The role of Bacteroides conjugative transposons in the spread of antibiotic resistance genes, and, The role of recA in DNA damage repair in Deincoccus radiodurans.

摘要

The work presented in this thesis covers two unrelated projects. The first project involves using Bacteroides species, which are normal residents of the human colon, as a model for investigating the horizontal transmission of antibiotic resistance genes in the environment. The data presented in this thesis shows that an open genetic conduit exists between gram positive bacteria that reside in the intestinal lining of cows and gram negative bacteria that reside in the human colon. We have identified a 7-kilobase segment of DNA, located on a Bacteroides conjugative transposon (CTnBST), that carries a gene for erythromycin resistance (ermB). The same DNA sequence (100% identical) had been previously identified in the genome of Arcanobacterium pyogenes, a gram positive opportunistic pathogen that is a normal resident of the intestinal tract of cows. In addition, in order to better understand the molecular mechanisms behind the transmission of antibiotic resistance genes the development of an assay for studying the sequence requirements for integration of another Bacteroides conjugative transposon, CTnDOT, is presented. The second project involves identifying novel mechanisms of DNA damage resistance and DNA damage repair in the extremely radiation resistant organism Deinococcus radiodurans. Previously published studies had suggested that the RecA protein, which is required for repair of DNA damage, from D. radiodurans is unique among RecA proteins and that this uniqueness accounts for this organism's ability to repair massive amounts of damage to its genome. The work presented in this thesis shows that RecA from D. radiodurans may not be as unique as previously though. Contradicting a previous study we show that RecA from E. coli can partially compliment a RecA null mutant in D. radiodurans. In addition evidence is presented that suggests that RecA from D. radiodurans interacts with another protein CinA (transcribed from the same operon as D. radiodurans recA) and that this interaction may play a role in chromosome integrity and cell viability.