Plasmid-Encoded Iron Uptake Systems

Abstract

Plasmids confer genetic information that benefits the bacterial cells containing them. In pathogenic bacteria, plasmids often harbor virulence determinants that enhance the pathogenicity of the bacterium. The ability to acquire iron in environments where it is limited, for instance the eukaryotic host, is a critical factor for bacterial growth. To acquire iron, bacteria have evolved specific iron uptake mechanisms. These systems are often chromosomally encoded, while those that are plasmid-encoded are rare. Two main plasmid types, ColV and pJM1, have been shown to harbor determinants that increase virulence by providing the cell with essential iron for growth. It is clear that these two plasmid groups evolved independently from each other since they do not share similarities either in the plasmid backbones or in the iron uptake systems they harbor. The siderophores aerobactin and salmochelin that are found on ColV plasmids fall in the hydroxamate and catechol group, respectively, whereas both functional groups are present in the anguibactin siderophore, the only iron uptake system found on pJM1-type plasmids. Besides siderophore-mediated iron uptake, ColV plasmids carry additional genes involved in iron metabolism. These systems include ABC transporters, hemolysins, and a hemoglobin protease. ColV-and pJM1-like plasmids have been shown to confer virulence to their bacterial host, and this trait can be completely ascribed to their encoded iron uptake systems.

Identification of Potential Virulence Factors in the Model Strain Acinetobacter baumannii A118

“…Consequently, bacteria have evolved very efficient iron-acquisition systems to scavenge iron from the iron-binding proteins of their hosts. These systems are varied and include synthesis of a siderophore (a high-affinity ferric iron chelator) that uptakes iron and mediates its internalization through a specific energy-dependent transport system (Crosa and Walsh, 2002; Di Lorenzo and Stork, 2014; Li and Ma, 2017), production of outer membrane receptors that recognize lactoferrin, transferrin, heme or non-indigenous siderophores (Koster, 2005; Antunes et al, 2011; Di Lorenzo and Stork, 2014; Huang and Wilks, 2017), or direct binding and transport of ferrous iron (Lau et al, 2016). The siderophore-mediated iron uptake systems identified in A. baumannii strains are those that utilize acinetobactin (Echenique et al, 1992; Actis et al, 1993, 1999), baumannoferrin (Penwell et al, 2015), or fimsbactins, which are represented by a family of six related chatechol/hydroxamate compounds (Proschak et al, 2013).…”

Comparative Genome Analyses of Vibrio anguillarum Strains Reveal a Link with Pathogenicity Traits

“…Although the mechanism of pathogenesis of V. anguillarum is not completely understood, virulence-related factors have been identified and include chemotaxis and motility ( 10 , 11 ), adhesion ( 12 ), invasion ( 13 , 14 ), iron sequestration ( 15 , 16 ), and secretion of extracellular enzymes ( 17 , 18 ). Several putative virulence genes have been detected in the genome of V. anguillarum strain H775-3 (the pJM1-cured strain of 775), including genes encoding exotoxins, adherence/colonization factors, invasion, capsule and cell surface components, and an iron uptake system ( 19 , 20 ).…”

Expression of IroN, the salmochelin siderophore receptor, requires mRNA activation by RyhB small RNA homologues

“…While chromosomally located in all Salmonella enterica lineages (Bäumler et al ., ) and in uropathogenic Escherichia coli (Welch et al ., ), the iroBCDE‐iroN gene cluster is also present in transmissible plasmids found in Escherichia coli , Enterobacter and in hyper‐virulent isolates of Klebsiella pneumoniae (Sorsa et al ., ; Di Lorenzo and Stork, ; Struve et al ., ). These findings underscore the relevance of this iron utilization system as a virulence determinant and corroborate the notion that it is acquired through horizontal transfer.…”