Quaternary ammonium disinfectants catalyze transposition on promiscuous conjugative plasmids in Pseudomonas spp

Transposable elements (TEs) are genetic vehicles that play a pivotal role in bacterial genome evolution due to their autonomous mobility. TEs are especially important for their ability to mobilize genes, including those related to antimicrobial resistance and xenobiotic degradation. Beyond their genomic movement, interaction of TEs with other mobile genetic elements, such as conjugative plasmids, raises concerns about the potential dissemination of resistance genes. The main objective of this study is to evaluate the interaction of TEs with conjugative plasmids when bacteria is exposed to quaternary ammonium disinfectants (QACs). In this study, we used two bacterial strains i.e. Pseudomonas sessilinigenes BIOMIG1BAC and Pseudomonas saponiphila DSM 9751, both of which can degrade QACs and have significant number of TEs in their chromosome. DSM9751 harbor a native conjugative plasmid (p9751) whereas BIOMIG1 has been transformed with pRK24. Both strains were incubated in minimal salt medium containing 200 µg/mL benzalkonium chlorides (BACs) with or without 500 µg/mL acetate. Cultures incubated in only 1000 µg/mL acetate were used as the controls. At the end of 48-hr incubation when the BACs acetate was completely utilized, plasmids were extracted and sequenced. Sequences of plasmids obtained during the transposition experiments were compared with the original sequences of the plasmids and the transposition events were identified. Two major transposition events catalyzed by BACs were identified on p9751 in DSM9751. The first one was excision of IS21 family IS1474 and the other was insertion of IS1380 family ISPa33. pRK24 was under heavy attack of Tn3 family unit transposon carrying merPTR operon. This transposon translocate itself to three different locations on pRK24 in BIOMIG1 resulting in excision of T4SS transfer region of the plasmid. In conclusion, this study showed that conjugative plasmids native to Pseudomonas spp. serve as targets to TEs under the influence of QAC disinfectants. Such transposition events may not only result in horizontal transfer of genes but also genetic diversification of conjugative plasmids.