1. Gene arrangement in the B
Gene arrangement in the B. fragilis bme5 efflux pump operon and analysis of the B. fragilis bme5 gene sequences.
Gene arrangement in the B. fragilis bme5 efflux pump operon and analysis of the B. fragilis bme5 gene sequences. The bme operon codes for the three components of the RND efflux pumps: bmeA codes for the linker protein which connects the pump to the outer membrane barrel, bmeB codes for the efflux pump, and bmeC codes for the outer membrane barrel through which the substance is exported. Most of the B. fragilis bme pump operons are in the order (bmeA-bmeB-bmeC) but some (e.g., bmeABC5, shown here) are different. Another distinctive feature of bmeABC5 is that it has two promoter regions (indicated by the gold stars). Genomic analysis revealed a putative regulator sequence upstream of bmeABC5 (bmeR5). We demonstrated that the BmeR5 protein binds to the first intergenic region (IT1) but not to the second or third intergenic region (IT2 or IT3). A closer analysis of IT1 revealed that it had two inverted repeats (IR) (GGGAAT******ATTCCC) separated by six nucleotides. We analyzed a clinical metronidazole-resistant isolate of B. fragilis and found a G→ T mutation in the IT1 region. Gel shift assays demonstrated that BmeR5 was no longer able to bind to this region.
Hannah M. Wexler Clin. Microbiol. Rev. 2007; doi: /CMR