Abstract:
Horizontal gene transfer plays a crucial role in bacterial evolution, allowing for the rapid acquisition of new genes that enhance survival, adaptability, and competitiveness. Among mobile genetic elements, integrative and conjugative elements (ICEs) are particularly significant as they integrate into the host chromosome, ensuring stable inheritance, while retaining the ability to excise and transfer via conjugation. Proper regulation of ICE gene expression is essential to balance stability within the host genome with activation for transfer. My work uncovered a critical role for transcription termination and antitermination in ICE regulation. Working with the well-characterized ICE Tn916 that is found in several species of Gram-positive bacteria, I identified a strong intrinsic terminator (T1) at the left end of the element that insulates ICE gene expression from host promoters, preventing premature expression of DNA processing genes that could lead to host fitness defects. I further discovered an antitermination system, canT (conjugation-associated antitermination), that overrides T1-mediated termination post-excision, ensuring proper gene expression that is required for conjugative DNA transfer. Working with ICEBs1 from Bacillus subtilis, I identified multiple functional intrinsic terminators within genes that are essential for conjugation, including TerconQ, the strongest terminator in the conjugation operon. Additionally, I found a small DNA region between the major operon promoter and the terminator TerconQ that is required for conjugation and is likely to be needed for antitermination. Together, my findings reveal that transcription termination and antitermination play an intricate role in the regulation of two very different ICEs. This regulation can influence ICE stability, host fitness, and the efficiency of horizontal gene transfer. This study expands our understanding of how ICEs are regulated at the transcriptional level, shedding light on broader principles of bacterial genome plasticity and evolution.
Advisor: Alan Grossman (Biology)
TDC Members: Steve Bell (chair), Gene-Wei Li, Ann Hochschild (external)