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9 Publications visible to you, out of a total of 9
Strategies and ecological roles of algicidal bacteria.

Abstract (Expand)

In both freshwater and marine ecosystems, phytoplankton are the most dominant primary producers, contributing substantially to aquatic food webs. Algicidal bacteria that can associate to microalgae … from the phytoplankton have the capability to control the proliferation and even to lyse them. These bacteria thus play an important role in shaping species composition in pelagic environments. In this review, we discuss and categorise strategies used by algicidal bacteria for the attack on microalgae. We highlight the complex regulation of algicidal activity and defence responses that govern alga-bacteria interactions. We also discuss how algicidal bacteria impact algal physiology and metabolism and survey the existing algicidal metabolites and enzymes. The review illustrates that the ecological role of algicidal bacteria is not yet fully understood and critically discusses the challenges in obtaining ecologically relevant data.

Authors: N. Meyer, A. Bigalke, A. Kaulfuss, G. Pohnert

Date Published: 30th Sep 2017

Publication Type: Not specified

Sticking together: inter-species aggregation of bacteria isolated from iron snow is controlled by chemical signaling

Abstract (Expand)

Marine and lake snow is a continuous shower of mixed organic and inorganic aggregates falling from the upper water where primary production is substantial. These pelagic aggregates provide a niche for … microbes that can exploit these physical structures and resources for growth, thus are local hot spots for microbial activity. However, processes underlying their formation remain unknown. Here, we investigated the role of chemical signaling between two co-occurring bacteria that each make up more than 10% of the community in iron-rich lakes aggregates (iron snow). The filamentous iron-oxidizing Acidithrix strain showed increased rates of Fe(II) oxidation when incubated with cell-free supernatant of the heterotrophic iron-reducing Acidiphilium strain. Amendment of Acidithrix supernatant to motile cells of Acidiphilium triggered formation of cell aggregates displaying similar morphology to those of iron snow. Comparative metabolomics enabled the identification of the aggregation-inducing signal, 2-phenethylamine, which also induced faster growth of Acidiphilium. We propose a model that shows rapid iron snow formation, and ultimately energy transfer from the photic zone to deeper water layers, is controlled via a chemically mediated interplay.

Authors: J. F. Mori, N. Ueberschaar, S. Lu, R. E. Cooper, G. Pohnert, K. Kusel

Date Published: 1st Feb 2017

Publication Type: Not specified

Symbiont-Derived Antimicrobials Contribute to the Control of the Lepidopteran Gut Microbiota

Abstract (Expand)

Insects develop efficient antimicrobial strategies to flourish in a bacterial world. It has long been proposed that native gut microbiota is an important component of host defense; however, the responsible … species have rarely been isolated to elucidate the mechanism of action. Here we show that the dominant symbiotic bacterium Enterococcus mundtii associated with the generalist herbivore Spodoptera littoralis actively secretes a stable class IIa bacteriocin (mundticin KS) against invading bacteria, but not against other gut residents, facilitating the normal development of host gut microbiota. A mundticin-defective strain lost inhibitory activity. Furthermore, purified mundticin cures infected larvae. Thus, the constitutively produced antimicrobials by native extracellular symbionts create a significant chemical barrier inside limiting invader expansion. This unique property also benefits E. mundtii itself by providing a competitive advantage, contributing to its dominance within complex microbial settings and its prevalence across Lepidoptera, and probably promotes the long-term cooperative symbiosis between both parties.

Authors: Y. Shao, B. Chen, C. Sun, K. Ishida, C. Hertweck, W. Boland

Date Published: 21st Jan 2017

Publication Type: Not specified

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

Searching for a Mate: Pheromone-Directed Movement of the Benthic Diatom Seminavis robusta

Abstract (Expand)

Diatoms are species-rich microalgae that often have a unique life cycle with vegetative cell size reduction followed by size restoration through sexual reproduction of two mating types (MT(+) and MT(-)). … In the marine benthic diatom Seminavis robusta, mate-finding is mediated by an L-proline-derived diketopiperazine, a pheromone produced by the attracting mating type (MT(-)). Here, we investigate the movement patterns of cells of the opposite mating type (MT(+)) exposed to a pheromone gradient, using video monitoring and statistical modeling. We report that cells of the migrating mating type (MT(+)) respond to pheromone gradients by simultaneous chemotaxis and chemokinesis. Changes in movement behavior enable MT(+) cells to locate the direction of the pheromone source and to maximize their encounter rate towards it.

Authors: K. G. Bondoc, C. Lembke, W. Vyverman,

Date Published: 5th Jun 2016

Publication Type: Not specified

Metabolic profiling identifies trehalose as an abundant and diurnally fluctuating metabolite in the microalga Ostreococcus tauri

Abstract (Expand)

INTRODUCTION: The picoeukaryotic alga Ostreococcus tauri (Chlorophyta) belongs to the widespread group of marine prasinophytes. Despite its ecological importance, little is known about the metabolism … of this alga. OBJECTIVES: In this work, changes in the metabolome were quantified when O. tauri was grown under alternating cycles of 12 h light and 12 h darkness. METHODS: Algal metabolism was analyzed by gas chromatography-mass spectrometry. Using fluorescence-activated cell sorting, the bacteria associated with O. tauri were depleted to below 0.1% of total cells at the time of metabolic profiling. RESULTS: Of 111 metabolites quantified over light-dark cycles, 20 (18%) showed clear diurnal variations. The strongest fluctuations were found for trehalose. With an intracellular concentration of 1.6 mM in the dark, this disaccharide was six times more abundant at night than during the day. This fluctuation pattern of trehalose may be a consequence of starch degradation or of the synchronized cell cycle. On the other hand, maltose (and also sucrose) was below the detection limit (~10 muM). Accumulation of glycine in the light is in agreement with the presence of a classical glycolate pathway of photorespiration. We also provide evidence for the presence of fatty acid methyl and ethyl esters in O. tauri. CONCLUSIONS: This study shows how the metabolism of O. tauri adapts to day and night and gives new insights into the configuration of the carbon metabolism. In addition, several less common metabolites were identified.

Authors: M. Hirth, S. Liverani, S. Mahlow, F. Y. Bouget, G. Pohnert, S. Sasso

Date Published: No date defined

Publication Type: Not specified

Photocontrolled Release of Chemicals from Nano- and Microparticle Containers.

Abstract (Expand)

A benzoin-derived diol linker was synthesized and used to generate biocompatible polyesters that can be fully decomposed on demand upon UV irradiation. Extensive structural optimization of the linker … unit was performed to enable the defined encapsulation of diverse organic compounds in the polymeric structures and allow for a well-controllable polymer cleavage process. Selective tracking of the release kinetics of encapsulated model compounds from the polymeric nano- and microparticle containers was performed by confocal laser scanning microscopy in a proof-of-principle study. The physicochemical properties of the incorporated and released model compounds ranged from fully hydrophilic to fully hydrophobic. The demonstrated biocompatibility of the utilized polyesters and degradation products enables their use in advanced applications, for example, for the smart packaging of UV-sensitive pharmaceuticals, nutritional components, or even in the area of spatially selective self-healing processes.

Authors: C. Englert, I. Nischang, C. Bader, P. Borchers, J. Alex, M. Prohl, M. Hentschel, M. Hartlieb, A. Traeger, G. Pohnert, S. Schubert, M. Gottschaldt, U. S. Schubert

Date Published: No date defined

Publication Type: Not specified

A giant type I polyketide synthase participates in zygospore maturation in Chlamydomonas reinhardtii.

Abstract (Expand)

Polyketide synthases (PKSs) occur in many bacteria, fungi and plants. They are highly versatile enzymes involved in the biosynthesis of a large variety of compounds including antimicrobial agents, … polymers associated with bacterial cell walls and plant pigments. While harmful algae are known to produce polyketide toxins, sequences of the genomes of non-toxic algae, including those of many green-algal species, have surprisingly revealed the presence of genes encoding type I PKSs. The genome of the model alga Chlamydomonas reinhardtii (Chlorophyta) contains a single type I PKS gene, designated PKS1 (Cre10.g449750), which encodes a giant PKS with a predicted mass of 2.3 MDa. Here, we show that PKS1 is induced in two-day old zygotes and is required for their development into zygospores, the dormant stage of the zygote. Wild-type zygospores contain knob-like structures (~50 nm diameter) that form at the cell surface and develop a central cell wall layer; both of these structures are absent from homozygous pks1 mutants. Additionally, in contrast to wild-type zygotes, chlorophyll degradation is delayed in homozygous pks1 mutant zygotes, indicating a disruption of zygospore development. In agreement with a role of the PKS in the formation of the highly resistant zygospore wall, mutant zygotes have lost the formidable desiccation tolerance of wild-type zygotes. Together, our results represent functional analyses of a PKS mutant in a photosynthetic eukaryotic microorganism, revealing a central function for polyketides in the sexual cycle and survival under stressful environmental conditions. This article is protected by copyright. All rights reserved.

Authors: N. Heimerl, E. Hommel, M. Westermann, D. Meichsner, M. Lohr, C. Hertweck, A. R. Grossman, M. Mittag, S. Sasso

Date Published: No date defined

Publication Type: Not specified

Algal Oxylipins Mediate the Resistance of Diatoms against Algicidal Bacteria.

Abstract (Expand)

Algicidal bacteria can lyse microalgal blooms and trigger shifts within plankton communities. Resistant algal species can escape lysis, and have the opportunity to dominate the phytoplankton after a … bacterial infection. Despite their important function in ecosystem regulation, little is known about mechanisms of resistance. Here, we show that the diatom Chaetoceros didymus releases eicosanoid oxylipins into the medium, and that the lytic algicidal bacterium, Kordia algicida, induces the production of several wound-activated oxylipins in this resistant diatom. Neither releases nor an induction occurs in the susceptible diatom Skeletonema costatum that is lysed by the bacterium within a few days. Among the upregulated oxylipins, hydroxylated eicosapentaenoic acids (HEPEs) dominate. However, also, resolvins, known lipid mediators in mammals, increase upon exposure of the algae to the algicidal bacteria. The prevailing hydroxylated fatty acid, 15-HEPE, significantly inhibits growth of K. algicida at a concentration of approximately 1 microM. The oxylipin production may represent an independent line of defense of the resistant alga, acting in addition to the previously reported upregulation of proteases.

Authors: N. Meyer, J. Rettner, M. Werner, O. Werz, G. Pohnert

Date Published: No date defined

Publication Type: Not specified

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