Role of the SOS response in the conjugative transfer and genome maintenance of multidrug resistance Salmonella Genomic Island 1

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English. Salmonella Genomic Island 1 (SGI1) is a multidrug resistance integrative mobilizable element specifically mobilized in trans by IncC and IncA conjugative plasmids. SGI1 hijacks the plasmid conjugation apparatus to be mobilized. However, these mobile elements are incompatible in a bacterial population. This incompatibility is caused by SGI1 transient replication that involves, besides IncC/IncA factors, the SGI1 transcriptional activators sgaDC (1, 2). SgaDC are functional homologues of the IncC master activator AcaCD proteins. Unlike acaCD, the regulation of sgaCD expression has not been characterized yet.The identification of LexA binding motifs on SGI1, especially in the putative promoter region of sgaDC, suggested it may constitute a SOS response-regulated region. Moreover, plasmid entry by conjugation as single-strand DNA in recipient bacteria is known to transiently activate the SOS response (3). Therefore, in the present study we assessed whether the entry of an IncC plasmid by conjugation could lead to transient activation of the SOS response, resulting in the sgaDC expression and other SGI1 genes under its control. We performed β-galactosidase reporter assay to quantify the SOS response activation by IncC/IncA plasmids in transconjugant cells during conjugation based on a previously described method (3). that the IncC conjugative entry activates the SOS response. Through different molecular experiments (β-galactosidase assays, EMSAs, RT-qPCR), we confirmed that the LexA binding site in the sgaDC promoter region is functional, resulting in the control of its expression by the SOS response. Subsequently, several SGI1 genes implicated in its transfer and maintenance are induced in a SgaDC-dependent manner. Finally, we developed an original tripartite conjugation assay to decipher the role of the SOS response in the chronology of the SGI1 conjugative transfer and hijacking of the IncC conjugation system. References:1. Huguet,K.T., Rivard,N., Garneau,D., Palanee,J. and Burrus,V. (2020) Replication of the Salmonella Genomic Island 1 (SGI1) triggered by helper IncC conjugative plasmids promotes incompatibility and plasmid loss. PLoS Genet., 16, 1–22.2. Szabó,M., Murányi,G. and Kiss,J. (2021) IncC helper dependent plasmid-like replication of Salmonella Genomic Island 1. Nucleic Acids Res., 49, 832–846.3. Baharoglu,Z., Bikard,D. and Mazel,D. (2010) Conjugative DNA transfer induces the bacterial SOS response and promotes antibiotic resistance development through integron activation. PLoS Genet., 6, 1–10.