Justine Marchand

Diatom Milking: A Review and New Approaches

The rise of human populations and the growth of cities contribute to the depletion of natural resources, increase their cost, and create potential climatic changes. To overcome difficulties in supplying populations and reducing the resource cost, a search for alternative pharmaceutical, nanotechnology, and energy sources has begun. Among the alternative sources, microalgae are the most promising because they use carbon dioxide (CO2) to produce biomass and/or valuable compounds. Once produced, the biomass is ordinarily harvested and processed (downstream program). Drying, grinding, and extraction steps are destructive to the microalgal biomass that then needs to be renewed. The extraction and purification processes generate organic wastes and require substantial energy inputs. Altogether, it is urgent to develop alternative downstream processes. Among the possibilities, milking invokes the concept that the extraction should not kill the algal cells. Therefore, it does not require growing the algae anew. In this review, we discuss research on milking of diatoms. The main themes are (a) development of alternative methods to extract and harvest high added value compounds; (b) design of photobioreactors; (c) biodiversity and (d) stress physiology, illustrated with original results dealing with oleaginous diatoms.

Impacts of mixtures of herbicides on molecular and physiological responses of the European flounder Platichthys flesus.

The widespread use of pesticides results in a growing contamination of the aquatic environment. The effects of (1) a simple mixture of a glyphosate-based formulation and AMPA (Aminomethylphosphonic acid--a primary metabolite of glyphosate) and of (2) a more complex mixture of herbicides (glyphosate/AMPA/mecoprop/acetochlor/2,4D) were explored on the molecular and physiological responses of the European flounder Platichthys flesus, considering a long-term and environmentally realistic contamination. Molecular responses were identified using suppression subtractive hybridization on liver samples: the level of gene transcription was significantly different between contaminated fishes vs control ones for 532 sequences, after a 62-day contamination. Among them, 222 sequences were identified by homology with data-based sequences; they encoded several metabolic pathways including: methionine and lipid metabolism, immunity, protein regulation, coagulation and energetic metabolism. Expression pattern of nine transcripts in the liver was confirmed by real-time PCR. The molecular study underlined that potential markers of liver injury were expressed for both mixtures, in particular betaine homocysteine methyl transferase and chemotaxin. Physiological responses were analysed considering blood parameters and condition factor; after the two months contamination period; no significant physiological difference was detected between contaminated and control fish.

Metallothionein genes from hydrothermal crabs (Bythograeidae, Decapoda): Characterization, sequence analysis, gene expression and comparison with coastal crabs

Hydrothermal vent conditions can alter DNA and hydrothermal organisms may develop detoxification mechanisms and/or genetic adaptations. Hydrothermal vent animals notably synthesize a high quantity of metallothioneins (MT). Recent studies have revealed that the levels of MT within hydrothermal crustacean tissues are higher than those found in other vent animals. To improve our understanding of the environmental impacts exerted on the vent organisms, we characterized the metallothioneins (cDNA and Mt genes) of several members of the Bythograeidae (Bythograea thermydron, Cyanagraea praedator and Segonzacia mesatlantica) which is the only endemic hydrothermal crab family. In comparison, the isolation of metallothionein cDNA was also carried out in several coastal crab families. The results showed that the hydrothermal crabs possess Mt composed of three exons and two introns presenting conserved splicing signals. The cDNA sequences isolated from distinct crabs showed multiple substitutions. In spite of the unique environmental conditions, the protein sequence analysis revealed no specific amino acid residue for the MT of the three hydrothermal crabs. However, gene expression analysis performed by real-time PCR based on S. mesatlantica (hydrothermal crab) compared to Pachygrapsus marmoratus (coastal crab) confirmed the higher metallothionein induction in hydrothermal crabs suggested by others authors.

Response of CO 2 -starved diatom Phaeodactylum tricornutum to light intensity transition

In this study, we investigated the responses of Phaeodactylum tricornutum cells acclimated to 300 µmol m−2 s−1 photon flux density to an increase (1000 µmol m−2 s−1) or decrease (30 µmol m−2 s−1) in photon flux densities. The light shift occurred abruptly after 5 days of growth and the acclimation to new conditions was followed during the next 6 days at the physiological and molecular levels. The molecular data reflect a rearrangement of carbon metabolism towards the production of phosphoenolpyruvic acid (PEP) and/or pyruvate. These intermediates were used differently by the cell as a function of the photon flux density: under low light, photosynthesis was depressed while respiration was increased. Under high light, lipids and proteins accumulated. Of great interest, under high light, the genes coding for the synthesis of aromatic amino acids and phenolic compounds were upregulated suggesting that the shikimate pathway was activated. This article is part of the themed issue ‘The peculiar carbon metabolism in diatoms’.

Carotenoids of Microalgae Used in Food Industry and Medicine.

BACKGROUND Since the industrial revolution, the consumption of processed food increased dramatically. During processing, food material loses many of its natural properties. OBJECTIVE The simple restoration of the original properties of the processed food as well as fortification require food supplementation with compounds prepared chemically or of natural origin. The observations that natural food additives are safer and better accepted by consumers than synthetic ones have strongly increased the demand for natural compounds. Because some of them have only a low abundance or are even rare, their market price can be very high. This is the case for most carotenoids of natural origin to which this review is dedicated. The increasing demand for food additives of natural origin contributes to an accelerated depletion of traditional natural resources already threatened by intensive agriculture and pollution. To overcome these difficulties and satisfy the demand, alternative sources for natural carotenoids have to be found. In this context, photosynthetic microalgae present a very high potential because they contain carotenoids and are able to produce particular carotenoids under stress. Their potential also resides in the fact that only ten thousands of microalgal strains have been described while hundred thousands of species are predicted to exist. Carotenoids have been known for ages for their antioxidant and coloring properties, and a large body of evidence has been accumulated about their health potential. CONCLUSION This review summarizes both the medicinal and food industry applications of microalgae with emphasis on the former. In addition, traditional and alternative microalgal sources used for industrial carotenoid extraction, the chemical and physical properties, the biosynthesis and the localization of carotenoids in algae are also briefly discussed.

Functional investigations in diatoms need more than a transcriptomic approach

The particular gene complement in diatoms, inherited from various types of organisms, has contributed to the development of metabolic networks that contrast with those found in other photosynthetic organisms. To understand these networks and how they are linked, transcriptomic, proteomic and metabolomic approaches have been used over the last decade. Understanding how these networks developed and interact remains a major goal for physiologists. Metabolic compartmentalization and fluxes between compartments are still poorly known, requiring: (1) the localization of proteins and biological activities, as well as potential protein isoforms and (2) relating metabolite measurements to pathway fluxes. Moreover, when considering metabolism, the identification of transcription factors, which are largely unknown for diatoms, is necessary. Integration of the results from these different approaches will complete our understanding of cell functioning and how differences impact metabolic reorientation.

An introduction to the vast world of transposable elements – what about the diatoms?

Transposable elements (TEs) are DNA sequences that are able to move and replicate within the genomes of virtually all organisms, ranging from animals to plants, and also including protozoans, bacteria and diatoms. Initially considered to be ‘junk DNA’ with no function, TEs are now thought to play a pivotal role in the evolution of genomes and organisms. This review is intended to provide non-specialists with an introduction to the world of TEs by summarizing the information available about these elements, ranging from their impact on genome structure to their potential involvement in the evolution of species. In this review, we propose to bring together what is known about the TEs and provide an overview of recent advances concerning TEs in diatoms.

Cadmium exposure exerts neurotoxic effects in peacock blennies Salaria pavo

Cadmium (Cd) is considered as an important factor involved in several neurological disturbances. The aim of this study was to assess the effects of Cd in the brain of peacock blennies Salaria pavo, a species used as a bioindicator of water pollution. A sublethal contamination of 2mg CdCl2 L-1 was performed over periods of 1, 4, 10 and 15 days. Total Cd accumulation was measured in brains and displayed low concentrations throughout the experiment. Partial-length cDNA of different ATP-binding cassette transporters (abcb1, abcc1, abcc2, abcg2 proteins) and acetylcholinesterase (ache) were characterized. mRNA expressions profiles displayed an up-regulation of abcc2 mRNA after 4 days of Cd exposure only while abcg2 mRNA was down-regulated after 10 days only. For AChE, the mRNA transcription and the activity of the enzyme were followed and highlighted that Cd exerted an inhibitory effect on the nervous information transmission. At the histological level, fish exhibited pathological symptoms in the optic tectum and the cerebellum and results showed that the cerebellum was the most affected organ.

Expression of the retrotransposons Surcouf and Blackbeard in the marine diatom Phaeodactylum tricornutum under thermal stress

Abstract: Transposable elements (TEs) are mobile DNA sequences thought to be involved in the genomic response to environmental stresses of organisms. The thermal stress behaviour of two retrotransposons (Surcouf and Blackbeard ) was investigated in the genome of two strains of the marine diatom Phaeodactylum tricornutum. Using quantitative reverse transcriptase polymerase chain reaction, the retrotransposon expression pattern was investigated after thermal stresses and compared with that of the small heat-shock protein (shsp). While the expression of Blackbeard was not affected by temperature changes, the retroelement Surcouf was markedly overexpressed in response to high temperature in correlation with shsp overexpression. An in silico analysis investigated the presence of regulatory heat-inducible motifs such as heat-shock elements, stress response elements and CCAAT boxes within the promoters of shsp and retrotransposons in the genome of P. tricornutum. The results of mRNA quantification are supported by the presence of heat-shock response motifs found in the promoters of shsp and the retrotransposon Surcouf.

Correction: Vinayak, V., et al. Diatom Milking: A Review and New Approaches. Marine Drugs 2015, 13, 2629–2665

The following two sentences, appearing on p 2642, need to be modified: “Using a new dedicated method, Daboussi et al. [232] targeted the diatom model organism Phaeodactylum tricornutum and used zinc finger nucleases, meganucleases, and transcription activator-like effector nucleases to edit Phaeodactylum tricornutum by inducing targeted mutagenesis of certain genes responsible for HVM production. This led to formation of a mutant diatom Tn 19745_1 that produces 45 times more lipid than the control and further increased the HVM production when grown in nutrient-stressed media.” These sentences should read (changes are indicated in bold) “Using a new dedicated method, Daboussi et al. [232] targeted the diatom model organism Phaeodactylum tricornutum and used zinc finger nucleases, meganucleases, and transcription activator-like effector nucleases TALEN to edit Phaeodactylum tricornutum by inducing targeted mutagenesis of certain genes responsible for HVM production. This led to formation of a mutant diatom Tn 19745_1 that produces 45 times more TAG than the control and further increased the HVM production when grown in nutrient-stressed media.” The authors would like to apologize for any inconvenience caused to the readers by these changes.