Analysis and identification of IS1548insertion targets inStreptococcus agalactiae

Abstract

The prevalence of the insertion sequence IS1548 is strongly linked to clonal complex 19 Streptococcus agalactiae strains associated with neonatal meningitis and endocarditis. We previously reported that IS1548 insertion upstream of lmb is involved in stronger binding of a S. agalactiae meningitic strain to laminin. A few other IS1548 insertion sites were also identified by others. In this study, we analyzed IS1548 described target sites in S. agalactiae and showed that most of them are linked to zinc-responsive genes. Moreover, we identified two not yet described IS1548 insertion sites in the adcRCB operon encoding the main regulator of zinc homeostasis and subunits of a zinc ABC transporter. We also identified two conserved motifs of 8 and 10 bp close to IS1548 insertion sites. These motifs representing potential IS1548 targets were found upstream of several S. agalactiae ORFs. One of these predicted IS1548 targets was validated experimentally, allowing the identification of an IS1548 insertion site upstream of murB in all of the clonal complex 19 strains tested. The possible effects of these insertions on the virulence of the strains are discussed.

Physiological impact of transposable elements encoding DDE transposases in the environmental adaptation of Streptococcus agalactiae

“…We previously identified two conserved motifs close to IS 1548 insertion sites. Interestingly, these motifs representing potential IS 1548 targets are both present in the covS region of S. agalactiae , suggesting that this gene might also be targeted by IS 1548 in this species (Fléchard et al , 2013a).…”

“…We propose that IS 1548 may also modulate metal homeostasis in S. agalactiae . Indeed, we recently identified two IS 1548 integration sites in the adcRCB operon encoding the zinc-dependent AdcR repressor, and the ATPase and permease subunits of a putative zinc/manganese ABC transporter (Fléchard et al , 2013a). We also identified an IS 1548 insertion in a region very close to and upstream of adcA , encoding the high affinity zinc-binding protein of the Adc transporter (Fléchard et al , 2013b).…”

“…Moreover, the laminin-binding protein Lmb, encoded by a gene that is one of the preferential targets of IS 1548 in S. agalactiae , exhibits significant homologies to AdcA, and was shown to bind a zinc divalent cation in S. agalactiae (Granlund et al , 1998, 2001; Ragunathan et al , 2009). Furthermore, IS 1548 insertions identified within the adcRCB operon spontaneously appeared during growth in vitro , suggesting, as is the case with covS , that a bacterial subpopulation carrying the mutation could emerge during the infectious process (Fléchard et al , 2013a). This subpopulation might expand in the presence of selective pressure, which could be the local zinc concentration.…”

“…Indeed, during S. agalactiae invasive infections, the bacteria cross successively anatomical sites and fluids with greatly varying zinc concentrations. The possibility of modulating the expression of zinc transporters by the dynamic insertion of IS 1548 may confer an adaptive advantage to S. agalactiae allowing the ‘success’ of its infection (Fléchard et al , 2013a). Furthermore, the IS 1548 covS target described above is also the principal sensor for extracellular Mg 2+ in S. pyogenes , another divalent metallic cation (Gryllos et al , 2007).…”

Natural Mutations in Streptococcus agalactiae Resulting in Abrogation of β Antigen Production

“…Interestingly, the virulence genes or DNA regions associated with the control of virulent properties of S . agalactiae are frequent targets for insertion sequences such as IS 1548 , IS Sa4 and IS 1381 [ 39 – 43 ]. In particular, one of the IS 1381 copies was found to be integrated in the bac gene [ 44 ].…”