RT Journal Article SR Electronic T1 Strand-biased circularizing integrative elements spread tmexCD-toprJ gene clusters encoding RND-type multidrug efflux pumps by repeated transpositions JF bioRxiv FD Cold Spring Harbor Laboratory SP 2022.09.22.508988 DO 10.1101/2022.09.22.508988 A1 Trung Duc Dao A1 Hirokazu Yano A1 Taichiro Takemura A1 Aki Hirabayashi A1 Le Thi Trang A1 Hoang Huy Tran A1 Keigo Shibayama A1 Futoshi Hasebe A1 Ikuro Kasuga A1 Masato Suzuki YR 2022 UL http://biorxiv.org/content/early/2022/09/22/2022.09.22.508988.abstract AB Antimicrobial resistance genes (ARGs) are associated with mobile genetic elements (MGEs) that conscript useful genes into the human–microbe and microbe–microbe battlefields. Thus, under intense selective pressure, ARGs have been constantly adapting and evolving, spreading among microbes. tmexCD-toprJ gene clusters, which encode resistance–nodulation–cell division (RND)-type efflux pumps, confer multidrug-resistance to clinically important antimicrobials, including tigecycline. Noteworthily, these gene clusters have emerged in gram-negative bacteria in humans, animals, and the environment worldwide by MGE-mediated transfer. Here we show a hidden MGE, strand-biased circularizing integrative element (SE), that is recently recognized to mediate transpositions of ARGs, associated with the spread of tmexCD-toprJ gene clusters. We identified multidrug-resistant isolates of Aeromonas species in a water environment in Vietnam that harbored multiple copies of tmexCD-toprJ in their chromosomes that were associated with SEs. In particular, Aeromonas hydrophila NUITM-VA1 was found to harbor two copies of a novel variant of tmexC3.3D3.3-topJ1 within cognate SEs, whereas Aeromonas caviae NUITM-VA2 harbored four copies of a novel variant of tmexC2D2.3-topJ2 within cognate SEs. Based on the nature of SE to incorporate a neighboring sequence into the circular form and reinsert it into target sites during transposition, we identified the order of intragenomic movements of tmexCD-toprJ gene clusters. Altogether, our findings suggest that most known subgroups of tmexCD-toprJ and their subvariants underwent transpositions among bacterial chromosomes and plasmids via SEs. Hence, a tmexCD-toprJ gene cluster ancestor may have been initially mobilized via SE, subsequently spreading among bacteria and evolving in new hosts.Competing Interest StatementThe authors have declared no competing interest.