Mobilization of IMEs Integrated in the oriT of ICEs Involves Their Own Relaxase Belonging to the Rep-Trans Family of Proteins

Abstract

Integrative mobilizable elements (IMEs) are widespread but very poorly studied integrated elements that can excise and hijack the transfer apparatus of co-resident conjugative elements to promote their own spreading. Sixty-four putative IMEs, harboring closely related mobilization and recombination modules, were found in 14 Streptococcus species and in Staphylococcus aureus. Fifty-three are integrated into the origin of transfer (oriT) of a host integrative conjugative element (ICE), encoding a MobT relaxase and belonging to three distant families: ICESt3, Tn916, and ICE6013. The others are integrated into an unrelated IME or in chromosomal sites. After labeling by an antibiotic resistance gene, the conjugative transfer of one of these IMEs (named IME_oriTs) and its host ICE was measured. Although the IME is integrated in an ICE, it does not transfer as a part of the host ICE (no cis-mobilization). The IME excises and transfers separately from the ICE (without impacting its transfer rate) using its own relaxase, distantly related to all known MobT relaxases, and integrates in the oriT of the ICE after transfer. Overall, IME_oriTs use MobT-encoding ICEs both as hosts and as helpers for conjugative transfer. As half of them carry lsa(C), they actively participate in the dissemination of lincosamide–streptogramin A–pleuromutilin resistance among Firmicutes.

Hijackers, hitchhikers, or co-drivers? The mysteries of microbial mobilizable genetic elements

“…A different process is someemes observed in phages and satellites (and even in conjugaeve elements): some HGEs integrate their helpers aper transfer. For example, some satellites were observed to integrate within prophages (62), and some IMEs within ICEs (30). These processes are different from conduceon because the co-integrate is split before transfer and the two elements are transferred independently.…”

“…These processes are different from conduceon because the co-integrate is split before transfer and the two elements are transferred independently. Nevertheless, they can also provide informaeon on the compaebility of helpers and hitchers, since available data suggests that co-integraeon allows the HGE to take control of the transmission of their helper (30). Hence, co-integraeon of hitcher and helper provides strong evidence that the two are a compaeble pair, i.e.…”

“…For instance, the satellites cfPICI EcClEDL933 (15) and PICMI115 (17) had no significant effect on the produceon of the viral parecles carrying the DNA of their helpers. Similarly, integraeve elements mobilized by ICEs related to ICESt3 (78), as well as plasmids mobilized by the conjugaeve plasmid pWBG749 (79), have a negligible impact in the efficiency of transfer of their helpers. Nevertheless, the cost of hitcher mobilizaeon to its helpers probably depends on the hitcher and on the helpers.…”

Prevalence and mobility of integrative and conjugative elements within a Streptomyces natural population

“…Closely related elements are Integrated and Mobilizable Elements (IMEs) that use similar excision and integration strategies but with non-related relaxases and coupling proteins. Their transfer is dependent upon a T4SS hijacked from another conjugative element ( Libante et al, 2020 ).…”