Bacteroides fragilis is the most significant anaerobic pathogen in humans, which is attributable to a number of virulence factors and to its ability to acquire antibiotic resistance by DNA transfer. Although transfer of antibiotic resistance has been demonstrated in vitro, the mechanisms of DNA transfer are unknown. To date, three types of transfer factors have been identified. They include conjugal plasmids, mobilizable transposons, and tetracycline transfer elements. These factors function independently but also interact with one another to facilitate and enhance transfer.
The goal of my laboratory's research has been to determine the mechanisms of transfer of plasmids pBFTM10 and pLV22a and the mobilizable transposon Tn5520 as models for understanding DNA transfer in B. fragilis. We use transposon mutagenesis, subcloning, DNA sequencing, gel retardation assays, DNA footprinting, and complementation studies to determine which proteins are required for plasmid transfer. Thus far, depending on the transfer factor, we have determined that one, two, or three proteins plus a nick site are required for transfer, and we are currently determining protein functions. We are also determining which specific protein-DNA interactions are required for transfer initiation.
Remaining questions include: (1) What are the functions of the transfer proteins? (2) What does the host provide in the mating process, and how is this controlled? (3) What controls DNA transfer? Answers to these questions will allow us to then ask what the molecular relationships are between plasmid transfer and other transfer factors, such as the tetracycline transfer element.
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Vedantam G, Knopf S, Hecht DW. (2006).
Bacteroides fragilis mobilizable transposon Tn5520 requires a 71 base pair origin of transfer sequence and a single mobilization protein for relaxosome formation during conjugation.
Molecular Microbiology 59:288-300.
Last Reviewed: June 1, 2010