Plasmid-like replication of a minimal streptococcal integrative and conjugative element

Abstract

Integrative and conjugative elements (ICEs) are mobile genetic elements encoding their own excision from a replicon of their bacterial host, transfer by conjugation to a recipient bacterium and reintegration for maintenance. The conjugation, recombination and regulation modules of ICEs of the ICESt3 family are grouped together in a region called the ICE 'core region'. In addition to this core region, elements belonging to this family carry a highly variable region including cargo genes that could be involved in bacterial adaptation or in the maintenance of the element. Although ICEs are a major class of mobile elements through bacterial genomes, the functionality of an element encoding only its excision, transfer, integration and regulation has never been demonstrated experimentally. We engineered MiniICESt3, an artificial ICE derived from ICESt3, devoid of its cargo genes and thus only harbouring the core region. The functionality of this minimal element was assessed. MiniICESt3 was found to be able to excise at a rate of 3.1 %, transfer with a frequency of 1.0610 25 transconjugants per donor cell and stably maintain by site-specific integration into the 39 end of the fda gene, the same as ICESt3. Furthermore, MiniICESt3 was found in ,10 copies per chromosome, this multicopy state likely contributing to its stability for .100 generations even in the absence of selection. Therefore, although ICEs were primarily assumed to only replicate along with the chromosome, our results uncovered extrachromosomal rolling-circle replicating plasmid-like forms of MiniICESt3.

Diversity of Integrative and Conjugative Elements of Streptococcus salivarius and Their Intra- and Interspecies Transfer

“…Two-thirds (13/19 if including ICESt3 [35]) of the ICEs analyzed in this work carry a restriction-modification (RM) system (n ϭ 6) or an orphan methyltransferase (n ϭ 7) (Fig. 1).…”

Chromosomal Conjugative and Mobilizable Elements in Streptococcus suis: Major Actors in the Spreading of Antimicrobial Resistance and Bacteriocin Synthesis Genes

“…PCR amplifications were done to detect left (attL) and right (attR) MGEs borders, the attI site of the circular form of the MGEs and the empty chromosomal integration site attB as described previously [54] (see Table S2 for primers used).…”

The Obscure World of Integrative and Mobilizable Elements, Highly Widespread Elements that Pirate Bacterial Conjugative Systems

“…For tandems of functional elements, which encode integrases that share similar specificities but are generally distantly related, it is probable that an incoming element has integrated within the att site of a resident element. However, a scenario involving the acquisition by excision, conjugative transfer and integration of the whole composite element resulting from a former accretion (ICE-IME, IME1-IME2 or CIME-IME) cannot be excluded, since conjugative transfers of CIME-ICE tandems were also observed [ 45 , 80 , 81 , 82 , 83 ]. Such tandem structures can have complex excision patterns [ 12 ].…”