PhD defense - Meng Wen (eq. Yamaichi - Genome Biology dpt)

Title: “DNA transactions during the establishment of conjugative plasmid transfer”

Abstract: 
The worldwide spread of antimicrobial resistance (AMR) has emerged as one of the most serious public health challenges. Bacteria can develop AMR by spontaneous mutations or acquiring resistance genes through horizontal gene transfer such as transduction, transformation, and conjugation. Among them, conjugation is widely considered to be the most effective pathway for the transmission of AMR genes by conjugative plasmid. Indeed, successful conjugative transfer of plasmid which includes establishment in new host cell, requires complex DNA transaction, such as plasmid DNA circularization, double-strand DNA synthesis and prompt gene expression. However, detailed molecular mechanisms of this dynamic process remain elusive.

In my thesis, I developed a new method, ED-TA, for achieving Elimination of Donor cells for Transconjugant Analysis. ED-TA method enables genome-wide analysis of DNA reactions in recipient cells during conjugation. Based on ED-TA, I carried out RNAseq which unveiled the transcriptome profiling of pESBL at early stages of conjugation. Additional genetic experiments collectively showed that the ssDNA promoter in the leading region (the first fragment enters the recipient cells which encoded anti-defense systems) induces the expression of certain plasmid genes in the early stages of conjugation, and these genes play an important role in plasmid establishment in the recipient cell. These innovations and insights will be helpful for future understanding of molecular mechanisms and subsequent development of targeted strategies to block the transmission of drug-resistant plasmids. In addition, the SOS response is believed to be a bacterial defense system against foreign DNA (such as conjugative plasmids). However, with emerging controversial results, I further investigated the biological significance of the SOS response and the regulation of SOS inhibitor during conjugation.

Members of the jury:
Dr. Sarah BIGOT (DR CNRS, MMSB Lyon) Rapportrice & Examinatrice
Dr. Bianca SCLAVI (DR CNRS, IBPS Paris) Rapportrice & Examinatrice
Dr. Olga SOUTOURINA (PR Univ Paris-Saclay, I2BC) Examinatrice
Dr. Laurent AUSSEL (PR Aix-Marseille Univ. LCB Marseille) Examinateur