Siderophore typing, a powerful tool for the identification of fluorescent and nonfluorescent pseudomonads

Abstract

A total of 301 strains of fluorescent pseudomonads previously characterized by conventional phenotypic and/or genomic taxonomic methods were analyzed through siderotyping, i.e., by the isoelectrophoretic characterization of their main siderophores and pyoverdines and determination of the pyoverdine-mediated iron uptake specificity of the strains. As a general rule, strains within a well-circumscribed taxonomic group, namely the species Pseudomonas brassicacearum, Pseudomonas fuscovaginae, Pseudomonas jessenii, Pseudomonas mandelii, Pseudomonas monteilii, "Pseudomonas mosselii," "Pseudomonas palleronii," Pseudomonas rhodesiae, "Pseudomonas salomonii," Pseudomonas syringae, Pseudomonas thivervalensis, Pseudomonas tolaasii, and Pseudomonas veronii and the genomospecies FP1, FP2, and FP3 produced an identical pyoverdine which, in addition, was characteristic of the group, since it was structurally different from the pyoverdines produced by the other groups. In contrast, 28 strains belonging to the notoriously heterogeneous Pseudomonas fluorescens species were characterized by great heterogeneity at the pyoverdine level. The study of 23 partially characterized phenotypic clusters demonstrated that siderotyping is very useful in suggesting correlations between clusters and well-defined species and in detecting misclassified individual strains, as verified by DNA-DNA hybridization. The usefulness of siderotyping as a determinative tool was extended to the nonfluorescent species Pseudomonas corrugata, Pseudomonas frederiksbergensis, Pseudomonas graminis, and Pseudomonas plecoglossicida, which were seen to have an identical species-specific siderophore system and thus were easily differentiated from one another. Thus, the fast, accurate, and easy-to-perform siderotyping method compares favorably with the usual phenotypic and genomic methods presently necessary for accurate identification of pseudomonads at the species level.

FIG. 1.

Structure of the iron complex of the P. aeruginosa ATCC 27853 pyoverdine. The acyl chain (R group) could be succinic acid, succinamide, or glutamic acid (44).

FIG. 2.

Isoelectrophoretic patterns of the pyoverdine isoforms produced by (from left to right) P. syringae ATCC 19310^T, P. syringae CFBP 2106, strain C-TR1015 (cluster C9), P. monteilii CFML 90-54, P. rhodesiae CFML 92-104, P. tolaasii CFBP 2068^T, P. mandelii CFML 95-303^T, strain CFML 96-338 (cluster XXXIIb), the strain CFML 96-299 (cluster XXXIIb). The last lane contained an internal standard for pI measurement (18).