Pyoverdine synthesis by the Mn(II)-oxidizing bacterium Pseudomonas putida GB-1

Abstract

When iron-starved, the Mn(II)-oxidizing bacteria Pseudomonas putida strains GB-1 and MnB1 produce pyoverdines (PVD GB 1 and PVD ), − MnB1 siderophores that both influence iron uptake and inhibit manganese(II) oxidation by these strains. To explore the properties and genetics of a PVD that can affect manganese oxidation, LC-MS/MS, and various siderotyping techniques were used to identify the peptides of PVD GB−1 and PVD MnB1 as being (for both PVDs): chromophore-Asp-Lys-OHAsp-Ser-Gly-aThr-Lys-cOHOrn, resembling a structure previously reported for P. putida CFML 90-51, which does not oxidize Mn. All three strains also produced an azotobactin and a sulfonated PVD, each with the peptide sequence above, but with unknown regulatory or metabolic effects. Bioinformatic analysis of the sequenced genome of P. putida GB-1 suggested that a particular non-ribosomal peptide synthetase (NRPS), coded by the operon PputGB1_4083-4086, could produce the peptide backbone of PVD GB 1 . To verify this prediction, plasmid integration disruption of − PputGB1_4083 was performed and the resulting mutant failed to produce detectable PVD. In silico analysis of the modules in PputGB1_4083-4086 predicted a peptide sequence of Asp-Lys-Asp-Ser-Ala-Thr-Lsy-Orn, which closely matches the peptide determined by MS/MS. To extend these studies to other organisms, various Mn(II)-oxidizing and non-oxidizing isolates of P. putida, P. fluorescens, P. marincola, P. fluorescens-syringae group, P. mendocina-resinovorans group, and P. stutzerii group were screened for PVD synthesis. The PVD producers (12 out of 16 tested strains) were siderotyped and placed into four sets of differing PVD structures, some corresponding to previously characterized PVDs and some to novel PVDs. These results combined with previous studies suggested that the presence of OHAsp or the flexibility of the pyoverdine polypeptide may enable efficient binding of Mn(III).

Beyond iron: non-classical biological functions of bacterial siderophores

“…81 The most widely studied manganese-oxidizing bacteria are fluorescent pseudomonads. 87 The luminescence of these microbes results from production of pyoverdine siderophores. These siderophores impact manganese metabolism, forming Mn-pyoverdine complexes.…”

Chalkophores

“…Some metallophores also have secondary roles related to defense against metal toxicity. Although better known as siderophores, rhizoferrin and some desferrioxamines and pyoverdines have higher affinities for manganese than they do for iron (14–16). The broad-spectrum metallophore staphylopine binds both nickel and cobalt, and other compounds, including l -His 2 , l -His/2-methyl-2,4-thiazolidinedicarboxylic acid, and yet-uncharacterized metallophores, are implicated in nickel uptake as well (17–19).…”

Effects of exogenous pyoverdines on Fe availability and their impacts on Mn(II) oxidation by Pseudomonas putida GB-1

“…Out of these genes, PputGB1_4082 was located adjacent to the PVD synthase responsible for producing the peptide backbone of the PVD GB-1 (Parker et al, 2014). Since it was expected that PputGB1_4082 might therefore encode the ferri-PVD uptake receptor for PVD GB-1 , in-frame deletion of PputGB1_4082 was performed.…”

“…This mutant is deficient in PVD synthesis (Parker et al, 2014). The mutant was grown overnight in LB medium supplemented with 50 μgml −1 gentamicin.…”