Transcriptional regulation of mobilization and transfer of the Bacteroides conjugative transposon CTnDOT

Bacteroides;CTnDOT;conjugative transposon;conjugative transfer;mobilization;small RNA;transcriptional regulation

Waters, Jillian

关键词: Bacteroides;    CTnDOT;    conjugative transposon;    conjugative transfer;    mobilization;    small RNA;    transcriptional regulation;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/45596/Jillian_Waters.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Bacteroides spp. are a primary inhabitant of the human colon, and play an important role in the health of the human host as Bacteroides are important for nutrient acquisition, the breakdown of starches that would otherwise go undigested, and the management of relevant pathogens such as C. difficile.Although generally considered a commensal, Bacteroides can become an opportunistic pathogen if it should escape the colon.Bacteroides is the most commonly isolated causative agent of anaerobic infections, and these infections are rather difficult to treat due to the prevalence of antibiotic resistance within this genus.The prevalence of resistance determinants in Bacteroides is often due to mobile genetic elements.One such element is a conjugative transposon (sometimes referred to as an integrative conjugative element, or ICE) called CTnDOT, which is a 65 kb ICE that encodes resistance to the antibiotics erythromycin and tetracycline.A notable feature of CTnDOT is that excision from the donor chromosome and conjugative transfer are coordinately regulated upon exposure of donor cells to tetracycline (Tc).While no transfer is detected in the absence of Tc, upon Tc induction a regulatory cascade ultimately stimulates synthesis of the excision proteins, which are required for excision of CTnDOT from the chromosome.These proteins also have a regulatory role, in that they are required for the transcriptional activation of the 13 kb tra operon that encodes the mating apparatus. The work presented in this dissertation has characterized a negative regulator, RteR, that appears to prevent conjugative transfer of CTnDOT in the absence of Tc by possibly initiating the formation of an intrinsic terminator within traB, thus truncating the transcript so there is no substrate for translation, and hence no proteins are formed to assemble the mating apparatus.For the first time, we also describe the regulation of the CTnDOT mobilization region.These three genes that encode the relaxases and coupling protein required for mobilization are organized in an approximately 4 kb operon that is regulated upon Tc induction.The excision proteins Xis2d and Exc are required for enhancement of mob transcription upon exposure to Tc.This differs from the neighboring divergently transcribed tra operon, which does not require Exc, but also requires Xis2d and in addition Xis2c.A negative regulator is preventing mob transcription in the absence of Tc, and we currently predict that a gene encoded downstream of intDOT, orf2, is the mob transcriptional repressor.Taken together, the work described in this dissertation has further shed light on the intricate regulation governing the conjugative transfer of CTnDOT.