Oil accumulation by the oleaginous diatom Fistulifera solaris as revealed by the genome and transcriptome.

Oleaginous photosynthetic organisms such as microalgae are promising sources for biofuel production through the generation of carbon-neutral sustainable energy. However, the metabolic mechanisms driving high-rate lipid production in these oleaginous organisms remain unclear, thus impeding efforts to improve productivity through genetic modifications. We analyzed the genome and transcriptome of the oleaginous diatom Fistulifera solaris JPCC DA0580. Next-generation sequencing technology provided evidence of an allodiploid genome structure, suggesting unorthodox molecular evolutionary and genetic regulatory systems for reinforcing metabolic efficiencies. Although major metabolic pathways were shared with nonoleaginous diatoms, transcriptome analysis revealed unique expression patterns, such as concomitant upregulation of fatty acid/triacylglycerol biosynthesis and fatty acid degradation (ß-oxidation) in concert with ATP production. This peculiar pattern of gene expression may account for the simultaneous growth and oil accumulation phenotype and may inspire novel biofuel production technology based on this oleaginous microalga.

Membrane glycerolipid remodeling triggered by nitrogen and phosphorus starvation in Phaeodactylum tricornutum.

Diatoms constitute a major phylum of phytoplankton biodiversity in ocean water and freshwater ecosystems. They are known to respond to some chemical variations of the environment by the accumulation of triacylglycerol, but the relative changes occurring in membrane glycerolipids have not yet been studied. Our goal was first to define a reference for the glycerolipidome of the marine model diatom Phaeodactylum tricornutum, a necessary prerequisite to characterize and dissect the lipid metabolic routes that are orchestrated and regulated to build up each subcellular membrane compartment. By combining multiple analytical techniques, we determined the glycerolipid profile of P. tricornutum grown with various levels of nitrogen or phosphorus supplies. In different P. tricornutum accessions collected worldwide, a deprivation of either nutrient triggered an accumulation of triacylglycerol, but with different time scales and magnitudes. We investigated in depth the effect of nutrient starvation on the Pt1 strain (Culture Collection of Algae and Protozoa no. 1055/3). Nitrogen deprivation was the more severe stress, triggering thylakoid senescence and growth arrest. By contrast, phosphorus deprivation induced a stepwise adaptive response. The time scale of the glycerolipidome changes and the comparison with large-scale transcriptome studies were consistent with an exhaustion of unknown primary phosphorus-storage molecules (possibly polyphosphate) and a transcriptional control of some genes coding for specific lipid synthesis enzymes. We propose that phospholipids are secondary phosphorus-storage molecules broken down upon phosphorus deprivation, while nonphosphorus lipids are synthesized consistently with a phosphatidylglycerol-to-sulfolipid and a phosphatidycholine-to-betaine lipid replacement followed by a late accumulation of triacylglycerol.

Evolution of galactoglycerolipid biosynthetic pathways--from cyanobacteria to primary plastids and from primary to secondary plastids.

Photosynthetic membranes have a unique lipid composition that has been remarkably well conserved from cyanobacteria to chloroplasts. These membranes are characterized by a very high content in galactoglycerolipids, i.e., mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively). Galactoglycerolipids make up the bulk of the lipid matrix in which photosynthetic complexes are embedded. They are also known to fulfill specific functions, such as stabilizing photosystems, being a source of polyunsaturated fatty acids for various purposes and, in some eukaryotes, being exported to other subcellular compartments. The conservation of MGDG and DGDG suggests that selection pressures might have conserved the enzymes involved in their biosynthesis, but this does not appear to be the case. Important evolutionary transitions comprise primary endosymbiosis (from a symbiotic cyanobacterium to a primary chloroplast) and secondary endosymbiosis (from a symbiotic unicellular algal eukaryote to a secondary plastid). In this review, we compare biosynthetic pathways based on available molecular and biochemical data, highlighting enzymatic reactions that have been conserved and others that have diverged or been lost, as well as the emergence of parallel and alternative biosynthetic systems originating from other metabolic pathways. Questions for future research are highlighted.

Bioprospecting marine plankton.

The ocean dominates the surface of our planet and plays a major role in regulating the biosphere. For example, the microscopic photosynthetic organisms living within provide 50% of the oxygen we breathe, and much of our food and mineral resources are extracted from the ocean. In a time of ecological crisis and major changes in our society, it is essential to turn our attention towards the sea to find additional solutions for a sustainable future. Remarkably, while we are overexploiting many marine resources, particularly the fisheries, the planktonic compartment composed of zooplankton, phytoplankton, bacteria and viruses, represents 95% of marine biomass and yet the extent of its diversity remains largely unknown and underexploited. Consequently, the potential of plankton as a bioresource for humanity is largely untapped. Due to their diverse evolutionary backgrounds, planktonic organisms offer immense opportunities: new resources for medicine, cosmetics and food, renewable energy, and long-term solutions to mitigate climate change. Research programs aiming to exploit culture collections of marine micro-organisms as well as to prospect the huge resources of marine planktonic biodiversity in the oceans are now underway, and several bioactive extracts and purified compounds have already been identified. This review will survey and assess the current state-of-the-art and will propose methodologies to better exploit the potential of marine plankton for drug discovery and for dermocosmetics.

Mutations in CYC1, encoding cytochrome c1 subunit of respiratory chain complex III, cause insulin-responsive hyperglycemia.

Many individuals with abnormalities of mitochondrial respiratory chain complex III remain genetically undefined. Here, we report mutations (c.288G>T [p.Trp96Cys] and c.643C>T [p.Leu215Phe]) in CYC1, encoding the cytochrome c1 subunit of complex III, in two unrelated children presenting with recurrent episodes of ketoacidosis and insulin-responsive hyperglycemia. Cytochrome c1, the heme-containing component of complex III, mediates the transfer of electrons from the Rieske iron-sulfur protein to cytochrome c. Cytochrome c1 is present at reduced levels in the skeletal muscle and skin fibroblasts of affected individuals. Moreover, studies on yeast mutants and affected individuals' fibroblasts have shown that exogenous expression of wild-type CYC1 rescues complex III activity, demonstrating the deleterious effect of each mutation on cytochrome c1 stability and complex III activity.