Plasmid Capture by the Bacillus thuringiensis Conjugative Plasmid pXO16

Abstract

Conjugation, mobilization, and retromobilization are three related mechanisms of horizontal gene transfer in bacteria. They have been extensively studied in gram-negative species, where retromobilization, the capture of DNA from a recipient by a donor cell, was shown to result from two successive steps: the transfer of the conjugative plasmid from the donor to the recipient followed by the retrotransfer of the mobilizable plasmid to the donor. This successive model was established for gram-negative bacteria but was lacking experimental data from the gram-positive counterparts. In the present work, the mobilization and retromobilization abilities of the conjugative plasmid pXO16 from Bacillus thuringiensis subsp. israelensis were studied using the mobilizable plasmids pUB110 and pE194 and the "nonmobilizable" element pC194 lacking the mob and oriT features (all from Staphylococcus aureus). Experimental data suggested a successive model, since different retromobilization frequencies were observed between the small plasmids. More importantly, retromobilization was shown to be delayed by 50 and 150 min for pUB110 and pE194, respectively, compared to pXO16 conjugation. Natural liquid foods (cow milk, soy milk, and rice milk) were used to evaluate the putative ecological impact of these transfers. In cow and soy milk, conjugation, mobilization, and retromobilization were shown to occur at frequencies of 8.0 ؋ 10 ؊1 , 1.0 ؋ 10 ؊2 , and 1.2 ؋ 10 ؊4 transconjugants per recipient, respectively. These data are comparable to those obtained with LB medium and about 10-fold lower than in the case of rice milk. Taken together, these results emphasize the potential role of plasmid capture played by B. thuringiensis in natural environments.

pXO16 from Bacillus thuringiensis serovar israelensis: Almost 350 kb of terra incognita

“…Beside its own transfer, the conjugative system of pXO16 is also able to mobilize and retro-mobilize many plasmids, including those lacking mob and oriT regions Timmery et al, 2009). The retro-mobilization mechanism follows a "successive" model, meaning that pXO16 has to transfer itself first into a recipient cell before it can "retro-mobilize" a plasmid from this recipient to the donor bacteria (Timmery et al, 2009).…”

“…The retro-mobilization mechanism follows a "successive" model, meaning that pXO16 has to transfer itself first into a recipient cell before it can "retro-mobilize" a plasmid from this recipient to the donor bacteria (Timmery et al, 2009).…”

Conjugation in Bacillus thuringiensis: Insights into the Plasmids Exchange Process

“…However, Timmery et al (2009) also demonstrated the retromobilization abilities of the conjugative plasmid pXO16 of B. thuringiensis subsp. israelensis, which were compared with the conjugation and mobilization abilities of this plasmid using mobilizable plasmids and a nonmobilizable element lacking the mob gene and oriT site.…”

“…Two different systems were described: the classical triparental matings are made using a donor, a recipient and a helper strain, which can transfer a mobilizable plasmid or a nonmobilizable plasmid, as detected by Timmery et al (2009). In this system transfer of a conjugative plasmid from the donor to the recipient and to the helper strain may occur as well as, mobilization of the plasmid from the helper strain to the recipient, transfer of both plasmids to the recipient, and retromobilization of the plasmid from the helper strain to the donor.…”

Evolutionary aspects of toxin-producing bacteria

“…Selective pressure and HGT, combined with recombination and shuffling between toxin genes (resulting in domain swapping) and sequence divergence, has yielded a wide range of host specificities for these insecticidal toxins [235,[285][286][287]. The genes encoding the crystal protein toxins, for example, are frequently clustered on different transmissible plasmids or transposable elements [235,[285][286][287][288], and conjugation between different strains has been observed in the soil environment and within insect guts [289][290][291][292]. Individual toxins have insecticidal activity only against a limited range of insect species (i.e., usually only within certain insect orders).…”