Cluster-root formation, carboxylate exudation and proton release of Lupinus pilosus Murr. as affected by medium pH and P deficiency

The study examined the interactive effect of pH and P supply on cluster-root formation, carboxylate exudation and proton release by an alkaline-tolerant lupin species (Lupinus pilosus Murr.) in nutrient solution. The plants were exposed to 1 (P₁, deficient) and 50 μM P (P₅₀, adequate) for 34 days in nutrient solution at either pH 5.6 or 7.8. Plant biomass was not influenced by pH at P₁, but at P₅₀ shoot and root dry weights were 23 and 18% higher, respectively, at pH 7.8 than at pH 5.6. There was no significant difference in plant biomass between two P treatments regardless of medium pH. Phosphorus deficiency increased significantly the number of the second-order lateral roots compared with the P₅₀ treatment. Both total root length and specific root length of plants grown at pH 5.6 were higher than those at pH 7.8 regardless of P supply. Cluster roots were formed at P₁, but cluster-root number was 2-fold higher at pH 7.8 than pH 5.6. Roots released 16 and 31% more protons at pH 5.6 and 7.8, respectively, in P₁ than in P₅₀ treatments, and the rate of proton release followed the similar pattern. At pH 5.6, citrate exudation rate was 0.39 μmol g⁻¹ root DW h⁻¹ at P₁, but was under the detection limit at P₅₀; at pH 7.8, it was 2.4-fold higher in P₁ than in P₅₀ plants. High pH significantly increased citrate exudation rate in comparison to pH 5.6. The uptake of anions P and S was inhibited at P₁ and high pH increased cations Na, Mg and Ca uptake. The results suggested that enhanced cluster-root formation, proton release and citrate exudation may account for the mechanism of efficient P acquisition by alkaline-tolerant L. pilosus well adapted to calcareous soils. Cluster-root formation and citrate exudation in L. pilosus can be altered by medium pH and P deficiency. Phosphorus deficiency-induced proton release may be associated with the reduced anion uptake, but high pH-induced proton release may be partly attributed to increased cation uptake.     

Synthesis, structures and thermal properties of three new two-dimensional coordination networks assembled by lanthanide salts and carboxylate ligand

Three new rare-earth coordination polymers, [La₂(PDC)₂(NO₃)₂(H₂O)₃] (1) and [Dy(PDC)(ox)_0.5(H₂O)₂] · H₂O (2), and [Sm(PDC)(ox)_0.5(H₂O)₂] · H₂O (3) (H₂PDC = pyridine-3,4-dicarboxylic acid, ox = oxalic acid), have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, TGA, and single-crystal X-ray diffraction. Of the three compounds, La-O-La and Dy(Sm)-O-C-O-Dy(Sm) chains are cross-linked by PDC ligands into interesting two-dimensional framework structures. They represent, to the best of our knowledge, the first examples of rare-earth complexes in the {M/PDC} (M = metal) system.     

Cost of cooperation rules selection for cheats in bacterial metapopulations

Bacteria secrete a large variety of beneficial metabolites into the environment, which can be shared as public goods among producing bacteria, but also be exploited by nonproducing cheats. Here, we focus on cooperative production of iron-chelating molecules (siderophores) in the bacterium Pseudomonas aeruginosa to study how relevant ecological factors influence selection for cheating. We designed patch-structured metapopulations that allowed us introducing among-patch ecological variation. We found that cheating readily evolved in uniform iron-limited environments. This finding is explained by severe iron limitation demanding high siderophore-production efforts, which results in high metabolic costs accruing to cooperators, and thereby facilitates the spread of cheats. In contrast, we observed a significant reduction or even negation of selection for cheating in metapopulations where we introduced patches with increased iron availability and/or opportunities to recycle siderophores. These findings are compatible with the view that cheats are less likely to invade in environments that allow bacteria to reduce siderophore-production efforts, as this lowers the overall metabolic costs accruing to cooperators. Because we increased iron availability and siderophore recycling opportunities moderately, and only in some patches, our findings demonstrate that already-small local variations in ecological conditions as occurring in nature can significantly affect selection for public-goods secretion in microbes. In addition, we found that most (84.6%) of the evolved cheats were partially deficient for siderophore production and not loss-of-function mutants. Genetic considerations indicate that mutations leading to partial deficiency occur more frequent than mutations leading to loss of function, but also suggest that partially deficient mutants might often be the more competitive cheats.     

Complexation of 2-hydroxynicotinic and 3-hydroxypicolinic acids with zinc(II). Solution state study and crystal structure of trans-diaqua-bis-(3-hydroxypicolinato)zinc(II)

The interactions between zinc(II) and the two ligands 2-hydroxynicotinic acid (HNic) and 3-hydroxypicolinic acid (HPic) have been investigated by means of potentiometric titrations in aqueous 0.6 m (Na)Cl at 25 °C. In both cases, only mononuclear complexes are formed. The qualitative and quantitative results obtained have been confirmed in part by UV-Vis spectrophotometry and ¹H NMR spectroscopy. The complex trans-diaqua-bis-(3-hydroxypicolinato)zinc(II) was obtained as a crystal and examined by X-ray crystallography. The thermodynamic results allow drawing some conclusions regarding the extent of Zn(II) interference in a hypothetical chelation therapy treatment of aluminium or iron overload with these two ligands.     

Heterobactins: A new class of siderophores from Rhodococcus erythropolis IGTS8 containing both hydroxamate and catecholate donor groups

We report here on a new class of siderophores isolated from Rhodococcus erythropolis IGTS8, the first structurally characterized from any species of Rhodococcus and for which we suggest the name heterobactins. These siderophores consist of a tripeptide of sequence (N-OH)-L-Orn-Gly-D-Orn-(delta-N-dihydroyxbenzoate). The alpha amino group of the D-Orn is derivatized either as a 2-hydroxybenzoxazolate in heterobactin A or remains free in heterobactin B. The structures were determined by a combination of amino acid analysis, mass spectrometry and NMR methods. The two new compounds are true siderophores in that they relieve iron limited growth in the producing strain. The heterobactins are also transported by other non-producing bacteria. Growth promotion tests using various transport mutants revealed that in E. coli heterobactin A is only recognized by the catecholate receptor Cir while heterobactin B is taken up in both E.coli and A. flavescens JG9 via a hydroxamate transport system.     

The remarkable hydrophobic effect of a fatty acid side chain on the microbial growth promoting activity of a synthetic siderophore

The ability of synthetic derivatives of the siderophore tripeptide of N ⁵-hydroxy-N ⁵-acetyl-l-ornithine to promote the growth of various strains of mycobacteria and Gram negative bacteria was found to depend significantly on the hydrophobic nature of the derivative. Although the tripeptide of N ⁵-hydroxy-N ⁵-acetyl-l-ornithine is not normally utilized by mycobacteria, an N-terminal palmitoyl derivative mimicked natural mycobactin J in all studies.     

Synthetic siderophores as biological probes

Summary Synthetic molecules that mimic the properties of the natural siderophores promise to become powerful tools in the exploration of microbial iron(III)-uptake phenomena. Such molecules can serve as probes to (i) establish the essential structural requirements for biological action, (ii) trace alternative reaction pathways and (iii) compare receptors of different biological origins. In this article a series of synthetic ferrichrome analogs will be described. The strategy adopted for the design and synthesis of these compounds will be outlined and their properties in vitro and in vivo examined. The growth promotion activity of these compounds inArthrobacter flavescens is used to map the ferrichrome receptor surface. Their activities towardsZea mays allow us to trace the plants' reductive iron(III) uptake routes. Potential applications of modified ferrichrome analogs for the isolation of ferrichrome receptors, the generation of fluorescent probes and ultimately new families of antibiotic or antifungal agents, will also be indicated.     

Characterization of the chromophores of pyoverdins and related siderophores by electrospray tandem mass spectrometry

Characteristic fragment ions of the various chromophores of the pyoverdin siderophore family obtained by collision activated dissociation of the [M+2H]²⁺ ions are reported allowing unambiguous identification. Tandem mass spectrometrical studies revealed the existence of the first example of a ferribactin with a succinamide side chain, and they add some information to the problem in which way a malic acid side chain is attached to the chromophore.     

Numerical taxonomy of fluorescent Pseudomonas associated with tomato roots

The phenetic taxonomy of 110 fluorescent bacterial strains, isolated from the roots of tomatoes and other plants was numerically studied through 97 features including 69 assimilation tests. Thirty-two reference strains of various Pseudomonas spp. were additionally included. The strains clustered into 16 clusters at the 74% similarity level when using Jaccard similarity coefficients. Almost all field strains belonged to the P. fluorescens/P. putida-complex while none clustered with P. syringae and allied bacteria. The biovar II branch, as well as the newly described biovar VI of P. fluorescens, made up 55% and 20% respectively, of the field strains; two % were allocated to P. fluorescens biovar I and three % to biovar IV. Eleven % of the root associated strains were designated P. putida; six strains were biovar A, three strains biovar B while four strains could not be referred to any known biovar. The continuum within the P. fluorescens/P. putida-complex as well as the taxonomic status of the six biovars of P. fluorescens and the three biovars of P. putida are discussed.     

Degradation of desferrioxamines by Azospirillum irakense: Assignment of metabolites by HPLC/electrospray mass spectrometry

Based on a recent finding that an Azospirillum isolate ASP-1 possessing high 16S rDNA similarity to Azospirillum irakense was able to degrade desferrioxamine type siderophores (Winkelmann et al. BioMetals 9, 78-83, 1996), various members of the genus Azospirillum were analyzed for their ability to degrade desferrioxamines. While the desferrioxamine-degrading activity was absent or scarcely detectable in strains of A. lipoferum, A. brasilense, A. amazonense, degradation activity seemed to be confined to the species A. irakense (KBC-1, KA3). Also the identity of strain ASP-1 as A. irakense could be confirmed by species-specific oligonucleotide hybridization, InterLINE PCR fingerprinting and carbon source utilization pattern (BIOLOG) analysis. Products of desferrioxamine B degradation were analyzed by analytical HPLC and HPLC/electrospray mass spectrometry. Using whole cells and purified enzyme it was shown that the trihydroxamate desferrioxamine B (561 amu) is split at the N-terminal amide bond yielding a monohydroxamate (MH₁, 219 amu) and a dihydroxamate (DH₁, 361 amu) metabolite. A second monohydroxamate (MH₂, 319 amu) resulted from DH₁ after splitting the acetylhydroxamate bond. Minor amounts of a further dihydroxamate (DH₂, 419 amu) originated from splitting the second amide bond in desferrioxamine B. In addition to desferrioxamine B, several other linear and cyclic desferrioxamines and derivatives were degraded, whereas desferricoprogen and desferri-ferrichrome were not degraded, indicating high substrate specificity of the desferrioxamine hydrolase in A. irakense species. A simple microtiter plate assay was developed which can be used to phenotypically discriminate and identify species of A. irakense from other Azospirillum species by their characteristic feature of desferrioxamine degradation.