Extensive cross-disciplinary analysis of biological and chemical control of Calanus finmarchicus reproduction during an aldehyde forming diatom bloom in mesocosms

Egg and faecal pellet production and egg hatching success of the calanoid copepod Calanus finmarchicus were monitored over a period of 14 days (14-28 April, 2008) while fed water from 4 differently treated mesocosms and ambient water. Two of the mesocosms used were inoculated with the polyunsaturated aldehyde (PUA)-producing diatom Skeletonema marinoi, while 2 received only nutrient additions with or without silica. The mesocosms developed blooms of S. marinoi, mixed diatoms or the haptophyte Phaeocystis pouchetii, respectively. Faecal pellet production of C. finmarchicus increased with increasing food availability. Egg production increased with time in all mesocosms to a maximum single female production of 232 eggs female(-1) day(-1) (average of 90 eggs female(-1) day(-1)) and followed the development of ciliates and P. pouchetii, but was not affected by the observed high (up to 15 nmol L(-1)) PUA production potential of the phytoplankton. The hatching success of the eggs produced on the mesocosm diets was high (78-96%) and was not affected by either aldehydes in the maternal diet or exposure to the dissolved aldehydes in the water

Toxic Diatom Aldehydes Affect Defence Gene Networks in Sea Urchins.

Marine organisms possess a series of cellular strategies to counteract the negative effects of toxic compounds, including the massive reorganization of gene expression networks. Here we report the modulated dose-dependent response of activated genes by diatom polyunsaturated aldehydes (PUAs) in the sea urchin Paracentrotus lividus. PUAs are secondary metabolites deriving from the oxidation of fatty acids, inducing deleterious effects on the reproduction and development of planktonic and benthic organisms that feed on these unicellular algae and with anti-cancer activity. Our previous results showed that PUAs target several genes, implicated in different functional processes in this sea urchin. Using interactomic Ingenuity Pathway Analysis we now show that the genes targeted by PUAs are correlated with four HUB genes, NF-κB, p53, δ-2-catenin and HIF1A, which have not been previously reported for P. lividus. We propose a working model describing hypothetical pathways potentially involved in toxic aldehyde stress response in sea urchins. This represents the first report on gene networks affected by PUAs, opening new perspectives in understanding the cellular mechanisms underlying the response of benthic organisms to diatom exposure

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

© 2017, The Author(s).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 μM). 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

Growth phase-specific release of polyunsaturated aldehydes by the diatom Skeletonema marinoi

Polyunsaturated aldehydes (PUAs) have been extensively studied for their potential role in phytoplankton defence against grazers, but recently a potential infochemical role has been identified as well. We present here the first evidence of a synchronized release of PUAs from intact cells of a culture of the diatom Skeletonema marinoi. The release occurs transiently before the culture changes to the decline phase, providing a time-limited potential signal. When cultures are exposed during different stages of growth to PUAs in concentrations found in the medium, no general responses were found. However, a weak effect on cell concentration is observed exclusively when cultures in the late stationary phase are challenged with PUAs. Our results support for the first time the experimentally postulated hypothesis that PUA can play a role as infochemicals in mediating plankton interactions

Comparative metabolomics of the diatom Skeletonema marinoi in different growth phases

We introduce a rigorously validated protocol based on extraction, derivatisation and GC/MS for the analysis of diatom metabolomes. Using this methodology we characterised general patterns of the metabolism of the diatom Skeletonema marinoi during different growth phases. Canonical analysis of principal coordinate revealed clearly that the intracellular metabolites differ between exponential, stationary and declining phase. In addition, diurnal variation during the exponential phase was observed. A detailed analysis of the metabolic changes is presented and discussed in the context of previous physiological studies of diatoms. The observed variability in metabolites has a significant consequence for further physiological and ecological studies. Investigations have to take into account that diatom metabolism is a highly dynamic process and that food quality, chemical defence and also the production of signal molecules might be dependent on different growth phases or diurnal variations. The introduced protocol is in general suitable for the monitoring of microalgae and has also the potential to be applied to complex plankton communities

Metabolic profiling reveals growth stage variability in diatom exudates

We studied the patterns of waterborne metabolites released by diatom cultures during different growth phases. A carefully optimized enrichment procedure for metabolites from seawater medium facilitated the generation of large-scale sample sets that could be used for metabolic profiling. Samples from cartridge enrichments were directly submitted to ultraperformance liquid chromatography (UPLC) coupled with time-of-flight mass spectrometry (TOF-MS). Metabolic profiling revealed distinct patterns of metabolite release depending on the growth phases of the major bloom-forming diatoms Skeletonema marinoi and Thalassiosira pseudonana. Principal component analysis (PCA) enabled the recognition of specific metabolites that were only temporarily released by growing algal cultures. The exometabolome of the cells was complex and variable. The kinetics of metabolite release of some compounds resembles those of signal molecules involved in quorum sensing by bacteria. The introduced exometabolome investigation will help unravel the implications of release patterns of potential infochemicals for plankton ecology

Diatom exudates influence metabolism and cell growth of co-cultured diatom species

We surveyed the role of chemically mediated interactions between the 2 diatom species Skeletonema costatum and Thalassiosira weissflogii. S. costatum promoted the growth of T weissflogii in non-contact co-cultures, allowing an exchange of exuded metabolites. In contrast, cell counts of S. costatum were not affected by T weissflogii. Metabolic profiling of the co-culture medium revealed a significant change in diatom-derived metabolites in comparison with those of monoculture controls. Several compounds detected in monocultures were not present in the co-culturing set-up, indicating either a transformation or uptake of released metabolites by the competing species. In addition, metabolic profiling of intracellular metabolites revealed that the biochemical processes of both diatoms changed in the presence of the co-cultured species. The present study illustrates that chemical cross-talk between diatom species is possible and that these types of chemical interactions lead to physiological responses and might even result in changed cell abundances