A Novel Integrative Conjugative Element Mediates Genetic Transfer from Group G Streptococcus to Other β-Hemolytic Streptococci

Abstract

Lateral gene transfer is a significant contributor to the ongoing evolution of many bacterial pathogens, including ␤-hemolytic streptococci. Here we provide the first characterization of a novel integrative conjugative element (ICE), ICESde3396, from Streptococcus dysgalactiae subsp. equisimilis (group G streptococcus [GGS]), a bacterium commonly found in the throat and skin of humans. ICESde3396 is 64 kb in size and encodes 66 putative open reading frames. ICESde3396 shares 38 open reading frames with a putative ICE from Streptococcus agalactiae (group B streptococcus [GBS]), ICESa2603. In addition to genes involves in conjugal processes, ICESde3396 also carries genes predicted to be involved in virulence and resistance to various metals. A major feature of ICESde3396 differentiating it from ICESa2603 is the presence of an 18-kb internal recombinogenic region containing four unique gene clusters, which appear to have been acquired from streptococcal and nonstreptococcal bacterial species. The four clusters include two cadmium resistance operons, an arsenic resistance operon, and genes with orthologues in a group A streptococcus (GAS) prophage. Streptococci that naturally harbor ICESde3396 have increased resistance to cadmium and arsenate, indicating the functionality of genes present in the 18-kb recombinogenic region. By marking ICESde3396 with a kanamycin resistance gene, we demonstrate that the ICE is transferable to other GGS isolates as well as GBS and GAS. To investigate the presence of the ICE in clinical streptococcal isolates, we screened 69 isolates (30 GGS, 19 GBS, and 20 GAS isolates) for the presence of three separate regions of ICESde3396. Eleven isolates possessed all three regions, suggesting they harbored ICESde3396-like elements. Another four isolates possessed ICESa2603-like elements. We propose that ICESde3396 is a mobile genetic element that is capable of acquiring DNA from multiple bacterial sources and is a vehicle for dissemination of this DNA through the wider ␤-hemolytic streptococcal population.

Virulence Gene Pool Detected in Bovine Group C Streptococcus dysgalactiae subsp. dysgalactiae Isolates by Use of a Group A S. pyogenes Virulence Microarray

“…The bovine GCS and human GAS isolates shared 23% of all genes, and both the human GCS/GGS and GAS isolates shared 39% of all genes. A higher content of GAS virulence genes in human GGC/GGS isolates was expected, since both species share the same tissue niche in humans and cause similar spectra of diseases (11,22,58). Nevertheless, and most interestingly, none of the 13 bacteriophage virulence-related genes, all associated with GAS disease, were detected in the human GCS/GGS isolates.…”

ICE Slu van, a 94-Kilobase Mosaic Integrative Conjugative Element Conferring Interspecies Transfer of VanB-Type Glycopeptide Resistance, a Novel Bacitracin Resistance Locus, and a Toxin-Antitoxin Stabilization System

“…equisimilis NS3396 (49). Furthermore, ICESluvan ORF1 to -3, ORF14, ORF69, and ORF75 to -86 showed similarities to ORFs from three non-beta-hemolytic streptococci, Streptococcus pneumoniae, S. suis, and Streptococcus mitis.…”

“…A mosaic pattern was also observed for ICESde3396, which is a montage of genes derived from group A, B, and G Streptococcus organisms, in addition to genes acquired from nonstreptococcal Gram-positive bacteria, such as Listeria innocua and E. faecalis (49).…”

“…A putative transfer system (ORF11 to -16 and ORF79 to -80) (see Table S2 in the supplemental material) was identified in the ICESluvan element, in addition to those encoded by Tn5382/Tn1549 (ORF21 to -23, ORF26, and ORF43 and -44) (see Table S2) (30). ORF11 to -15 were 94 to 99% identical to ICESde3396_59 to ICESde3396_55 (49). The ORFs display the same genetic order in the ICESluvan element and belong to a type IV secretion system.…”

“…The streptococcal ICESde3396 encodes resistance toward cadmium and arsenic (49). These resistance genes were not identified in ICESluvan.…”