Polyphenolic compounds on leaves limit iron availability and affect growth of epiphytic bacteria

Polyphenolic compounds produced by plants can chelate iron, reducing its bioavailability to plant‐associated bacteria. In response to limited iron levels, most bacteria produce siderophores to acquire needed iron quantities. The amount of phenolic compounds detected in methanolic washings of leaves of different plant species varied greatly, being nearly sevenfold higher in Viburnum tinus than in Phaseolus vulgaris. In species with high levels of total phenolics (e.g. Pelargonium hortorum), tannin concentration of leaf washings was also high and accounted for up to 85% of total phenolics. Both stimulation of production of the siderophore pyoverdine in Pseudomonas syringae strain B728a and inhibition of growth of an isogenic mutant I‐1, deficient in pyoverdine production were associated with plants harbouring high levels of leaf surface phenolics. Levels of tannic acid sufficient to inhibit growth of the pyoverdine mutant in culture in an iron‐reversible fashion were similar to tannin levels found on leaves of plants such as P. hortorum. Additionally, the amount of pyoverdines produced by P. syringae and quantified in leaf washings from a variety of plants was directly related to the concentration of tannins released from the leaf, indicating that tannins were responsible for sequestering iron. Phenolic compounds, principally tannins, may thus play an important role in plant–microbe interactions.     

Investigation of intermittent air exposure on four-stage and one-stage anaerobic semi-continuous mixed-acid fermentations

This study evaluated anaerobic mixed-acid countercurrent fermentations in both strict S (minimal oxygen) and relaxed R (high oxygen) conditions. In relaxed fermentations, filter solids and liquids were exposed to air for 90 min every 56 h. The total acid concentrations for four-stage trains were 23.0 (4S) and 22.1 (4R) g/L_Liq, and for one-stage trains were 17.2 (1S) and 18.4 (1R) g/L_Liq. The strict and relaxed trains had statistically similar exit yields. The strict trains had significantly more high-molecular-weight carboxylic acids. The relaxed trains had slightly higher conversion and slightly lower selectivity, but not significantly. Air exposure had no significant effect on the bacterial profiles of the strict and relaxed fermentations. For all fermentations, the most abundant bacterial genus was Prevotella, a strict anaerobe. This study shows that the mixed-culture community is oxygen tolerant because it maintains fermentation performance during oxygen-induced stress.     

Synthesis and characterization of binuclear rhenium(I) complexes containing bifunctional ligands

The ligand exchange reaction of the anionic binuclear rhenium complexes (R = H (1), or Me (2)) has been studied with the bifunctional ligands 2-aminophenol (3), 4-hydroxypyridine (4), 3-hydroxybenzoic acid (5), and 3-pyridylcarbinol (6). The reactivity the pendant pyridyl group of 6 was studied in reactions with the Lewis acids ZnCl₂ (7), and AgPF₆ (8). Crystal structure determinations for several of these derivatives have been carried out which reveal both discrete and polymeric complexes upon addition of the Lewis base.     

Photoluminescent metal-organic framework with hex topology constructed from infinite rod-shaped secondary building units and single e,e-trans-1,4-cyclohexanedicarboxylic dianion

Hydrothermal reaction produced a three-dimensional zinc 1,4-cyclohexanedicarboxylate formulated as Zn₅(μ³-OH)₂(trans-chdc)₄ (chdc = 1,4-cyclohexanedicarboxylic dianion) in high purity and good yield, which is constructed from infinite rod-shaped Zn-O-C secondary building units interconnected by -C₆H₁₂-cyclohexane rings of the ligands. The topology of the framework can be regarded as hex type. Though it is synthesized from 1,4-cyclohexanedicarboxylic acid with mixed conformations (trans and cis), interestingly, the ligands in the compound Zn₅(μ³-OH)₂(trans-chdc)₄ are uniformly in e,e-trans conformation. This may be related to its synthetic conditions. Photoluminescence measurement reveals that the compound exhibits intense violet-blue fluorescent emission at room temperature. Origin of the emission can be assigned to intraligand transitions by comparison of the fluorescent emission bands for the free ligand chdcH₂ and the compound Zn₅(μ³-OH)₂(trans-chdc)₄.     

Synthesis and solution behavior of the trinuclear palladium(II) unsaturated carboxylate complexes triangle-Pd3[μ-O2CC(R′) = CHMe]6 (R′ = Me, H): X-ray structure of palladium(II) tiglate (R′ = Me)

The first examples of binary palladium(II) derivatives of unsaturated carboxylic acids are reported. It was found that the interaction of Pd₃(μ-OAc)₆ with the ,β-unsaturated 1-methylcrotonic (tiglic) and crotonic acids leads to the corresponding carboxylates of composition Pd₃[μ-O₂CC(R′) = CHMe]₆, where R′ = Me (1) or H (2). The new compounds have been characterized by elemental analysis, solid and solution IR, ¹H and ¹³C NMR, and ESI mass spectrometry. The crystal structure of 1 has been determined. This molecule displays a central Pd₃ cyclic core with Pd–Pd distances of 3.093–3.171 Å. Each Pd–Pd bond is bridged by a pair of carboxylate ligands, one above and the other below the Pd₃ plane, providing a square planar coordination for each Pd atom in an approximate D_3h overall symmetry arrangement. Solution spectroscopic data show that the bridging η¹:η¹:μ₂ interaction of the carboxylates of 1 and 2 is readily displaced, with a change of the ligand to the terminal (η¹) coordination mode.     

Phaeobacter gallaeciensis genomes from globally opposite locations reveal high similarity of adaptation to surface life

Phaeobacter gallaeciensis, a member of the abundant marine Roseobacter clade, is known to be an effective colonizer of biotic and abiotic marine surfaces. Production of the antibiotic tropodithietic acid (TDA) makes P. gallaeciensis a strong antagonist of many bacteria, including fish and mollusc pathogens. In addition to TDA, several other secondary metabolites are produced, allowing the mutualistic bacterium to also act as an opportunistic pathogen. Here we provide the manually annotated genome sequences of the P. gallaeciensis strains DSM 17395 and 2.10, isolated at the Atlantic coast of north western Spain and near Sydney, Australia, respectively. Despite their isolation sites from the two different hemispheres, the genome comparison demonstrated a surprisingly high level of synteny (only 3% nucleotide dissimilarity and 88% and 93% shared genes). Minor differences in the genomes result from horizontal gene transfer and phage infection. Comparison of the P. gallaeciensis genomes with those of other roseobacters revealed unique genomic traits, including the production of iron-scavenging siderophores. Experiments supported the predicted capacity of both strains to grow on various algal osmolytes. Transposon mutagenesis was used to expand the current knowledge on the TDA biosynthesis pathway in strain DSM 17395. This first comparative genomic analysis of finished genomes of two closely related strains belonging to one species of the Roseobacter clade revealed features that provide competitive advantages and facilitate surface attachment and interaction with eukaryotic hosts.     

Synthesis, crystal structure and luminescence properties of two novel lanthanide coordination polymers containing double chain

Two novel lanthanide(III) two-dimensional (2D) coordination polymers [Ln₂(PDC)₂(OH)₂(H₂O)₂] · H₂O (Ln = Eu (1) and Tb (2), H₂PDC = pyridine-3,4-dicarboxylic acid) have been prepared under hydrothermal conditions and characterized by elemental analysis, IR, TGA and single-crystal X-ray diffraction. Compounds 1 and 2 crystallize in the triclinic system, space group , they are isostructural and exhibit the same two-dimensional topological network constructed by PDC-connected Ln-O-Ln double chains. Photoluminescence properties of the compounds 1 and 2 have been investigated in the solid state at room temperature.     

Mono- and bimetallic gold(I) and silver(I) pentafluoropropionates and related compounds

A series of eight new carboxylate complexes of the general type (L)_nMOC(O)R (L=PMe₃; n=1; M=Ag, Au; R=C₂F₅. L=PPh₃; n=1-3; M=Ag; R=C₂F₅, t-Bu) have been prepared in high yields. Crystal and molecular structures have been determined for three representative examples. The crystal structure of (Ph₃P)AgOC(O)C₂F₅ contains dimers in which the silver atoms are bridged by the carboxylate oxygen atoms. This bridging resembles the structural motif found in silver carboxylates without ligand support. Usage of the smaller phosphine PMe₃ leads to the formation of a polymeric chain structure in (Me₃P)AgOC(O)C₂F₅ with bridging carboxylate anions and short Ag-Ag contacts holding the monomers together. The reaction of (4-Me₂N-C₆H₄)Ph₂ PAuCl with two equivalents of C₂F₅CO₂Ag leads to the formation of a mixed metal product containing both gold and silver. The crystal structure analysis of this compound revealed a tetranuclear complex containing a central dimeric silver pentafluoropropionate unit which is chelated by the (triarylphosphine)gold(I) pentafluoropropionate molecules via Ag-Au metallophilic contacts and Ag-O donor/acceptor interactions.     

Pseudomonas mosselii E1铁载体合成相关基因cysI的克隆与功能初步分析

从棉花根际分离的铁载体产生菌E1,其16SrDNA与Pseudomonas mosselii ATCCBAA-99的同源性为100%。采用三亲本杂交方法将携带转座子Tn5-1063的质粒pRL1063a导入E1中进行转座子插入诱变。利用CAS法,从1000个突变株中,筛选到一株铁载体合成缺失突变株E1-185。利用TAIL-PCR方法,扩增位于Tn5-1063两端的侧翼序列。测序结果表明,转座子插入到E1的cysI基因内。该基因与Pseudomonas entomophila L48的cysI同源性为96%,其CysI氨基酸序列相似性为97%。该基因与半胱氨酸的合成密切相关,而在加有半胱氨酸的CAS平板上,突变株恢复了铁载体产生能力,证明cysI在E1铁载体合成过程中具有重要作用。据推测,cysI可能与铁载体合成途径中关键蛋白acyl-S-PCPs的形成有关。