Abstract
The rulAB operon of Pseudomonas spp. confers fitness traits on the host and has been suggested to be a hotspot for insertion of mobile elements that carry avirulence genes. Here, for the first time, we show that rulB on plasmid pWW0 is a hotspot for the active site-specific integration of related integron-like elements (ILEs) found in six environmental pseudomonads (strains FH1–FH6). Integration into rulB on pWW0 occurred at position 6488 generating a 3 bp direct repeat. ILEs from FH1 and FH5 were 9403 bp in length and contained eight open reading frames (ORFs), while the ILE from FH4 was 16 233 bp in length and contained 16 ORFs. In all three ILEs, the first 5.1 kb (containing ORFs 1–4) were structurally conserved and contained three predicted site-specific recombinases/integrases and a tetR homologue. Downstream of these resided ORFs of the ‘variable side’ with structural and sequence similarity to those encoding survival traits on the fitness enhancing plasmid pGRT1 (ILEFH1 and ILEFH5) and the NR-II virulence region of genomic island PAGI-5 (ILEFH4). Collectively, these ILEs share features with the previously described type III protein secretion system effector ILEs and are considered important to host survival and transfer of fitness enhancing and (a)virulence genes between bacteria.
Highlights
Bacteria within the genus Pseudomonas are found in a wide range of terrestrial and aquatic natural and clinical environments and demonstrate remarkable metabolic and physiological versatility including the potential for pathogenicity (Morris et al, 2000; 2007; 2008; Riffaud and Morris, 2002)
We report for the first time the active integration of a group of related integron-like elements (ILEs) from environmental Pseudomonas spp. isolates into plasmid pWW0 and show that insertion into rulAB operon and its homologues in other genera is potentially of key importance to the adaptation and survival of these bacteria
During an investigation of plasmid-encoded copper resistance in environmental pseudomonads recovered in a previous study (Pickup, 1989), we attempted to cure native plasmids from these strains by incompatibility using the IncP-9 toluene-degrading plasmid pWW0
Summary
Bacteria within the genus Pseudomonas are found in a wide range of terrestrial and aquatic natural and clinical environments and demonstrate remarkable metabolic and physiological versatility including the potential for pathogenicity (Morris et al, 2000; 2007; 2008; Riffaud and Morris, 2002) This has been illustrated by sequenced genomes (Rodríguez-Palenzuela et al, 2010; Ortet et al, 2011; Ramírez-Díaz et al, 2011; Winsor et al, 2011; Yu et al, 2011; Patel et al, 2012). The operon is common to both the chromosomes and plasmids of pseudomonads (Sundin et al, 2000; Zhao et al, 2005; Cazorla et al, 2008) In the latter, it is usually located close to transfer or mating pair formation encoding regions in the core backbone, ensuring that it is one of the first regions transferred during conjugation (Gibbon et al, 1999)
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