Large conjugative plasmid mediates chromosomal Type VI secretion system cross transcriptional regulation and diverse bacterial pathogenicity [ChIP-Seq]

The type VI secretion system (T6SS) is a highly sophisticated nanomachine widely used by bacteria to achieve competitive advantage and to potentiate horizontal gene transfer. Plasmid conjugation plays crucial roles in bacterial evolution by driving adaptation to environmental stimuli and pathogenicity. The lethal effect mediated by T6SS is detrimental to horizontal gene transfer by conjugation, while bacteria have evolved T6SS repression mechanisms regulated by plasmid to accomplish conjugative transfer. Two TetR family regulators encoded by large conjugative plasmid (LCP) in Acinetobacter baumannii have been proved similar in T6SS restriction, which seems redundant in function. Here, the global regulation roles and multiple DNA binding sites of two plasmid-sourced TetRs were identified. The two TetRs showed distinct preferences in similar roles of T6SS inhibition and binding with DNA probes. Crystal structures of TetRs were solved for illuminating the regulatory mechanism and possible reasons for difference in functions. In addition, plasmid-sourced TetRs also significantly downregulated biofilm formation and bacterial colonization, as well as influenced bacterial virulence in cultured cells and murine pneumonia infection models. Taken together, this work comprehensively elucidates the roles and regulatory mechanisms of TetRs and clarifies their similarity and difference in function, providing insights into plasmid encoded chromosome regulation pathways. Overall design: Chromatin immunoprecipitation DNA sequecing (ChIP-Seq) for plasmid encoded TetR1 and TetR2 in A. baumannii ATCC 17978 cells.