The Irp9 protein of Yersinia enterocolitica participates in the synthesis of salicylate, the precursor of the siderophore yersiniabactin. In Pseudomonas species, salicylate synthesis is mediated by two enzymes: isochorismate synthase and isochorismate pyruvate-lyase. Both enzymes are required for complementation of a Yersinia irp9 mutant. However, irp9 is not able to complement Escherichia coli entC for the production of enterobactin, which requires isochorismate as a precursor. These results suggest that Irp9 directly converts chorismate into salicylate.

Salmonellaspp. are enteropathogenic gram-negative bacteria that use a large array of virulence factors to colonize the host, manipulate host cells, and resist the host's defense mechanisms. Even closely relatedSalmonellastrains have different repertoires of virulence factors. Bacteriophages contribute substantially to this diversity. There is increasing evidence that the reassortment of virulence factor repertoires by converting phages like the GIFSY phages and SopEΦ may represent an important mechanism in the adaptation ofSalmonellaspp. to specific hosts and to the emergence of new epidemic strains. Here, we have analyzed in more detail SopEΦ, a P2-like phage fromSalmonella entericaserovar Typhimurium DT204 that encodes the virulence factor SopE. We have cloned and characterized the attachment site (att) of SopEΦ and found that its 47-bp core sequence overlaps the 3′ terminus of thessrAgene of serovar Typhimurium. Furthermore, we have demonstrated integration of SopEΦ into the clonedattBsite of serovar Typhimurium A36. Sequence analysis of the plasmid-borne prophage revealed that SopEΦ is closely related to (60 to 100% identity over 80% of the genome) but clearly distinct from the Fels-2 prophage of serovar Typhimurium LT2 and from P2-like phages in the serovar Typhi CT18 genome. Our results demonstrate that there is considerable variation among the P2-like phages present in closely relatedSalmonellaspp.

Yersinia enterocolitica O:8, biogroup (BG) IB, strain WA-C carries a high-pathogenicity island (HPI) including iron-repressible genes (irp1–9, fyuA) for biosynthesis and uptake of the siderophore yersiniabactin (Ybt). The authors report the functional analysis of irp6,7,8, which show 98–99% similarity to the corresponding genes ybtP,Q,X on the HPI of Yersinia pestis. It was demonstrated that irp6,7 are involved in ferric (Fe)-Ybt utilization and mouse virulence of Y. enterocolitica, thus confirming corresponding results for Y. pestis. Additionally it was shown that inactivation of the ampG-like gene irp8 did not affect either Fe-Ybt utilization or mouse virulence. To determine whether irp6, irp7 and fyuA (encoding the outer-membrane Fe-Ybt/pesticin receptor FyuA) are sufficient to mediate Fe-Ybt transport/utilization, these genes were transferred into Escherichia coli entD,F and into non-pathogenic Y. enterocolitica, BG IA, strain NF-O. Surprisingly, E. coli entD,F but not Y. enterocolitica NF-O gained the capability to utilize exogenous Fe-Ybt as a result of this gene transfer, although both strains expressed functional FyuA (pesticin sensitivity). These results suggest that besides irp6, irp7 and fyuA, additional genes are required for sufficient Fe-Ybt transport/utilization. Finally, it was shown that irp6, irp7 and fyuA but not irp8 are involved in controlling Ybt biosynthesis and fyuA gene expression: irp6 and/or irp7 mutation leads to upregulation whereas fyuA mutation leads to downregulation. However, fyuA-dependent control of Ybt biosynthesis could be bypassed in a fyuA mutant by ingredients of chrome azurol S (CAS) siderophore indicator agar.

In light of public concerns over the use of pesticides and antibiotics in plant protection and the subsequent selection for spread of resistant bacteria in the environment, it is inevitable to broaden our knowledge about viable alternatives, such as natural antagonists and their mode of action. The genus Pseudomonas is known for its metabolic versatility and genetic plasticity, encompassing pathogens as well as antagonists. We characterized strain Pseudomonas orientalis F9, an isolate from apple flowers in a Swiss orchard, and determined its antagonistic activity against several phytopathogenic bacteria, in particular Erwinia amylovora, the causal agent of fire blight. P. orientalis F9 displayed antagonistic activity against a broad suite of phytopathogenic bacteria in the in vitro tests. The promising results from this analysis led to an ex vivo assay with E. amylovora CFBP1430^Rif and P. orientalis F9 infected detached apple flowers. F9 diminished the fire blight pathogen in the flowers but also revealed phytotoxic traits. The experimental results were discussed in light of the complete genome sequence of F9, which revealed the strain to carry phenazine genes. Phenazines are known to contribute to antagonistic activity of bacterial strains against soil pathogens. When tested in the cress assay with Pythium ultimum as pathogen, F9 showed results comparable to the known antagonist P. protegens CHA0.

Pseudomonas citronellolis is a Gram negative, motile gammaproteobacterium belonging to the order Pseudomonadales and the family Pseudomonadaceae. We isolated strain P3B5 from the phyllosphere of basil plants (Ocimum basilicum L.). Here we describe the physiology of this microorganism, its full genome sequence, and detailed annotation. The 6.95 Mbp genome contains 6071 predicted protein coding sequences and 96 RNA coding sequences. P. citronellolis has been the subject of many studies including the investigation of long-chain aliphatic compounds and terpene degradation. Plant leaves are covered by long-chain aliphates making up a waxy layer that is associated with the leaf cuticle. In addition, basil leaves are known to contain high amounts of terpenoid substances, hinting to a potential nutrient niche that might be exploited by P. citronellolis. Furthermore, the isolated strain exhibited resistance to several antibiotics. To evaluate the potential of this strain as source of transferable antibiotic resistance genes on raw consumed herbs we therefore investigated if those resistances are encoded on mobile genetic elements. The availability of the genome will be helpful for comparative genomics of the phylogenetically broad pseudomonads, in particular with the sequence of the P. citronellolis type strain PRJDB205 not yet publicly available. The genome is discussed with respect to a phyllosphere related lifestyle, aliphate and terpenoid degradation, and antibiotic resistance.