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Published year: 20164
A fast and direct liquid chromatography-mass spectrometry method to detect and quantify polyunsaturated aldehydes and polar oxylipins in diatoms

Abstract (Expand)

Polyunsaturated aldehydes (PUAs) are a group of microalgal metabolites that have attracted a lot of attention due to their biological activity. Determination of PUAs has become an important routine … procedure in plankton and biofilm investigations, especially those that deal with chemically mediated interactions. Here we introduce a fast and direct derivatization free method that allows quantifying PUAs in the nanomolar range, sufficient to undertake the analysis from cultures and field samples. The sample preparation requires one simple filtration step and the initiation of PUA formation by cell disruption. After centrifugation the samples are ready for measurement without any further handling. Within one chromatographic run this method additionally allows us to monitor the formation of the polar oxylipins arising from the cleavage of precursor fatty acids. The robust method is based on analyte separation and detection using ultra high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (UHPLC-APCI MS) and enables high throughput investigations by employing an analysis time of only 5 min. Our protocol thus provides an alternative and extension to existing PUA determinations based on gas chromatography-mass spectrometry (GC-MS) with shorter run times and without any chemical derivatization. It also enables researchers with widely available LC-MS analytical platforms to monitor PUAs. Additionally, non-volatile oxylipins such as ω-oxo-acids and related compounds can be elucidated and monitored.

Authors: Constanze Kuhlisch, Michael Deicke, Nico Ueberschaar, Thomas Wichard, Georg Pohnert

Date Published: 15th Oct 2016

Publication Type: Not specified

Bakterien-induzierte Morphogenese der marinen Makroalge Ulva

Abstract (Expand)

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.

Author: Thomas Wichard

Date Published: 2nd Oct 2016

Publication Type: Not specified

Identification of Metallophores and Organic Ligands in the Chemosphere of the Marine Macroalga Ulva (Chlorophyta) and at Land-Sea Interfaces

Abstract (Expand)

The roles of organic matter in seawater have often been discussed from the aspect of metal toxicity and bioavailability in seawater. In fact, organic ligands, as part of the organic matter, can work … as a trace metal ion buffer system. At the same time, however, the release of well-defined metal chelators as exudates by, for example, marine bacteria is necessary to compete with natural metal complexes and sustain the metal acquisition required for several processes including nitrogen fixation. The identification, isolation, and structure elucidation of chelators is, thus, essential to our understanding of metal stress management in the natural habitat and role of these chelators on cellular process. The isolation of an organic ligand from its chemosphere is a challenging task. The purpose of this paper is, therefore, to give an additional perspective on how the effective application of stable isotope pairs of a metal of interest (both cations and oxoanions) combined with mass spectrometric analyses can pave the way to discovering new organic ligands (i.e., metallophores) and the chelating characteristics of dissolved organic matter (DOM): Pairs of isotopes, such as 54Fe and 58Fe (or any other pair of available isotopes of a given metal), can be used to create easily detectable unique isotopic signatures in mass spectra when they are bound by chelators. The identification of organic ligands is outlined for a proposed model system of mutualistic interactions between the green macroalga Ulva (Chlorophyta) and associated bacteria, as well as discussed briefly for DOM along land-sea gradients. Overall, the characterization of a broader spectrum of chelators in aquatic systems will open a new window to decipher the eco-physiological functions of organic ligands as a metal ion buffer and metallophores in metal cycling in marine ecosystems.

Author: Thomas Wichard

Date Published: 29th Jul 2016

Publication Type: Not specified

Macroalgal Morphogenesis Induced by Waterborne Compounds and Bacteria in Coastal Seawater

Abstract (Expand)

Axenic gametes of the marine green macroalga Ulva mutabilis Foyn (Ria Formosa, locus typicus) exhibit abnormal development into slow-growing callus-like colonies with aberrant cell walls. Under laboratory … conditions, it was previously demonstrated that all defects in growth and thallus development can be completely abolished when axenic gametes are inoculated with a combination of two specific bacterial strains originally identified as Roseobacter sp. strain MS2 and Cytophaga sp. strain MS6. These bacteria release diffusible morphogenetic compounds (= morphogens), which act similar to cytokinin and auxin. To investigate the ecological relevance of the waterborne bacterial morphogens, seawater samples were collected in the Ria Formosa lagoon (Algarve, Southern Portugal) at 20 sampling sites and tidal pools to assess their morphogenetic effects on the axenic gametes of U. mutabilis. Specifically the survey revealed that sterile-filtered seawater samples can completely recover growth and morphogenesis of U. mutabilis under axenic conditions. Morphogenetic activities of free-living and epiphytic bacteria isolated from the locally very abundant Ulva species (i.e., U. rigida) were screened using a multiwell-based testing system. The most represented genera isolated from U. rigida were Alteromonas, Pseudoalteromonas and Sulfitobacter followed by Psychrobacter and Polaribacter. Several naturally occurring bacterial species could emulate MS2 activity (= induction of cell divisions) regardless of taxonomic affiliation, whereas the MS6 activity (= induction of cell differentiation and cell wall formation) was species-specific and is probably a feature of difficult-to-culture bacteria. Interestingly, isolated bacteroidetes such as Algoriphagus sp. and Polaribacter sp. could individually trigger complete Ulva morphogenesis and thus provide a novel mode of action for bacterial-induced algal development. This study also highlights that the accumulation of algal growth factors in a shallow water body separated from the open ocean by barrier islands might have strong implications to, for example, the wide usage of natural coastal seawater in algal (land based) aquacultures of Ulva.

Authors: J. Grueneberg, A. H. Engelen, R. Costa,

Date Published: 8th Jan 2016

Publication Type: Not specified

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