Digital expression profiling of novel diatom transcripts provides insight into their biological functions

Background: Diatoms represent the predominant group of eukaryotic phytoplankton in the oceans and are responsible for around 20% of global photosynthesis. Two whole genome sequences are now available. Notwithstanding, our knowledge of diatom biology remains limited because only around half of their genes can be ascribed a function based onhomology-based methods. High throughput tools are needed, therefore, to associate functions with diatom-specific genes. Results: We have performed a systematic analysis of 130,000 ESTs derived from Phaeodactylum tricornutum cells grown in 16 different conditions. These include different sources of nitrogen, different concentrations of carbon dioxide, silicate and iron, and abiotic stresses such as low temperature and low salinity. Based on unbiased statistical methods, we have catalogued transcripts with similar expression profiles and identified transcripts differentially expressed in response to specific treatments. Functional annotation of these transcripts provides insights into expression patterns of genes involved in various metabolic and regulatory pathways and into the roles of novel genes with unknown functions. Specific growth conditions could be associated with enhanced gene diversity, known gene product functions, and over-representation of novel transcripts. Comparative analysis of data from the other sequenced diatom, Thalassiosira pseudonana, helped identify several unique diatom genes that are specifically regulated under particular conditions, thus facilitating studies of gene function, genome annotation and the molecular basis of species diversity. Conclusions: The digital gene expression database represents a new resource for identifying candidate diatom-specific genes involved in processes of major ecological relevance

New insights into the role of motion and form vision in neurodevelopmental disorders

A selective deficit in processing the global (overall) motion, but not form, of spatially extensive objects in the visual scene is frequently associated with several neurodevelopmental disorders, including preterm birth. Existing theories that proposed to explain the origin of this visual impairment are, however, challenged by recent research. In this review, we explore alternative hypotheses for why deficits in the processing of global motion, relative to global form, might arise. We describe recent evidence that has utilised novel tasks of global motion and global form to elucidate the underlying nature of the visual deficit reported in different neurodevelopmental disorders. We also examine the role of IQ and how the sex of an individual can influence performance on these tasks, as these are factors that are associated with performance on global motion tasks, but have not been systematically controlled for in previous studies exploring visual processing in clinical populations. Finally, we suggest that a new theoretical framework is needed for visual processing in neurodevelopmental disorders and present recommendations for future research

L'échouement de l'Amoco Cadiz : conséquences sur les peuplements algaux des côtes bretonnes

Les 300 km du littoral breton touchés par les hydrocarbures de l'Amoco Cadiz sont parmi les plus productifs quant à l'exploitation des algues. L'ISTPM a suivi l'évolution des peuplements de Laminaria digitata et de Chondrus crispus, algues les plus utilisées par les industries locale et fait état des perturbations physiologiques engendrées par la pollution par les hydrocarbures

Cryopreservation of gametophytes of Laminaria digitata (L) lamouroux by encapsulation dehydration

A cryopreservation procedure was developed for gametophytes of Laminaria digitata using an encapsulation-dehydration technique. Cells were encapsulated in calcium alginate beads pretreated for 6 h in liquid medium containing 0.3 to 0.5 M sucrose and then dehydrated. Freezing was performed in two steps, the first consisting of a slow temperature decrease from 19°C to -40°C and the second of direct immersion of samples in liquid nitrogen. Thawing was performed in a water bath at 40°C for 2 min. Survival rates were between 25 and 75% depending on age, sex and stress. The best results were obtained with alginate beads pretreated for 6 h in a 0.3-0.4 M sucrose solution and dehydrated down to 40% of the initial wet weight. Recovery time was about two weeks

Transient initial phase in continuous culture of

Starting microalgae continuous culture generally includes a preliminary batch culture to obtain sufficient cell density. It is possible to apply continuous regime from the beginning of the culture (IC mode) rather than to begin by an initial batch (IB mode). It is our purpose to check that both initial modes lead to identical steady-state cell characteristics. The microalga Isochrysis galbana affinis Tahiti was used for this comparative study. With an initial cell density of 5 × 105 cell ml–1 and a dilution rate of about 1.0 d–1, both IB and IC modes led to identical cell density once steady-state is reached between 6 and 8 d after inoculation in the two cases. Cell concentration of chlorophyll a and pheopigment a were found to be similar for IB and IC modes at steady-state. Initial culture conditions did not influence saturation irradiance and oxygen consumption rate, which were found to be 650 ± 143 μmol phot m–2 s–1 and 1.54 × 10–3 ± 10–5 μmol O2 ml–1 min–1, respectively. At steady-state, nutrient cell uptakes were ρN = 83.3 ± 2.0 fmol N cell–1 d–1 for NO3– and ρP = 5.5 ± 0.4 fmol P cell–1 d–1 for H2PO4– and did not exhibit significant differences between IB and IC modes. Under the prevailing experimental conditions, results show that IC mode involved very similar steady-state cell characteristics when compared to IB mode subsequent steady-state. IC mode could be an attractive alternative especially for experimental laboratory studies, as it should lead to higher flexibility in starting continuous cultures

How haptophytes microalgae mitigate vitamin B-12 limitation

Vitamin B-12 (cobalamin) can control phytoplankton development and community composition, with around half of microalgal species requiring this vitamin for growth. B-12 dependency is determined by the absence of cobalamin-independent methionine synthase and is unrelated across lineages. Despite their important role in carbon and sulphur biogeochemistry, little is known about haptophytes utilization of vitamin B-12 and their ability to cope with its limitation. Here we report the first evaluation of B-12 auxotrophy among this lineage based on molecular data of 19 species from 9 families. We assume that all species encode only a B-12-dependent methionine synthase, suggesting ubiquitous B-12 auxotrophy in this phylum. We further address the effect of different B-12 limitations on the molecular physiology of the model haptophyte Tisochrysis lutea. By coupling growth assays in batch and chemostat to cobalamin quantification and expression analyses, we propose that haptophytes use three strategies to cope with B-12 limitation. Haptophytes may assimilate dissolved methionine, finely regulate genes involved in methionine cycle and B-12 transport and/or limit B-12 transport to the mitochondrion. Taken together, these results provide better understanding of B-12 metabolism in haptophytes and represent valuable data for deciphering how B-12-producing bacteria shape the structure and dynamics of this important phytoplankton community

How haptophytes microalgae mitigate vitamin B-12 limitation

Vitamin B-12 (cobalamin) can control phytoplankton development and community composition, with around half of microalgal species requiring this vitamin for growth. B-12 dependency is determined by the absence of cobalamin-independent methionine synthase and is unrelated across lineages. Despite their important role in carbon and sulphur biogeochemistry, little is known about haptophytes utilization of vitamin B-12 and their ability to cope with its limitation. Here we report the first evaluation of B-12 auxotrophy among this lineage based on molecular data of 19 species from 9 families. We assume that all species encode only a B-12-dependent methionine synthase, suggesting ubiquitous B-12 auxotrophy in this phylum. We further address the effect of different B-12 limitations on the molecular physiology of the model haptophyte Tisochrysis lutea. By coupling growth assays in batch and chemostat to cobalamin quantification and expression analyses, we propose that haptophytes use three strategies to cope with B-12 limitation. Haptophytes may assimilate dissolved methionine, finely regulate genes involved in methionine cycle and B-12 transport and/or limit B-12 transport to the mitochondrion. Taken together, these results provide better understanding of B-12 metabolism in haptophytes and represent valuable data for deciphering how B-12-producing bacteria shape the structure and dynamics of this important phytoplankton community

Sharing Vitamin B12 between Bacteria and Microalgae Does Not Systematically Occur: Case Study of the Haptophyte Tisochrysis lutea

Haptophyte microalgae are key contributors to microbial communities in many environments. It has been proposed recently that members of this group would be virtually all dependent on vitamin B12 (cobalamin), an enzymatic cofactor produced only by some bacteria and archaea. Here, we examined the processes of vitamin B12 acquisition by haptophytes. We tested whether co-cultivating the model species Tisochrysis lutea with B12-producing bacteria in vitamin-deprived conditions would allow the microalga to overcome B12 deprivation. While T. lutea can grow by scavenging vitamin B12 from bacterial extracts, co-culture experiments showed that the algae did not receive B12 from its associated bacteria, despite bacteria/algae ratios supposedly being sufficient to allow enough vitamin production. Since other studies reported mutualistic algae–bacteria interactions for cobalamin, these results question the specificity of such associations. Finally, cultivating T. lutea with a complex bacterial consortium in the absence of the vitamin partially rescued its growth, highlighting the importance of microbial interactions and diversity. This work suggests that direct sharing of vitamin B12 is specific to each species pair and that algae in complex natural communities can acquire it indirectly by other mechanisms (e.g., after bacterial lysis)

Culture en continu de Isochrysis galbana affinis Tahiti

La prymnésiophycée Isochrysis galbana affinis Tahiti (T -iso) est une micro algue marine classiquement utilisée comme nourriture de larves de mollusques et de proies vivantes de poissons d'aquaculture dans la plupart des écloseries produisant des juvéniles de ces espèces. Aujourd'hui, de nombreuses écloseries de mollusques et de poissons l'utilisent en association avec d'autres espèces telles que Pavlova lutheri, Chaetoceros calcitrans et Skeletonema costatum. Isolée à Tahiti par JL Martin en 1975 (comm. pers.), cette algue s'est rapidement imposée dans la nutrition larvaire des crevettes et des mollusques en raison de sa croissance rapide en conditions tropicales et de ses qualités nutritionnelles, en relation avec sa forte teneur en acides gras polyinsaturés à longue chaîne

Procede de fixation de co2 et de traitement de dechets organiques par couplage d'un systeme de digestion anaerobie et d'un systeme de production de microorganismes phytoplanctoniques

L'invention concerne un procédé de fixation de CO2 et de traitement de déchets organiques, dans lequel on traite des microorganismes (105) issus d'une culture phytoplanctonique et des déchets organiques (104) dans un réacteur d'hydrolyse (101); on traite au moins une partie d'un effluent liquide (109) sortant du réacteur d'hydrolyse dans un réacteur de méthanisation (102); on traite une phase liquide (127) et du biogaz à épurer (110) sortant de l'étape (a") dans une unité de culture de microorganismes phytoplanctoniques (103); on injecte un effluent gazeux (113) contenant du CO2 dans l'unité de culture de microorganismes phytoplanctoniques; on maintient une concentration en NH3 inférieure à 0,5 g/L dans le réacteur de méthanisation; et on récupère un biogaz enrichi en méthane au sortir de l'unité de culture de microorganismes phytoplanctoniques. L'invention concerne également un système pour mettre en œuvre ce procédé