6). PFGI-1 does not encode a Rep protein, and it is not clear whether it replicates by a theta-type or strand displacement mechanism, although the latter has been suggested for pKLC102 [30]. Like some conjugative plasmids, PFGI-1 carries homologues of the stress-inducible genes umuC (PFL_4692) and umuD (PFL_4691), which encode a putative lesion bypass DNA polymerase and a related accessory protein,

respectively. Such genes may be involved in plasmid DNA repair and umuDC-mediated mutagenesis, which could allow plasmids to adapt more quickly to new bacterial hosts [41]. PFGI-1 also contains a cluster of 10 genes, pilLNOPQRSTUVM (PFL_4675 through PFL_4683) (Fig. 6), that spans over 10 kb and Selleck RSL 3 closely resembles part of the pil region from the self-transmissible E. coli plasmid R64 [42]. In E. coli, these genes are involved in production of thin flexible sex pili required for mating and transfer of R64 in liquid media. The similarity between the pil clusters of R64 and PFGI-1 suggests that the latter encode mating pili rather than type IV pili involved in bacterial twitching motility, adherence to host cells, biofilm formation and phage sensitivity [43]. P. Barasertib price fluorescens Pf-5 has the capaCity to produce type IV pili,

and the corresponding biosynthetic genes are located in at least three clusters found outside of PFGI-1. The PFGI-1 ITF2357 pil cluster contains genes for pilin protein PilS (PFL_4680), prepilin peptidase PilU (PFL_4681), outer membrane protein PilN (PFL_4676), nucleotide binding protein PilQ (PFL_4678), integral membrane protein PilR (PFL_4679), and pilus adhesin PilV (PFL_4682). Unlike R64, PFGI-1 does not include a shufflon PIK3C2G region that determines recipient specifiCity in liquid matings via generation of different adhesin types [42, 44]. Finally, PFGI-1 carries genes

encoding proteins that may be involved in conjugal DNA transfer. PFL_4696 and PFL_4706 encode for TraG-like coupling proteins that may function as membrane-associated NTPases, which during conjugation would mediate transport of DNA covalently linked to a putative relaxase protein (the product of PFL_4751). Recent studies have demonstrated that ICEs are a major component of a flexible gene pool of different lineages of Gram-negative Proteobacteria [45–47]. Metabolically versatile members of the Pseudomonadaceae are no exception, with ICEs having been identified among strains of P. aeruginosa [29–32], P. syringae [36, 48], and P. fluorescens [49]. Comparison of PFGI-1 with islands from other Pseudomonas spp. reveals at least six highly conserved gene clusters (Fig. 7).