The morphogenesis of the marine green algae Ulva mutabilis depends on bacteria that release diffusible morphogenetic compounds. Axenic U. mutabilis gametes develop into callus-like colonies without normal cell walls. From the accompanying microbial flora two specific bacteria were isolated, which form a symbiotic tripartite community and induce readily algal morphogenesis. We use axenic algal cultures as a powerful tool to investigate the multiple cross-kingdom interactions on a molecular level.

Metal isotope coded profiling (MICP) introduces a universal discovery platform for metal chelating natural products that act as metallophores, ion buffers or sequestering agents. The detection of cation and oxoanion complexing ligands is facilitated by the identification of unique isotopic signatures created by the application of isotopically pure metals.

•The production of polyunsaturated aldehydes (PUAs) by the green tide forming algae Ulva (Ria Formosa, Portugal) was surveyed.•Lipoxygenase mediated pathways catalyze the release of 2,4-decadienal and 2,4,7-decatrienal derived from PUFAs.•Only Ulva species with a blade-like morphotype produce PUAs indicating a chemotaxonomic relationship.•Pilot experiments were conducted to elucidate the biosynthetic pathways of PUA-production in Ulva.•The depletion of polyunsaturated fatty acids jeopardizes the amount of economical relevant resources from Ulva.Lipoxygenase/hydroperoxide lyase mediated transformations convert polyunsaturated fatty acids into various oxylipins. First, lipoxygenases catalyze fatty acid oxidation to fatty acid hydroperoxides. Subsequently, breakdown reactions result in a wide array of metabolites with multiple physiological and ecological functions. These fatty acid transformations are highly diverse in marine algae and play a crucial rule in e.g., signaling, chemical defense, and stress response often mediated through polyunsaturated aldehydes (PUAs). In this study, green tide-forming macroalgae of the genius Ulva (Chlorophyta) were collected at various sampling sites in the lagoon of the Ria Formosa (Portugal) and were surveyed for PUAs. We demonstrated that sea-lettuce like but not tube-like morphotypes produce elevated amounts of volatile C10-polyunsaturated aldehydes (2,4,7-decatrienal and 2,4-decadienal) upon tissue damage. Moreover, morphogenetic and phylogenetic analyses of the collected Ulva species revealed chemotaxonomic significance of the perspective biosynthetic pathways. The aldehydes are derived from omega-3 and omega-6 polyunsaturated fatty acids (PUFA) with 20 or 18 carbon atoms including eicosapentaenoic acid (C20:5 n-3), arachidonic acid (C20:4 n-6), stearidonic acid (C18:4 n-3), and γ-linolenic acid (C18:3 n-6). We present first evidences that lipoxygenase-mediated (11-LOX and 9-LOX) eicosanoid and octadecanoid pathways catalyze the transformation of C20- and C18-polyunsaturated fatty acids into PUAs and concomitantly into short chain hydroxylated fatty acids.

•Novel UHPLC-ToF-MS method for analysis of metallophores (metal-complexing ligands).•No sample preparation is required, and method validation shows satisfactory figures.•Quantification of cis-dioxido-Mo complexes and Fe-complexes with a single UHPLC run.•Application to the quantification of metallophores in aqueous bacterial samples.•Depletion rate of Mo-protochelin was compared with the bacterial uptake of Mo.Metallophores are a unique class of organic ligands released, for example, by nitrogen fixing bacteria in their environment in order to recruit the micronutrients molybdenum (Mo) and iron (Fe). Mo and Fe are essential cofactors of nitrogenase that reduces atmospheric nitrogen into bioavailable ammonium. Upon release, these bacterial metallophores bind to both metal cations and oxo-anions in the extracellular medium increasing the bioavailability of the metals to the nitrogen fixers, which can subsequently recruit the complexes. The efficient quantification of those metal complexes is crucial for the understanding of the homeostasis of the metal cofactors of nitrogenase (e.g., Fe and Mo), the dynamics of nitrogen fixation and the nitrogen cycle. A novel direct ultra-high-performance liquid chromatography coupled to a time-of-flight mass spectrometer (UHPLC-ToF-MS) was developed to quantify and monitor the production of Fe and Mo complexes of the catecholate metallophores protochelin (Prot) and azotochelin (Azo) in the growth medium of the nitrogen fixer and model organism Azotobacter vinelandii. Chromatographic separations were carried on a reversed C18-phase with a mobile phase ramped from water to acetonitrile spiked with 1 mmol/L ammonium acetate (pH 6.6) to achieve stability of the metal complexes. Linearity for Mo-protochelin and Fe-protochelin was found at the concentration range between 5.0 × 10−8 and 9.0 × 10−7 mol/L with a limit of detection of 2.0 × 10−8 and 3.0 × 10−8 mol/L, respectively. The coefficient of variation of the procedure is in the range from 1.5 to 3.4%. The validation has hence demonstrated that the UHPLC-ToF-MS methodology is a fast, precise, specific, robust, and sensitive approach allowing the direct measurement of metallophores in growth medium without any sample preparation. The UHPLC-ToF-MS methodology was applied to the analysis of metallophores in our laboratory. Under lower Mo concentration, the Mo-protochelin concentration peaks in the middle lag phase, while the Fe-protochelin concentration rises to two maxima at the beginning of the exponential phase and during the stationary phase. The results indicate that the production of metallophores is highly dynamic throughout the growth and has to be monitored with high sensitivity and temporal resolution.

Fixation of dinitrogen by soil bacteria is catalyzed by the enzyme nitrogenase which requires iron, molybdenum, and/or vanadium as metal cofactors. Under conditions of iron deficiency, the ubiquitous N2-fixing bacterium Azotobacter vinelandii produces azotobactin, a fluorescent pyoverdine-like compound which serves as a siderophore. Azotobatin’s hydroxamate, catechol, and α-hydroxy-acid moieties endow it with a very high affinity for FeIII, and the Fe complex is taken up by the bacterium. Here we show that azotobactin also serves for the uptake of Mo and V. Azotobactin forms strong complexes with molybdate and vanadate and the complexes are taken up by regulated transport systems. The kinetics of complexation of molybdate and vanadate by azotobactin are faster than the complexation of FeIII, which is either precipitated or bound to strong complexing agents. As a result of this kinetic advantage, the Mo and V complexes of azotobactin form despite the higher affinity of the compound for Fe, which is present in large excess in the environment. The results obtained here for azotobactin and previous data for the bis- and tris-catechols produced by A. vinelandii show that those “siderophores” are really “metallophores” that promote the bacterial acquisition of Mo and V in addition to Fe.