Bacteria, as unicellular organisms, colonize all terrestrial environments, playing critical roles in both human health and ecological systems due to their genetic and metabolic diversity. Horizontal gene transfer (HGT) through direct contact between bacteria enables them to acquire new functions, such as antibiotic resistance or pollutant degradation, by exchanging DNA with each other. This research focuses on an integrative and conjugative element (ICE) known as ICEclc, which enables bacteria to degrade specific compounds, like 3-chlorocatechol (3-CBA). ICEclc serves as a prime model for studying DNA transfer due to its high transfer frequency. However, only a subset of the bacterial population becomes competent for ICEclc transfer, raising questions about the cellular and environmental regulations governing this transfer.
This research first explores how ICEclc replication in competent cells influences transfer efficiency. Fluorescent markers tracked the ICEclc replication, revealing that competent cells with higher ICEclc copy numbers have a greater probability of successful transfer.
Next, the physiological and environmental signals, such as micropollutants, that induce oxidative stress conditions favoring horizontal gene transfer were analyzed. Gene expression analyses shows that growth on 3-CBA impacts the activity of numerous genes, although no specific group being particularly distinct.
The role of 3-CBA metabolism in ICEclc transfer was also analyzed, revealing that the only presence of this compound is insufficient to activate ICEclc. However, disruptions in the 3-CBA metabolism significantly reduces the transfer rates, demonstrating the importance of this metabolism pathway in the process.
Finally, the Transfer Competence Regulon (TCR) was identified as a crucial set of genes involved in the ICEclc transfer process. Deletion of specific genes within this regulon confirmed their essential role in successful DNA transfer.
This thesis advances the understanding of ICEclc transfer mechanisms, uncovering complex regulatory pathways that may apply to other ICEs, offering insights into bacterial evolutionary mechanisms.