UBC Theses and Dissertations
Environmental conditions regulating gene transfer in Rhodobacter capsulatus Bernelot Moens, Rachel
Rhodobacter capsulatus is a metabolically versatile α-proteobacterium that produces a bacteriophage-like particle called the gene transfer agent (RcGTA) that is capable of mediating horizontal gene transfer. RcGTA particles transfer random 4.5 kb fragments of genomic DNA that integrate into recipient genomes by allelic replacement. This thesis addresses certain environmental conditions, in particular carbon limitation and the presence of subinhibitory concentrations of antibiotics, that influence gene transfer by RcGTA. A new transduction assay was developed to test the effects of various substances on gene transfer. Using this transduction assay, both carbon limitation and low levels of DNA gyrase inhibitors were found to increase the frequency of gene transfer, although by different mechanisms. Carbon limitation caused an increase in production and release of RcGTA. This effect was a general response to carbon limitation, and was independent of carbon source. Gyrase inhibitors, on the other hand, did not influence production or release of RcGTA and instead were thought to act on the recipient cells via DNA gyrase. GyrB overexpression constructs were made in order to confer resistance to novobiocin. The presence of these constructs negated the novobiocin-mediated increase in gene transfer. The results of this thesis suggest that certain antibiotics as well as carbon limitation affect gene transfer in R. capsulatus and may be relevant to microbial genetic exchange in natural ecosystems.
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