High-affinity iron uptake systems present in Erwinia carotovora subsp. carotovora include the hydroxamate siderophore aerobactin

Abstract

The phytopathogenic bacterium Erwinia carotovora subsp. carotovora W3C105 produced the hydroxamate siderophore aerobactin under iron-limiting conditions. A survey of 22 diverse strains of E. carotovora revealed that strain W3C105 alone produced aerobactin. The ferric-aerobactin receptor of strain W3C105 was an 80-kDa protein, identified by immunoblots of Sarkosyl-soluble proteins obtained from E. carotovora cells grown in iron-depleted medium and probed with antiserum raised against the 74-kDa ferric-aerobactin receptor encoded by the pColV-K30 plasmid of Escherichia coli. Genes determining aerobactin biosynthesis and uptake were localized to an 11.3-kb EcoRI-HindIII chromosomal fragment of strain W3C105. A 10-kb subclone of the fragment conferred on E. coli DH5 alpha both aerobactin biosynthesis and uptake, determined by cloacin DF13 sensitivity, the presence of the 80-kDa receptor protein, and iron-independent growth of E. coli clones. The aerobactin biosynthesis genes of E. carotovora W3C105 hybridized to those of the pColV-K30 plasmid of E. coli, but the restriction patterns of the aerobactin regions of E. coli and E. carotovora differed. Although the aerobactin region of enteric bacteria is commonly flanked by IS1-like sequences, IS1 sequences were not detected in the genomic DNA or the cloned aerobactin region of E. carotovora. E. coli DH5 alpha cells harboring cloned aerobactin biosynthesis genes from E. carotovora W3C105 produced greater quantities of aerobactin and the 80-kDa ferric-aerobactin receptor when grown in iron-limited than in iron-replete medium. Strain W3C105 grew on an iron-limited medium, whereas derivatives that lacked a functional aerobactin iron acquisition system did not grow on the medium. These results provide evidence for the occurrence and heterogeneity of aerobactin as a high-affinity iron uptake system of both clinical and phytopathogenic species of the Enterobacteriaceae. Although future studies may reveal a role for aerobactin in the virulence or ecology of strain W3C105, a functional aerobactin iron acquisition system is not necessary for the pathogenicity of E. carotovora.

Siderophore-Mediated Iron Acquisition Influences Motility and Is Required for Full Virulence of the Xylem-Dwelling Bacterial Phytopathogen Pantoea stewartii subsp. stewartii

“…A number of other plant pathogens produce siderophores that do not have an apparent role in host colonization. For example, there is no distinct correlation between aerobactin production and virulence in Erwinia carotovora where mutants lacking aerobactin biosynthetic functions were still able to cause soft rot symptoms on potato (22). Pseudomonas syringae pv.…”

“…The presence of the aerobactin biosynthetic operon is also correlated with high levels of virulence in extraintestinal pathogenic E. coli strains often found in livestock (12). The plant pathogen Pectobacterium carotovorum can synthesize aerobactin as well, but it is only found in a minority of P. carotovorum strains, and its function is dispensable for pathogenicity (22). Analysis of the P. stewartii genome indicates the presence of a conserved iucABCD-iutA operon in P. stewartii (23).…”

The impact of transition metals on bacterial plant disease

“…Erwinia carotovora (now Pectobacterium carotovorum) produces the high-affinity hydroxamate siderophore, aerobactin (Ishimaru & Loper, 1992), and a high-affinity class of siderophores, desferriodoxamines, is conserved among Erwinia and Pantoea species (Smits & Duffy, 2011). Erwinia carotovora (now Pectobacterium carotovorum) produces the high-affinity hydroxamate siderophore, aerobactin (Ishimaru & Loper, 1992), and a high-affinity class of siderophores, desferriodoxamines, is conserved among Erwinia and Pantoea species (Smits & Duffy, 2011).…”

Iron assimilation storage in prokaryotes

“…Erwinia carotovora subsp. carotovora W3C105 has recently been shown to produce aerobactin and a ferric aerobactin receptor encoded by a chromosomal fragment; however, a functional aerobactin acquisition system is not necessary for the pathogenicity of this bacterium (Ishimaru & Loper, 1992).…”