AUTHOR=Santoro Francesco , Romeo Alessandra , Pozzi Gianni , Iannelli Francesco 

TITLE=Excision and Circularization of Integrative Conjugative Element Tn5253 of Streptococcus pneumoniae

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.01779

DOI=10.3389/fmicb.2018.01779

ISSN=1664-302X

ABSTRACT=<p>The integrative conjugative element (ICE) Tn<italic>5253</italic> of <italic>Streptococcus pneumoniae</italic>, conferring resistance to tetracycline and chloramphenicol, was found integrated at a 83-bp specific target site (<italic>att</italic>B) located in the <italic>rbgA</italic> gene of the pneumococcal chromosome. PCR analysis of Tn<italic>5253</italic>-carrying strains showed evidence of precise excision of Tn<italic>5253</italic> from the pneumococcal chromosome with production of (i) circular forms of the ICE in which the ends were joined by a 84-bp sequence (<italic>att</italic>Tn), and (ii) reconstituted chromosomal <italic>att</italic>B. When integrated into the chromosome, Tn<italic>5253</italic> was flanked by <italic>att</italic>L, identical to <italic>att</italic>B, and <italic>att</italic>R, identical to <italic>att</italic>Tn. Circular forms of Tn<italic>5253</italic> were present at a concentration of 3.8 × 10<sup>-4</sup> copies per chromosome, whereas reconstituted <italic>att</italic>B sites were at 3.0 × 10<sup>-4</sup> copies per chromosome. Deletion of <italic>int-xis</italic> of Tn<italic>5253</italic> abolished production of circular forms (&lt;7.1 × 10<sup>-6</sup> copies per chromosome) and was associated to the lack of Tn<italic>5253</italic> conjugal transfer suggesting, as expected, that Tn<italic>5253</italic> circular form acts as a conjugation intermediate.</p>