Enterococcus. BcrR is unique because the protein elicits both the sensing and activation of gene expression (ie. it is not a two-component system). The protein itself consists of two domains: a C-terminal domain of four membrane-spanning helices and an N-terminal DNA-binding domain (see figure), suggesting that BcrR acts as a sensor and transducer of bacitracin availability. The process by which BcrR senses and activates transcription of the bcrAB genes is unknown.
The aims of this study are to use the BcrR protein as a model to study sensing of antibiotics by bacteria. Because BcrR is not a two-component system, the BcrR protein represents a prototype for understanding how a single protein can sense an antibiotic and activate gene expression accordingly.
(See downloads section below for PDFs)
D1 Gebhard, S., Gaballa, A., Helmann, J.D. and Cook, G.M. Direct stimulus perception and transcription activation by a membrane-bound DNA binding protein. Molecular Microbiology 73:482-491 (2009)
D2 Gauntlett, J.C., Gebhard, S., Keis, S., Manson, J.M., Pos, K.M. and Cook, G.M. Molecular analysis of BcrR: a membrane-bound bacitracin sensor and DNA-binding protein from Enterococcus faecalis. Journal of Biological Chemistry 283:8591-8600 (2008)
D3 Manson, J.M., Keis, S., Smith, J.M.B. and Cook, G.M. Acquired bacitracin resistance in Enterococcus faecalis is mediated by an ABC transporter and a novel regulatory protein BcrR. Antimicrobial Agents and Chemotherapy 48: 3743-3748 (2004)
D4 Manson, J.M., Smith, J.M.B. and Cook, G.M. Persistence of vancomycin-resistant Enterococci in New Zealand broilers after the discontinuation of avoparcin use. Applied and Environmental Microbiology 70: 5764 - 5768 (2004)
D5 Manson, J.M., Keis, S., Smith, J.M.B. and Cook, G.M. Characterization of a vancomycin-resistant Enterococcus faecalis (VREF) isolate from a dog with mastitis: Further evidence of a clonal lineage of VREF in New Zealand. Journal of Clinical Microbiology 41:3331-3333 (2003)
D6 Manson, J. M., Keis, S., Smith, J.M.B. and Cook, G.M. A clonal lineage of VanA-type Enterococcus faecalis predominates in vancomycin-resistant enterococci isolated in New Zealand. Antimicrobial Agents and Chemotherapy 47:204-10 (2003)
D7 Tannock G.W. and Cook, G.M. Enterococci as members of the intestinal microflora of humans. In The Enterococci: Pathogenesis, molecular biology and antibiotic resistance. ASM Press (2002) 101-132.